03/06/2015

Author: Grzegorz Łabuz, Rotterdam Ophthalmic Institute, University of Murcia

According to global statistics, about 10 million people annually undergo cataract extraction with implantation of an intraocular lens (IOL). The blue light filtering IOLs are thought to be an important protector of the visual system against a blue-violet light. However, there has been some controversy regarding the extent of benefits which these IOLs might provide.

The blue-violet light is defined as a range between 380 nm to 500 nm of spectrum of light and is called a blue light. It is thought that exposing the eye to the blue light is harmful for the ocular tissue and debilitates the eye’s condition. It has been shown that the high intensity of the blue light yields to thermal damage of the retinal cells, and as a consequence, its necrosis. Although, exposure to s small dozen blue light might also result in chronic toxicity and trigger an oxidant stress. Because the retinal photoreceptors and the retinal pigment epithelial cells (RPE) are the most vulnerable to the oxidant stress, the long exposure of the retina on the blue light might increases the risk of occurrence AMD or pigmentary retinophatis. The vulnerability of RPE to the light phototoxity is caused by the accumulation of lipofucins. The light absorption peak of lipofuscin is at 440 nm, which stays behind the phototoxity of the blue light for the RPE.

On the other hand, the blue light exposure also has a good influence on our live. The discovery of the 3rd retinal photoreceptor has shown that the blue light is responsible for the circadian rhythm. The disturbance of the circadian psychological function might leads to insomnia as well as mood disorders. The blue light also guarantees a better scotopic perception by stimulation of the rods in low light conditions.

Therefore, the potential benefits and side effects should be carefully reviewed when considering implantation of the blue light filtering IOLs.

 01/06/2015

Author: Danilo Andrade de Jesus, Wrocław University of Technology

Ageing of the population has several consequences for the human visual system. The corneal tissue which is responsible for two thirds of the total optical power is not an exception, suffering structural and anatomical changes with the age. Recently, Danilo A. Jesus and D. Robert Iskander have explored the usefulness of Optical Coherence Tomography (OCT) speckle to study the age-related changes in corneal stroma. This study showed that Generalized Gamma distribution has a potential to fit the corneal speckle and could be a helpful complement to evaluate the structure and elastic properties of the cornea in vivo. The results of this study will be presented at 37^th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, in Milan, Italy, 25-29^th of August, 2015.

19/05/2015

Author: Cari Pérez Vives, PhD, Alcon Management (Switzerland)

Presbyopia may be corrected with monovision or multifocal contact lenses. Multifocal lenses are based on simultaneous vision, with the overlap of distance, intermediate and near images on the retina and have been reported to provide superior binocular vision and range of clear vision at near acuity relative to monovision, and to preserve stereopsis. In order to understand better these differences we performed a study with 24 presbyopic patients where we compared the visual performance of multifocal and monovision lenses using the objective measurements of stereoacuity, contrast sensitivity, defocus curves and the individual’s subjective ratings of vision with multifocal and monovision lenses. Multifocal lenses showed better defocus curves at intermediate and near ranges, better stereoacuity and contrast sensitivity and higher rates for all subjective parameters evaluated than monovision lenses. This study has been accepted as oral communication at annual clinical conference of the British Contact Lens Association that will take place in Liverpool, United Kingdom, 29-31 May 2015.

 19/05/2015

Author: Alejandra Consejo, Wrocław University of Technology

ARVO is the largest eye and vision research organization in the world. Its members include nearly 12,000 researchers from over 75 countries. ARVO conference is organized every year in a different city of United States. This year I could attend for the first time this important meeting which took place in Denver, Colorado. Thousands of posters, hundreds of talks… just in few days, from 3^rd to 7^th of May. Tiring but worthy. There I could present the latest results of my work by a poster presentation ´Determining the position of limbus corneae from anterior eye surface topography´ and having the feedback of many people working in the same field all over the world. New approaches to the problems to solve and new ideas to develop.  

See you in ARVO 2016… Seattle! 

5/05/2015

Author: Moulakaki A., I. BSc, MSc, University of Valencia

In the last decades, the majority of the multinational technology companies have filled the global market with consumer electronics. In the developmental history of such companies has been recorded the design of electronic devices, that changed for the better our everyday life. Hence, most of these devices -such as personal computers, electronic readers, smartphones and tablets- have nowadays become an integral and irreplaceable part of our daily life.

Day after day these electronic devices tend to be increasingly used by more people worldwide. Although they have contributed to make simpler our everyday routine, it has been also proved that they negatively affect our vision. Preliminary studies have reported eyesight symptoms, associated with ocular accommodation. Thus, recently in GIO labs a study has been conducted to examine if differences in accommodation response exist after subjects using different types of electronic devices. For the needs of this study a Hartmann-Shack wavefront sensor was employed, which was implemented into a prototype adaptive optics system. The results of this study yield an alternative approach of testing the accommodation response and the optical quality of the human eye in real time conditions, related with the change in society’s lifestyle by technology.

Figure: Adaptive Optics system including a Hartmann-Shack wavefront aberrometer, that can be employed as an individual system

27/04/2015

Author: Eleni Papadatou, M.Sc., University of Valencia

In order to evaluate the optical quality of intraocular lenses (IOLs), Modulation Transfer Function (MTF) is nowadays an international approved scientific method.^1,2 MTF, expresses the variation of image contrast with spatial frequency for an object with 100% contrast.³ The MTF measurement at a particular spatial frequency is called the Through Focus MTF (TF MTF) and it gives information about the depth of focus (DoF) that is provided by an optical system (an IOL in this case).

