Changes in spherical aberration after lens refilling with a silicone oil

PURPOSE. It may be possible to restore accommodation to presbyopic human eyes by refilling the lens capsular bag with a soft polymer. In the present study, optical changes were measured that occurred in a pig eye model after the refilling of the capsular bag. METHODS. The optical power and spherical aberration in 10 isolated pig lenses were measured under different conditions. They were first determined by using a scanning laser raytracing technique over an effective pupil size of 6 mm. Second, the contours of the anterior and posterior lens surface were photographed, and a mathematical ray-tracing was performed by using a polynomial fit through the digitized surface contours, to determine optical power and spherical aberration. Third. the lenses were refilled with a silicone oil until their preoperative lens thickness was reached, and scanning laser ray-tracing, contour photography, and mathematical ray-tracing were repeated. Comparisons between the measurements were made to determine how the change from a gradient refractive index to a homogeneous refractive index influenced spherical aberration. The influence of the change in lens contour on spherical aberration after lens refilling was also studied. RESULTS. The natural lenses had a higher lens power than the refilled lenses (49.9 +/- 1.5 D vs. 36.8 +/- 1.5 D; P <0.001). Moreover, there was a change in sign from negative spherical aberration before lens refilling (-3.6 D) to positive spherical aberration after lens refilling (7.9 D; P <0.001). The comparison between scanning laser ray-tracing of the natural lens and mathematical ray-tracing of the photographed surface contours of the natural lens to determine the effect of refractive index substitution (i.e., replacement of a gradient refractive index by a homogeneous refractive index) showed a significant change in spherical aberration from -3.6 +/- 2.0 to 11.0 +/- 2.1 D (P <0.001). The change in lens contour did not result in a significant change in spherical aberration (P = 0.08) before and after lens refilling with an equal refractive index. CONCLUSIONS. The lower lens power of refilled pig lenses compared to natural lenses was due to the lower refractive index of the refill material. Refilling pig lenses with the silicone oil used in this study resulted in an increase in spherical aberration. This increase was mainly caused by the change from a gradient refractive index to a homogeneous refractive index. The change in lens curvature after lens refilling did not result in an increase in spherical aberration. The influence of lens refilling on spherical aberration of human lenses must be determined in similar experiments in human eyes

7.1 T MRI to Assess the Anterior Segment of the Eye

PURPOSE. Visualization of the anterior segment and biometric evaluation of the entire crystalline lens pose significant challenges for imaging techniques because of tissue-induced distortion artifacts. The present study was conducted to demonstrate the advantages of high-resolution magnetic resonance imaging (micro-MRI) for visualizing the anterior segment. METHODS. High-resolution MR ocular images were acquired on an ultra-high-field MR unit using a two-channel coil with four coil elements and T(2)-weighted turbo spin echo sequences ex vivo in pig, rabbit, monkey, and human donor eyes and in vivo in rabbits. Tissue heating, reproducibility, and signal-to-noise ratio were investigated in vivo. Monkey eye lens thickness (LT) was also measured using A-scan ultrasonography (US). RESULTS. Anterior segment details of phakic eyes were obtained ex vivo (pig, rabbit, monkey, and human donor eyes) with pixel matrix size 512 x 512 (in-plane resolution 80 x 80 mu m) and in vivo (rabbit eyes) with pixel matrix size 320 x 320 (in-plane resolution 125 x 125 mu m). Complete quantification of lens dimensions as they correlate with the sulcus-sulcus and angle-angle plane can be performed. In LT determinations in monkey eyes, no significant difference was detected between micro-MRI and A-scan US (P > 0.05, Mann-Whitney U test). Biometric analysis of one pseudophakic monkey eye confirmed the absence of relevant distortion artifacts. CONCLUSIONS. Micro-MRI allows ex vivo and in vivo visualization and quantification of the spatial arrangement of the anterior eye segment. Imaging of the retroiridian region, including the entire crystalline lens, overcomes a number of major limitations in the quantitative evaluation of the anterior segment. (Invest Ophthalmol Vis Sci. 2010; 51: 6575-6581) DOI:10.1167/iovs.09-486

Prevention of capsular opacification after accommodative lens refilling surgery in rabbits