The axial MTF is the measurement of MTF within a defocus range, for a range of spatial frequencies. Successively measured axial MTFs, create a surface (figure 1) that gives information both for MTF and TF MTF configuration at the same time. Taking advantage of this surface, a new metric was developed in order to determine quantitatively the optical quality of IOLs by calculating the volume under the surface. Setting defocus intervals makes possible to isolate and calculate the volume under any desirable vergence of an IOL, providing this way valuable information about defocus tolerance and optical quality.

Furthermore, this new metric and can be generalized and assess the optical quality of any optical system by means of axial MTF.

Figure 1. Representation of the axial MTF configuration of a bifocal IOL for the 120 c/mm spatial frequency for a 3 mm aperture.

1. International Organization for Standardization. Ophthalmic Implants-Intraocular Lenses-Part 2: Optical Properties and Test Methods. Geneva, Switzerland, ISO, 1999 (ISO 11979-2); technical corrigendum 1, 2014.
2. International Organization for Standardization. Ophthalmic Implants-Intraocular Lenses-Part 9: Optical Properties and Test Methods. Geneva, Switzerland, ISO, 2006 (ISO 11979-2).
3. Thibos, Larry N., Xin Hong, Arthur Bradley, and Raymond A. Applegate. Metrics of Optical Quality of the Eye. Fort Lauderdale, Florida: ARVO, 2003.

20/04/2015

Author: Sonia Gholami, The Rotterdam Ophthalmic Institute

Physicians in ancient Persia played an important role in the development of medicine in the medieval era. One of the most influential figures of this era was Avicenna. Few researchers have looked into the different medical issues in his best known work, the Canon of Medicine, particularly with regard to ophthalmology. In this analysis, Avicenna’s views on and contributions to the diagnosis and treatment of cataracts in his Canon were elucidated.

According to the Canon, cataract is an obstructive disease in which external moisture accumulates between the aqueous humor and the corneal membrane and prevents images from entering the eye. Avicenna classified cataracts on the basis of size, density and color. According to size, he identified two types of cataracts including complete and partial obstruction. According to the Canon, surgical intervention was necessary only for certain indications. Avicenna believed that opacity in the initial stages of cataract could be diminished by medicines and foods, and described several medicines for cataracts. He believed that surgery should be postponed until the liquid accumulation stopped, and the cataract reached its mature state. After surgery, according to Avicenna, the patient should avoid headache-inducing situations because headaches could lead to edema of the layers of the eye. He further emphasized that the patient’s psychological status played an important role in the success of surgery.

Figure: This illustration from the Resaleh fi-alein shows the normal anatomy of the eye according to Avicenna. A, Conjunctiva; B, Optic nerve; C, Aqueous in anterior chamber; D, Aqueous in posterior chamber E, Vitreous.

Source:

Avicenna and Cataracts: A New Analysis of Contributions to Diagnosis and Treatment from the Canon

Iran Red Crescent Med J 2012; 14(5):265-270 ©Iranian Red Crescent Medical Journal

20/04/2015

Author: Georgios Zoulinakis, University of Valencia

In continuation of previous research in our labs on spherical surface IOLs (9/2/2015), we thought to evaluate whether it is better to place asphericities and conic constants on the anterior or posterior surface of an IOL. These changes on a spherical surface decrease the total spherical aberration of the eye with the IOL and result in better optical quality on the retina.

We used an optical design program to design spherical intraocular lenses of different dioptric powers from -10 to 40 Diopters. The power distribution between the surfaces of the IOLs was 70% - 80% of the total power on the anterior surface. The intraocular lenses were placed in the Navarro eye model and they were optimized with 1^st order asphericities and conic constants either on the anterior or the posterior surface. The eye models with the intraocular lenses were optimized to have the minimum root mean square (RMS) of aberration errors.

Our results were image simulations on retinal field, total RMS error, Zernike coefficients for sphere, spherical and secondary spherical aberration and diameter for RMS and Airy disks. The minimum aberrations and total RMS were found for the IOLs with asphericities and conics placed on the anterior surface. In the 40 D lens for example the RMS was found between 33 and 53 nm by using the anterior surface and between 170 and 306 nm by using the posterior surface. The optimization for the posterior surface asphericities and conics can give better corrections on aberrations and RMS errors if we use also 2^nd order asphericities.

The conclusion of our research is that the anterior surface can correct the total RMS error with less changes in comparison to the posterior surface of the IOL.

Figure

Letter F diffraction images with the IOL. On the upper line of the image the asphericities and conic constants are placed on the anterior surface of the lens, while on the lower line they are on the posterior surface of the IOL.

12/04/2014

Author: Matt Jaskulski, University of Murcia

1. Introduction

It is well documented that while reducing the retinal image quality, the chromatic aberration (CA)[1], may also aid the eye in the accommodation response[2][3]. The deficiencies of accommodation (i.e. accommodative lag) have been recently explored in terms of interplay between spherical aberration and defocus[4]. We created a computational model of the eye and performed a series of polychromatic through-focus simulations of image quality to analyze the effects of chromatic aberration on accommodation and depth of field.

2. Methodology

We performed a set of wavefront aberration measurements during accommodation in a group of young subjects under natural viewing conditions using the irx3 aberrometer (Imagine Eyes, France). The stimulus vergence was changed automatically in steps of about 0.5D to cover the entire AA span. We mext proceeded to compute polychromatic retinal image simulations. We followed the well established methodologies[6] for calculating first the PSF's (point- spread functions) and finally retinal images from monochromatic aberrations. We applied the process to each of the three channels of the target image that corresponded to the RGB primary colours – 700nm (R), 546.1nm (G) and 435.8nm (B). The three channels were then recombined into a single, polychromatic image. For each stimulus vergence we performed through-focus simulations of image quality spanning the whole AA of each subject. Every time an image simulating the effects of given eye's wavefront aberrations was generated from the target and various image quality metrics (such as the Visual Strehl Ratio) were calculated.

Figure 1. Test target (left), the well- (middle) and poorly (right) accommodated retinal image simulations. The R,G and B point-spread functions are shown below.

3. Results and discussion

Independently of viewing distance, the eye usually accommodates the minimum amount, enough place the target within its depth of field in order to see it relatively clearly[10]. Therefore, when one focuses at a nearby object, the eye accommodates a little further away, what constitutes a lag of accommodation. Our simulations have shown that in polychromatic light (which means in normal viewing conditions) the objective image quality is lower than in monochromatic light, however the effects of chromatic aberration extend the depth of field, which lowers the required accommodative effort on the part of the eye.

References

[1] N. López-Gil, A. Bradley, The potential for and challenges of spherical and chromatic aberration correction with new IOL designs. Br. J. Ophthalmol. 2012; 0:1–2.
[2] F.W. Campbell, The Depth of Field of the Human Eye, Optica Acta: International journal of Optics. 1957; 4:157-164.
[3] W.R. Bobier, M.C.W. Campbell, M. Hinch, The influence of chromatic aberration on the static accommodative response. Vision Res. 1992; 32:823-32.
[4] P. Bernal-Molina, R. Montés-Micó, R. Legras, N. López-Gil, Depth-of-field of the accommodating eye. Optometry and Vision Science. 2014; In-press.
[5] D. R. Iskander, M. J. Collins, B. Davis, L. G. Carney, Monochromatic aberrations and characteristics of retinal image quality. Clinical and experimental optometry. 2000; 1:83-6.
[6] B. Wang, K. J. Ciuffreda, Depth-of-Focus of the Human Eye: theory and Clinical Implications. Survey of Ophthalmology. 2006; 1:76-85.

1/4/2015

Author: Juan F. Zapata-Díaz, University of Manchester

Depth-of-focus is a characteristic of any optical system that allows sharp images to be formed at certain distances out of focus of the system. The human eye also counts on with this characteristic.

In last years, great interest has been taken into this property of the human eye due to the aid that it could represent to improve approaches to correct presbyopia. Contact lenses or intraocular lenses with an extended depth-of-focus may be able to simulate partially the accommodation mechanism of the eye (which is progressively lost with the development of presbyopia). This is the reason why researches have been trying to achieve these new approaches.

But human vision does not only depend on the optical part of the eye, since neural factors are also involved in vision and depth-of-focus of the human eye. This creates the need to separate both, optical and neural factors in order to study depth-of-focus objectively.

One of the partners of the Ageye Consortium, the Biomedical and Signal Processing Group (Wroclaw University of Technology, Poland), directed by Dr. Robert Iskander, has wide experience in developing methods to study depth-of-focus objectively through image quality metrics. One of these methods comprises the use of objective measurements of the imperfections of the eye (optical aberrations) and pupil size to calculate image quality at focus and at certain distances out of focus (through-focus analysis). With this technique, estimation of objective depth-of-focus can be achieved following objective criteria and avoiding the influence of neural factors.

Figure 1. Example of through-focus analysis of image quality.

 25/3/2015

Author: Irene Sisó Fuertes, University of Manchester

Nowadays diverse solutions to correct presbyopia are available in the market. Their main goal is to provide spectacle-free vision correction for the presbyopic population. One of the most accepted alternatives to correct presbyopia are contact lenses based on simultaneous vision – this is to say that both distance and near correction zones are allocated within the pupillary area providing simultaneous correction for both distances - but they only represent the 15% of the annual total fits. Therefore, studying their optical performance and interaction with accommodation provides better understanding and cues to improve current solutions for presbyopia correction and the number of people willing to adapt to them. Thus, we conducted a study to investigate the improvements achieved, if any, by the PureVision2 High add (Bausch & Lomb) bi-aspheric multifocal contact lens with respect to its predecessor PureVision High add. We did so in terms of visual acuity, accommodative response and ocular aberrations. This study has been accepted for poster presentation at the seventh annual conference of the European Academy of Optics and Optometry that will be held in Budapest, Hungary, 14-17 May 2015.

20/3/2015

Author: Grzegorz Łabuz, Rotterdam Ophthalmic Institute, University of Murcia

According to the World Population Ageing 1950-2050 report [1], issued by the United Nations, population ageing is a global phenomena affecting every country. The proportion of people aged 60+ is steadily increasing, and without any changes, their number will exceed the number of young persons. In the more developed countries, the percentage of ageing adults in the society might raise from 20% in 2000 to 33% by 2050. This demographic shift would have an important effect not only on the socio-economical processes, but also cause structural and functional consequences for the human visual system.        