Silicone gel-like polymers have been proposed to replace the cataractous lens and therewith restore both vision and accommodation. Lens replacement is associated with opacification of the capsular bag due to the lens epithelial cell response. In this study, the in vivo effectiveness of a 5 min treatment with actinomycin D and/or cycloheximid to prevent the development of capsular opacification after filling the capsular bag with a silicone polymer as an accommodating lens was studied. It was found that treating the inside of the capsular bag with a solution containing actinomycin D reduced the development of visible capsular opacification for three months. In some animals, the lens capsules were completely clear, indicating the potential of this method. Side effects of the treatment in the form of visible cornea opacification occurred and ranged from mild to severe in some animals, while in other animals no toxicity occurred. This indicates that a safe application of the cytotoxic substances is feasible. In view of the side effects and the fact that not all lens capsules of the animals treated with actinomycin D were clear, improvements in the methods used are necessary and seem to be possible. (C) 2011 Elsevier Ltd. All rights reserved

Relationship between contrast sensitivity and spherical aberration Comparison of 7 contrast sensitivity tests with natural and artificial pupils in healthy eyes

PURPOSE: To find a contrast sensitivity test that can be used clinically to evaluate interventions aimed at minimizing spherical aberration and determine the circumstances under which these tests should be performed. SETTING: Laboratory of Experimental Ophthalmology, University of Groningen, Groningen, The Netherlands. METHODS: Contrast sensitivity tests were performed using 2 experimental designs. Design 1 was with a natural pupil under mesopic and photopic conditions. Design 2 was with a 5.0 mm artificial pupil after cycloplegia under photopic conditions only. Two computerized tests (vertical sine-modulated gratings [VSG] and Holladay circular sine-modulated patterns [HACSS]) and 5 chart tests (Pelli-Robson, acuity-measuring letter charts at low contrast [2.5% and 10%], VectorVision, and edge contrast sensitivity) were used. Spherical aberration was assessed with a Hartmann-Shack wavefront analyzer. RESULTS: Forty-nine healthy subjects aged 20 to 35 years (n = 24) and 55 to 70 years (n = 25) participated. Design 2 showed a significant relationship between contrast sensitivity and spherical aberration with the HACSS at 3 cycles per degree (cpd) (P = .03) and 6 cpd (P = .01) and with the VSG at 6 cpd (P = .01). Design 1 yielded no significant relationships. CONCLUSIONS: Using an artificial pupil, a relationship between contrast sensitivity and spherical aberration was established with the VSG and HACSS tests but not with the chart tests. No test showed a relationship using natural pupils under either lighting condition. Chart tests are unsuitable for uncovering contrast sensitivity differences related to differences in spherical aberration, as typically found in healthy phakic eyes

Long-term prevention of capsular opacification after lens-refilling surgery in a rabbit model

PURPOSE: To reduce capsular opacification by a peri-surgical treatment of the lens capsule with drugs in an in vivo rabbit model. Lens-refilling surgery is a potential therapeutic intervention to treat patients with a cataract lens. The lens material is replaced with an injectable (bio)polymer that retains the natural mechanical and optical lens properties, therewith allowing accommodation. The occurrence of capsular opacification mediated by lens epithelial cells negatively affects accommodation and vision and should be avoided in this lens restoration approach. METHODS: An in vivo rabbit animal model was used with lens replacement with a silicone-based gel-like polymer and concurrent treatment of the lens epithelium with drugs. A case-study approach was applied as both drug combinations and implantation times were varied. The following drugs were investigated for their potential to prevent capsular opacification long-term: actinomycin D, methotrexate, paclitaxel and Tween-20. All were administered in a hyaluronic acid vehicle. The rabbits were clinically followed for periods up to 4 years postimplantation. Eyes, corneas and lenses were analysed post-mortem using MRI and confocal microscopy. RESULTS: Treatment combinations containing actinomycin D generally led to the least appearance of capsular fibrosis. The use of Tween-20 or paclitaxel without actinomycin D resulted in much earlier and pronounced fibrotic responses. The aspect of capsular opacification was highly variable in individual animals. Application of the drugs in a hyaluronic acid vehicle appeared to be a safe method that spared the corneal endothelium. CONCLUSION: The feasibility of long-term prevention of fibrosis over a period of more than 4 years has been demonstrated in lens refilling in the rabbit model