The study by IPSOS (2011) [2] showed that the major visual problems, reported  by 60% of patients aged 60 years and more, are related to light conditions. Difficulties with reading under a dim light, elevated sensitivity to bright light sources and decreased vision at night are the most common visual symptoms mentioned by respondents. The other difficulties stressed by elderly patients were: reading small print (e.g. medical instructions), lower contrast while looking at colored backgrounds and irritability to sunlight. Around 17% of those who responded also indicated disability glare as real hindrance in their daily life. It might be related to increase of intraocular straylight with age, as a result of the natural senile process of the eye. However, those symptoms might become more common, affecting around 75% of patients, and severe once cataract develop. To restore normal vision a cataract surgery is performed, but it has been shown, that in some cases surgery only alleviates the mentioned symptoms. It was presented in the study by Labuz et al. [3] that glare and excessive light sensitivity might bother patients after the crystalline lens replacement (Figure 1). Although, the reason of the straylight elevation in some patients after cataract surgery is still not clear. Therefore, the aim of the project “Intraocular scattering through different optical designs” is to determine sources of increased prevalence of glare and other visual disabilities in patients after cataract surgery. 

Figure 1. Intraocular straylight as a function of age. The red rectangle indicates elevated level of straylight (disability glare) in normal pseudophakic eyes [3].  

References

1. The United Nations. Department of Economic and Social Affairs Population Division. World Population Ageing 1950-2050. New York, the USA, 2001.
2. IPSOS  Public Affairs, Observatoire de la Maturité, 2011.
3. G. Łabuz, N.J. Reus, T.J.T.P van den Berg. Ocular straylight in the normal pseudophakic eye. J Cataract Refract Surg (in press). 

10/3/2015

Last weekend, 7 and 8 of March 2015, the Annual Meeting of Ageing Eye (Marie Skłodowska-Curie ITN Action) took place in Valencia.

More than 16 scientists and professors participated and presented topics around vision, optics, optometry and fields associated with the eye and the effects of time on the accommodative system. Between them, the Early Stage Researchers, fellows of the Ageye program presented their own topics in their fields of expertise.

The meeting had large attendance from many scientists and students. We thank you all for that and we hope to see you in the next Ageing Eye Annual meeting.

(Special thanks to Matt Jaskulski for the photos)

10/3/2015

Author: Alejandra Consejo, Wrocław University of Technology

Nowadays scleral contact lenses (SCL) are becoming more and more popular. Ocular surface diseases and cornea irregularity such as keratoconus are the major indications for this kind of contact lenses. Last January I had the chance of attending the GSLS (Global Speciality Lens Symposium) in Las Vegas, USA. There not only the state of the art of SCL was presented by the Scleral Lens Education Society but also the last research in the field was shown by different well-known scientists. If something differentiate this meeting from other I’ve been it is its practical point of view. The whole symposium was crowded with practitioners, people who are used to deal with patients everyday rather than working in a lab. That makes you get the feeling of which are the real challenges and the real necessities that must be solved, what the market is demanding and what should be the future challenges to commit. Being part of this audience was encouraging, it made me realize that the results from my current research, this is presenting an accurate model which describes the anterior part of the eye, might be really useful for solving a real and actual problem, not just an academic exercise.

Probably one of the major advantages of being part of this AGEYE huge European project is precisely having the opportunity of exchanging information. Last week OC’15 Ageing Eye Annual meeting was celebrated in Valencia, Spain, which was an opportunity to present to the community the research that has been developed till now, somehow was itself an exchange of knowledge, not only between fellows but also with professionals from the field of vision, from business and academic world. That mixture, that difference in points of views, in how to approach a problem opens your field of vision, because in the end that’s what all this is about, learning, grabbing new ideas, comparing results, sharing knowledge… making science.

Oral presentation during the OC´15 Ageing Eye Annual meeting in Valencia, Spain. (Picture courtesy of Matt Jaskulski)

10/3/2015

Author: Danilo Andrade de Jesus, Wrocław University of Technology

The limbus is defined as a border or a transition zone between the optical clear cornea and the opaque sclera [1,2]. Furthermore, it is a niche for stem cell population that can give rise to differentiated endothelial cells [3]. These cells are important for maintaining the clear state of the cornea since its deficiency results in the inability to replace the corneal epithelium resulting in chronic inflammation, vascularization, and even blindness. Once the limbus has been predicted other parameters such as the corneal centroid, which is important for corneal transplantation [4], contact lens fitting [5] or tracking the eye movements during refractive surgery [6], can be easily achieved.

Anatomically, the limbus epithelium gradually thickens toward the sclera and its radius of curvature could change abruptly at the junction of cornea and sclera creating a shallow furrow. In order to more accurately identify the position of the corneoscleral transition than the traditional imaging techniques (so called Horizontal Visible Iris Diameter or the White-to-white corneal diameter), the Eye Surface Profiler, a newly developed instrument based on the principle of profilometry, was used. Its 3D topographical data allowed to develop two new methods for limbus demarcation.

The first method used Zernike polynomials to separately model the inner (corneal) and outer (scleral) regions of the anterior eye in a circular domain. Bhatia-Wolf polynomials were used in the second method where the 3D data was enhanced using the 2D grayscale image of the eye. The corneoscleral fitting of both methods allowed to demark the corneoscleral transition zone according to its curvature as shown on figure (1). The method based on Bhatia-Wolf polynomials showed to be more precise and robust than the method based on Zernike polynomials when the corneoscleral data is not fully accessible. Our results suggest that these methodologies can be helpful to be adopted in ophthalmic applications where high precision in outlining the limbus characteristics is required.

Figure 1 – Eye Surface Profiler image with the limbus position estimated by the method based on Zernike polynomials (a) where the grey square is enlarged in (b). The yellow and white lines are the extremes of the corneoscleral transition and the red line the central position of the limbus. The image (c) outlines the corneoscleral transition through the method based on Bhatia-Wolf polynomials. The central position of the limbus (red line) obtained in (c) and its circular fitting (blue line) are shown in (d).

References
[1] E. M. Van Buskirk, “The anatomy of the limbus.,” Eye (Lond). , vol. 3 ( Pt 2), pp. 101–8, Jan. 1989.
[2] P. Ordonez and N. Di Girolamo, “Limbal epithelial stem cells: role of the niche microenvironment.,” Stem Cells, vol. 30, no. 2, pp.100–7, Feb. 2012.
[3] S. L. McGowan, H. F. Edelhauser, R. R. Pfister, and D. R. Whikehart, “Stem cell markers in the human posterior limbus and corneal endothelium of unwounded and wounded corneas.,” Mol. Vis., vol. 13, no. May, pp. 1984–2000, Jan. 2007.
[4] A. Langenbucher, B. Seitz, M. M. Kus, E. Vilchis, and G. O. Naumann, “Graft decentration in penetrating keratoplasty: nonmechanical trephination with the excimer laser (193 nm) versus the motor trephine.,” Ophthalmic Surg. Lasers, vol. 29, no. 2, pp. 106–13, Feb. 1998.
[5] R. B. Mandell, C. S. Chiang, and S. A. Klein, “Location of the major corneal reference points.,” Optom. Vis. Sci. , vol. 72, no. 11, pp. 776–84, Nov. 1995.
[6] J. Schwiegerling and R. W. Snyder, “Eye movement during laser in situ keratomileusis.,” J. Cataract Refract. Surg., vol. 26, no. 3, pp. 345–51, Mar. 2000.

23/2/2015

Author: Moulakaki A., I. BSc, MSc, University of Valencia

Nowadays, it is well established that the amplitude of accommodation decreases with age. However, the age related changes in the dynamics of accommodation are not well characterized. Hence, studies on the accommodative dynamics provide insight into the accommodation mechanism and the factors that influence on the accommodative responses. This results to gain knowledge of the age related changes in the accommodative dynamics induced with conditions, such as presbyopia. Furthermore, although there are potentially many effective methods for treating presbyopia (e.g. spectacles, multifocal contact lenses, monovision, etc), it is of great interest to manage the true restoration of active and dynamic accommodation, as it would provide a dynamic change in optical power of the eye with an effort to  focus at near.

A preliminary study aimed to investigate if age-related changes have an effect on the ocular dynamic accommodative characteristics and to identify the impact of accommodative IntraOcular Lens on the aging accommodative system. To achieve this, continuous dynamic responses recorded with a moving target, while subject’s aberrations have been removed and replaced with those of pseudophakes viewing with the lens. In particular, the intraocular structures that dominate dynamic accommodative system changed with aging and the progression of presbyopia. Moreover, the dynamic accommodating effects of the lens appeared to be limited, however subjects viewing with this lens were able to track a moving target and achieve an adequate visual acuity. Pseudophakic accommodative responses were similar in dynamics with the presbyopic accommodative responses.

Figure 1: Dynamic accommodation measurements (in D) for different stimulus magnitudes

(Source: Kasthurirangan, S. (2014). Current Methods for Objectively Measuring Accommodation. In: Developing Novel Endpoints for Premium Intraocular Lenses. American Academy of Opthahlmology.)

Figure 2: Objective amplitude of accommodation (dashed line) and dynamics of the lens (solid line) of one subject 

16/2/2015

Author: Eleni Papadatou, University of Valencia

Implantation of multifocal intraocular lenses (MIOLs) has been proved a successful method of refractive surgery in order to restore satisfactory the quality of vision after cataract removal. Toric MIOLs aim to provide good near vision with distance correction and correct also the astigmatism. Innovations in both lenses construction and surgery techniques have optimized the surgical procedure (e.g. smaller incisions). Nevertheless, phenomena related with the stabilization of the lens postoperatively occur and may affect the visual outcome. In the labs of GIO we examine in vitro the optical quality of bifocal and trifocal diffractive toric MIOLs in simulated conditions of decentration, tilt and rotation under photopic and mesopic conditions. The evaluation is performed by means of Modulation Transfer Function (MTF) that is an internationally approved method for testing the optical quality of an optical element (ISO 11979-2, ISO 11979-9).

Image: diffractive bifocal toric MIOL.

The results so far demonstrate that decentration and tilt have a gradual impact on the optical quality of the lenses that can be interpreted as deterioration of the visual performance. Moreover, the power of the IOL has an inverse relationship with decentration tolerance limit. That means the higher the power of the lens is the lower the amount of decentration that does not decay the optical quality of the lens. Tilt, seems to have a greater impact in optical quality than decentration. It is important to take into account that these phenomena happen at the same time when the lens is implanted. In future, the next step is to examine the effect of rotation, which we expect to have the greatest impact on toric MIOLs optical quality.

Figure: Through focus MTF curves of bifocal toric MIOL, at centered, decentered and tilted positions for a 3mm aperture.