Development of an accommodating intra-ocular lens - In vitro prevention of re-growth of pig and rabbit lens capsule epithelial cells

Cataract surgery is routinely performed to replace the clouded lens by a rigid polymeric intra-ocular lens unable to accommodate. By implanting a silicone gel into an intact capsular bag the accommodating properties of the natural lens can be maintained or enhanced. The implantation success of accommodating lenses is hampered by the occurrence of capsular opacification (PCO) due to lens epithelial cell (LEC) growth. In order to prevent LEC proliferation, a treatment regime using actinomycin D, cycloheximide and water was developed. The effectiveness of treatment was analyzed using an in vitro, MTT-based cell culture system and an ex vivo pig eye model in which the implanted lens-in-the-bag is cultured as a whole. LEC were exposed to treatment solutions for 5 min, then the cells were allowed to recover and to re-colonize the substratum. MTT conversion by cells was transiently inhibited by cycloheximide dissolved in water and by water alone. Exposure to actinomycin D resulted in a lasting inhibition of MTT conversion and consequently cell proliferation. These in vitro data could not be fully reproduced in the ex vivo pig eye model due to essential differences between both models. Treatment with actinomycin D containing solutions, however, resulted in a nearly complete absence of cells on the capsular wall. The pig eye model is a promising approach to further evaluate the effects of peri-surgical treatment during the accommodating intra-ocular lens implantation. (c) 2006 Elsevier Ltd. All rights reserved

Prevention of capsule opacification after accommodating lens refilling:Pilot study of strategies evaluated in a monkey model

PURPOSE: To test 2 strategies to prevent capsule opacification after accommodating lens refilling in a rhesus monkey model. SETTING: Animal laboratory and laboratory of European university medical centers. DESIGN: Experimental study. METHODS: Six rhesus monkeys had refilling of the lens capsular bag. In the first strategy, before it was filled with a silicone polymer, the capsular bag was treated with noncommercial sodium hyaluronate 1.0% containing cytotoxic substances. In the second strategy, the capsular bag was filled with clinically used sodium hyaluronate 1.0% (Healon) after treatment with actinomycin-D. Slitlamp inspection was performed during a follow-up of 40 to 50 weeks. After enucleation, magnetic resonance images were obtained and confocal fluorescence imaging was performed. RESULTS: Using the first strategy, capsule opacification developed in all eyes. Using the second strategy, 1 monkey did not develop capsule opacification after a 9-month follow-up. In a second monkey, the lens capsule remained clear for 3 months, after which the hyaluronate refill material was exchanged with a silicone polymer and capsule opacification developed. Combining these results with those in a previous study, the difference in opacification between silicone and sodium hyaluronate as refilling materials was statistically significant (P CONCLUSIONS: That no capsular bag fibrosis occurred in the presence of hyaluronate suggests that the properties of hyaluronate are the reason that remaining lens epithelial cells do not develop into fibrotic cells. The choice of a suitable lens-refilling material prevents the development of capsule opacification. (C) 2014 ASCRS and ESCR

Development of a ciliary muscle-driven accommodating intraocular lens

PURPOSE: To develop a ciliary muscle-driven accommodating intraocular lens (IOL) that has a large and predictable range of variable power as a step toward spectacle independence. SETTING: Department of Physics and Medical Technology, VU University Medical Center, Amsterdam, The Netherlands. METHODS: A concept IOL that has a rotating focus mechanism and a mechanical frame that can operate within the range of ciliary muscle contraction of a typical 60-year-old human eye was designed. Prototypes were made to test the IOL's mechanical performance in an enucleated pig's eye using a laboratory lens-stretching device that mimics the action of the human ciliary muscle. Changes in focal length during stretching were measured by laser-based ray tracing and a videocamera system. To rotate the 2 lenses in the IOL with variable optical power, a frame that allows the displacement and force of the ciliary muscle to be transferred by the capsular bag was designed. RESULTS: Ray tracing showed that the modulation transfer function (MTF) of the IOL in different accommodative states did not deviate to a great extent from the MTF of a monofocal IOL. During stretching experiments, the prototype IOL achieved 8.0 diopters of accommodation. CONCLUSIONS: Evaluation of an accommodating IOL that meets the requirements for a spectacle-independent solution to presbyopia showed that the mechanical and optical designs must be further optimized to improve optical quality and functionality