9/2/2015

Author: Georgios Zoulinakis, University of Valencia

The power of an intraocular lens (IOL) is defined by its refractive index, the refractive index of the aqueous, the thickness and the power of the two surfaces of the lens. The refractive index of an IOL is fixed between 1,45 and 1,55. The refractive index of the aqueous is also fixed at 1,37. The question is about the effect of the geometric parameters of the lens on the optical quality that it provides. If we suppose that the thickness of the lens is also fixed, around 1 mm, only the two surfaces remain to be changed. A new project has started in the University of Valencia, about the optical quality and the visual performance of many IOLs with the same total power, changing only the anterior and posterior surfaces’ powers. In this project we have taken categories of lenses with power between -10 and 40 Diopters. In all lenses we have chosen a standard thickness, refractive index and position behind the pupil. The powers of the anterior and posterior surfaces are changed by changing the radius of curvature of both surfaces in respect, so that the total power remains the same.

Our results up to now concern only spherical surface lenses. It seems that as the power of the anterior surface is growing up to between 70% - 90% of the total power of the IOL, the total RMS error (Root Mean Square) and spherical aberration of the whole system of the eye model including the IOL is getting smaller.

 Top: image on retinal plane of the model Bottom: image on retinal plane of the model.

 2/2/2015

Author: Sonia Gholami, The Rotterdam Ophthalmic Institute

The image-forming properties of the eye can be fully described by the wave aberrations. The wavefront error of the eye can be described by normalized Zernike polynomial (ZP) expansion. This expansion is widely used in optics because ZPs form a complete orthogonal basis on a circle (e.g., pupil) of unit radius and with few coefficients, it traces an entire wavefront aberration (WFA) map. In one study (Marsack et al., 2004), it has been shown that the visual Strehl ratio (VSR) metric accounts for 81% of the variance in high-contrast logMAR visual acuity (VA) which makes this metric a strong predictor of visual performance in normal eyes. We apply this method and investigate the correlation between the VA and the VSR of the eyes with cataract. The VSR metric is calculated using the modulation transfer function method (VSMTF). The WFA of the eye will be measured by SCHWIND SIRIUS (Scheimpflug Analyzer). We measure the ocular and corneal monochromatic WFAs and obtain information on the intraocular WFA by subtracting the corresponding ZP coefficients.

 Figure. This chart reveals lower order aberrations (LOA) created when a WF of light passes through eyes with imperfect vision. A theoretically perfect eye (top) is represented by an aberration-free plane known, for reference, as piston. (Image: Alcon Inc.)

27/1/2015

Author: Matt Jaskulski, University of Murcia

Recently it has been proven that spherical aberration has influence over the depth of field (DOFi - our span of sharp vision when looking at a certain distance) and the accommodation lag (Bernal-Molina et al., OVS, 2014). We are currently researching if the longitudinal chromatic aberration (LCA) also plays a role in increasing the DOFi during accommodation, thus effectively extending its range.

We built a custom-designed adaptive optics system that can measure, save, compensate and induce in real time all of the aberrations (imperfections) of a subject's eye. Its three essential components are:

• An infrared diode - whose beam of light is directed into the eye. The light that is reflected from the retina and exits the eye through the pupil. It is then being measured by a Hartmann-Shack sensor.
• The Hartman-Shack type sensor - comprising of an infrared-sensitive camera and an array of over 1000 micro-lenses in front of it. It is used to precisely map the wavefront of infrared light originating from the eye. It is then saved as a Zernike-polynomial expansion.
• A deformable mirror – that is able to deform itself and assume any curved shape by means of 52 piezo-electric actuators beneath it's surface. Working in a closed data loop with the Hartmann-Shack sensor it can adapt itself to the aberrations of the eye contained in the measured wavefront and compensate them completely giving the subject perfect vision. It is also possible to give any subject the vision as seen through optics of an eye of another person or induce any previously stored wavefront aberration maps.

We use this system to research the effects of the longitudinal chromatic aberration (a phenomenon that arises from the fact that the spectrum of light our eyes are sensitive to doesn't focus exactly on the retina – the blue, short-wavelength light focuses in front, and the red, long-wavelength light behind it) on the DOFi and the lag of accommodation (another phenomenon that arises from the fact that our eyes accommodate, or bring objects into focus only the minimum required amount, doing the least possible effort). We discovered that this span is twice as large when considering red, green and blue light separately than when considering white light that we perceive in everyday life. In other words the DOFi due to the chromatic aberration (the dioptric span between the outer limits of the R and B DOFi) was on average 1.9 times larger than the DOFi found for the white light.

Image: Optotipes on a microdisplay as seen by the subject through the adaptive optics system.

19/1/2015

Author: Juan F. Zapata-Díaz, University of Manchester

Empirical eye models have been widely used to further understand the optical mechanisms of the eye. Current non-paraxial eye models take into account surfaces asphericity and changes during accommodation and age and include a GRIN lens. However, none of them include the pupil-related changes during accommodation and age, which may be an important parameter in a non-paraxial eye model.

A new eye model based on “in vivo” measurements was presented at the last Visual and Physiological Optics conference (VPO2014) in Wroclaw (Poland). This model includes the effect of accommodation and age on all optical parameters, including pupil size. The model is able to simulate the eye wavefront and to predict changes in refraction, accommodation response, and spherical aberration with accommodation and age. This makes the model a good tool to design and test new approaches to correct visual dysfunctions and to study optical factors influencing some of the eye features such as depth-of-focus.

Figure 1. Three-dimensional representation of the proposed eye model for an unaccommodated state and for a 35-years-old case.

12/1/2015

Author: Irene Sisó Fuertes, University of Manchester

Accommodation is the capability of the human eye to change focus in order to maintain a clear image of an object as its distance varies. Despite the fact that nowadays the lens is established to be the ocular structure that suffers the principal anatomical changes during accommodation, the cornea is known to be a very malleable entity whose changes whilst accommodating still remain unsure. This is the reason why a study was conducted to assess whether corneal parameters and aberrations are affected by accommodation. A dual Scheimpflug photography device was used to obtain data on anterior and posterior axial curvature, total corneal power and corneal pachymetry from three different corneal zones including a more peripheral corneal area (7-10 mm) than in previous studies due to the usage of the latest technology of Galilei G4. Twelve young emmetropic eyes in unaccommodated and four accommodated states were evaluated. Second, third and four-order aberrations as well as the root mean square were also collected for the entire cornea at the same accommodative demands. Results showed no significant (p > 0.05) changes in any of the measured parameters during accommodation for any of the corneal zones. However, statistically significant differences (p<0.01) were found in the various corneal zones when assuming they are constant with accommodation. A stable lineal trend with accommodation was also found for corneal aberrations, although individual variations exist because of the high standard deviation values. All these results suggest that different parameters in various zones of the cornea as well as corneal aberrations are stable during accommodation and will be published in the Journal of Cataract & Refractive Surgery.

Figure 1: Function of Galilei G4. Thanks to its duality, Galilei captures slit images from opposite sides of the illuminated slit, and averages the elevation data obtained from corresponding opposite slit images. This reduces possible decentration errors caused by ocular movements.

Figure 2: Schematic drawing that demonstrates the changes occurring during accommodation.

9/1/2015

Author: Grzegorz Łabuz, Rotterdam Ophthalmic Institute, University of Murcia

The imporatance of straylight on the visual system has been studied since the beginning of the 20^th century.  Straylight is produced by small inhomogeneities in the eye’s optical media caused by changes in refractive index. Due to the senile process of the crystalline lens number of ihomogeneities increase with age, and it results in the gradual increase of straylight despite of good visual acuity. Aging of the eye also leads to the cataract disorder which appears as an opacification of the natural lens and straylight elevation. It leads to severe functional difficulties like disability glare (e.g. blinding by oncoming car’s headlights, Figure 1), hazy vision and the loss of contrast and color vision as well. The literature has shown that cataract surgery is effective in reducing straylight. However, some healthy patients, after uneventful cataract surgery, have either no change or an increase in straylight upon crystalline lens exchange. This may result in postoperative dissatisfaction, even though visual acuity is good. To avoid disappointment following cataract surgery it is important to know what straylight value can be expected in pseudophakic eyes. Therefore, the retrospective cross-study data analysis was performed to establish a new reference for straylight, obtained by the C-Quant (Oculus Optikgeräte GmbH, Wetzlar, Germany) in the normal pseudophakic eyes. The pseudophakic norm might be considered as a predictive feature to improve the decision-making process before cataract surgery as well as to minimize the potential for disability glare and patient dissatisfaction. The results of this study, including the new pseudophakic norm and the model of straylight improvement following cataract surgery have already been submitted and will be published in the Journal of Cataract & Refractive Surgery.

Figure 1. The visualisation of disability glare. The simulation was performed using the scattering filter (Encyclopedia of Eye, 2010, vol. 3, pp. 173-183).  

30/12/2014

Author: Alejandra Consejo, Wrocław University of Technology

Traditionally, the limbus has been assumed to coincide with the HVID or the white-to-white (W2W) radius estimated from 2D “en face” intensity images. Recently, a new technology based on the principle of profilometry, which has the potential of measuring the corneo-scleral topography extending the acquired area up to 20 mm diameter far beyond the limbus, has become available. Studying the 3D corneo-scleral topography is possible using this technology. Of interest was whether the 3D anterior eye scleral topography could be utilized to demarcate the limbal area based on local curvature. That topography-based limbus demarcation is not a trivial task. There are no standards. Moreover, the results depend on the limbus definition as well as the technique used for its estimation. With more advanced technologies becoming readily available, one is able to choose a specific definition of limbus (e.g., based on HVID, W2W, or topography based) suitable for his or her particular purposes. The proposed topography-based estimation of the limbus location can be particularly attractive for scleral contact lens design and fit. The first results of this study were presented in a conference poster on the Visual & Physiological Optics conference, August 2014 in Wrocław (Poland). Later on, the following steps of this work were presented at the 12^th Students’ Conference, September 2014 in Boguszów-Gorze (Poland), where I achieved the first conference prize in the category Bio-chem-sphere (Images) for this work made in collaboration with my supervisor Robert Iskander.

Image 1: Oral presentation in the 12^th Students’ Conference explaining the presented study “Modelling of the anterior eye topography focusing on identification of the limbal region”.

Image 2: Receiving the Bio-chem-sphere prize from Professor Zbigniew Sroka.

29/12/2014

Author: Danilo Andrade de Jesus, Wrocław University of Technology

Recently a method that simplifies calculation of geometrical point spread function has been proposed for circularly symmetric systems (Gagnon et al., App. Opt. 2014). The method is based on Chebyshev polynomials and it is realized with the help of Matlab Chebfun toolbox – a new tool for computing with functions developed at Oxford University. An extension of this method to 2D non-circularly symmetric systems was proposed by Danilo A. Jesus and D. Robert Iskander and currently submitted to ARVO 2015 Meeting in Denver, CO. In this method, surfaces, rays, and refractive indices are all represented in functional forms being approximated by Chebyshev polynomials. Although not all properties of 1D Chebyshev polynomials are present in their 2D representations, there are many benefits of using them including the ease of surface representation, manipulation of multiple surface designs, and the ability to represent gradient index (GRIN) type lenses.

Such a representation appears to be an ideal tool for performing ray tracing in anatomically correct eye models such as the one proposed by Liou and Brennan (Figure 1). It was established that computational complexity (assessed as the CPU time) increases with the addition of each surface in a linear form indicating that the method has a great computational potential to be used for more intricate eye models in which, for example, the crystalline lens is described with multiple surfaces. Performing ray tracing with Chebfun toolbox substantially simplifies calculations as it is based on object oriented programming with handle functions. Realization of the ray tracing technique in Matlab is particularly attractive among researchers for whom other ray tracing optical engineering packages such as those employed in Zemax are more cumbersome and sometimes difficult to acquire. 

 Figure 1: An example of chebfun-based ray tracing using the anatomically correct eye model of Liou and Brenner (JOSA A, 1997) where all the distances corresponds to millimeters.

15/12/2014

Author: Moulakaki A., I. BSc, MSc, University of Valencia

The amount of studies conducted for estimating the age related effects in both structural and functional components of the human visual system has been remarkably increased the last two decades. However, prior to investigating the age related loss of eye’s ability to focus at different distances, it is of major importance to understand how the young eye behaves, as there are other sources of variation that influence on the optical quality during accommodation. In a preliminary study conducted for the needs of the XXXII European Society of Cataract and Refractive Surgery (ESCRS) congress, we examined the relationship between visual acuity and accommodative response, as a function of age, for natural pupil size among young normal subjects. To achieve this, a maximum likelihood adaptive procedure was employed in a healthy population with unblurred and blurred Landolt Cs stimuli sets (Figure). Minor differences were found in the measured accommodative response for each of the conditions presented. An over-accommodation and an under-accommodation were detected for the further and closer targets, respectively. Visual acuity for the distant stimuli was significantly poorer than for the other conditions, due to increased accommodative lead associated with proximal accommodation. The accommodation response was deteriorated with the most blurred stimuli, as the accommodation system was made optimal use of its available amplitude and depth-of-focus of the eye.

Figure: Unblurred and blurred Landolt Cs images generated with artificial blur to the stimulus.

8/12/2014

Author: Eleni Papadatou, University of Valencia 

Several designs of soft multifocal contact lenses are currently available in the market to serve the aim of functional vision in a range of distances.  Soft materials are popular in the construction of contact lenses due to the comfort they provide and the high values of Dk they offer. Nevertheless, a problem that frequently arises is the stabilization of the lenses when they are fitted in the eye, which affects the centration, and hence it can affect the visual outcome, especially in the case of a multifocal contact lens. In the XXXII Congress of the European Society of Cataract and Refractive Surgery, September 2014 in London, an electronic poster was presented by Eleni Papadatou (Image) which assessed the in vitro changes on power profile of a simultaneous vision designed, refractive zoned multifocal contact lens for different degrees of decentering (from 0.0mm, aka centred position, up to 1.00 mm) and evaluate the effect in the optical outcome. The results demonstrated that the decentration led gradually to a shift on the power profile of the lens, which was lacking its symmetry as the decentration increased. That means that for a fixed pupil size the combination of powers was different at every step of decentration, which indicates that pupil size plays an important role when the lens is well centred. Thus, the optical outcome at decentred conditions seems to be more dependent on other, non-fixed factors such as the intraocular suppression ability, which varies between the individuals and finally, may enhance or deteriorate the visual outcome.

Image: Eleni Papadatou presenting her electronic poster in the XXXII ESCRS Congress 2014, London

1/12/2014

Author: Georgios Zoulinakis, University of Valencia

Optical modeling and engineering are two research fields that combine many sciences together such as ophthalmology, optometry, physics etc. These fields provide us with knowledge and model eyes that help us simulate different accommodative status. In the XXXII Congress of the European Society of Cataract and Refractive Surgery, September 2014 in London an electronic poster was submitted by Georgios Zoulinakis. In this poster is presented a comparison between three different human model eyes, in different accommodative status, which were designed with and optical design program. There is also a comparison between model eyes that simulate healthy and presbyopic situations. In the results were presented graphs of the MTFs, spot diagrams and diffraction images of a “letter F” in different distances. It was concluded that optical design programs help us to design model eyes that can simulate many different parameters. There is no perfect model until now that can simulate every optical parameter, but the use of each model is specified for different parameters. These models can be configured and used in further research for designing contact and intraocular lenses.

The studies are the first developed through the 2012 NIH Alzheimer’s Disease Research Summit, according to an NIH announcement.

“We know that Alzheimer’s-related brain changes take place years, even decades, before symptoms appear,” NIH Director Richard Hodes, MD, said in the announcement. “That really may be the optimal window for drugs that delay progression or prevent the disease altogether. The clinical trials getting under way with these funds will test treatments in symptom-free volunteers at risk for the disease, or those in the very earliest stages — where we hope we can make the biggest difference.”

The Sapphire II test by Cognoptix showed a sensitivity of 85% and specificity of 95% in differentiating 20 patients diagnosed with probable Alzheimer’s disease from a group of 20 age-matched controls, according to a company press release.