Anil S. Patel

Analysis of patients with good uncorrected distance and near vision after monofocal intraocular lens implantation

PURPOSE: To analyze factors contributing to uncorrected visual acuity of at least 6/12 for distance and at least J4 for near (pseudoaccommodation) after monofocal intraocular lens (IOL) implantation. SETTING: Iladevi Cataract and IOL Research Center, Ahmedabad, India. METHODS: In a case‐controlled study of 30 eyes (30 patients) that had phacoemulsification, those with pseudoaccommodation were assigned to cases and 30 eyes (30 patients) without pseudoaccommodation were designated as controls. Controls were matched by identical best corrected visual acuity, age, and postoperative duration. Subjective refraction was done with retinoscopy. Factors analyzed included corneal astigmatism, pupil size, axial IOL movement, amplitude of accommodation, axial length (AL), and age. Corneal astigmatism was noted on topography and interpreted as against the rule (ATR) (180 ± 15 degrees), with the rule (WTR) (90 ± 15 degrees), and oblique (OB) (45/135 ± 30 degrees). Pupil size was noted on topographic display and AL and anterior chamber depth (ACD) on immersion A‐scan. The axial IOL movement was calculated as the difference in ACD after instillation of cyclopentolate 1% (Cyclopent) and subsequently pilocarpine nitrate 2% (Carpinol) at separate visits, and amplitude of accommodation was measured with static and dynamic retinoscopy. Multivariate logistic regression and odds ratio with 95% confidence intervals were determined. RESULTS: Mean spherical equivalent was −0.45 ± 0.63 diopter (D) in cases and −0.35 ± 0.83 D (P = .61) in controls. Multivariate logistic regression in cases versus controls: corneal astigmatism (ATR versus WTR and OB collectively): 10.19 [1.8,57.44], P = .009; pupil size: 0.45 [0.07,2.71], P = .38; axial IOL movement: 1.39 [0.51,0.77], P = .514; amplitude of accommodation: 2.95 [0.93,9.3], P = .065; AL: 0.55 [0.29,1.02], P = .058; and age: 0.98 [0.5,1.95], P = .963. CONCLUSION: The study suggests a significant role of ATR corneal astigmatism in good uncorrected distance and near vision after monofocal IOL implantation.

In vitro adherence of Pseudomonas aeruginosa to four intraocular lenses

Purpose: To compare the relative degrees of adherence of a clinical strain of Pseudomonas aeruginosa to the optic material of four intraocular lenses (IOLs). Setting: Center for Applied and Environmental Microbiology, Georgia State University, Atlanta, Georgia, USA. Methods: Intraocular lens optics made of poly(methyl methacrylate) (PMMA), AcrySof®‐acrylic, and silicone were included in this study. The IOLs were incubated in a minimal medium with cells of P. aeruginosa for 2 hours and 18 hours. Cells in the 2 hour experiment were prelabeled with 3H‐leucine; those in the 18 hour experiments were postlabeled. After rinsing the IOLs to remove loosely adherent cells, we determined the number of cells adhered to coded lenses from calibration curves of disintegrations per minute versus cells per square millimeter. Additional lenses were incubated with P. aeruginosa and examined with scanning electron microscopy. Results: The adherence of P. aeruginosa in order of increasing magnitude was AcrySof‐acrylic < PMMA < silicone 1 < silicone 2. The differences between all groups were statistically significant. The scanning electron microscopy observations were in general agreement with the radiolabel studies. Conclusions: The AcrySof‐acrylic IOL was less susceptible to primary adherence and 18 hour biofilm formation by P. aeruginosa than the PMMA and silicone IOLs, indicating that this material reduced pseudomonad adherence and the risk of endophthalmitis following cataract surgery.

Determining the imaging quality of intraocular lenses

Purpose: To validate the proposed optical requirements of a draft international standard for intraocular lenses (IOLs). Setting: Eight optical testing laboratories in the United States, Germany; Japan, and The Netherlands. Methods: The testing laboratories performed modulation transfer function (MTF) tests on various IOLs using a model eye and visual resolution tests in air. Each laboratory performed duplicate measurements on a set of 43 lenses that was circulated among the testing laboratories. Results: The interlaboratory tests showed that the MTF measurements using a model eye had better repeatability and reproducibility than the more common industry practice of resolution testing in air with parallel light and the United States Air Force three‐bar target. However, the two methods correlated well. The commonly applied criterion that an IOL resolve in air at least 60% of the Rayleigh cutoff spatial frequency corresponded to a minimum requirement of 0.43 MTF units at 100 mm−1 in a model eye. Conclusions: Either criterion may be applied in accordance with a proposed international standard for IOLs. The model eye method can be applied over a broader range of dioptric powers and is relevant for materials that interact with aqueous. Both tests appear to have a greater ability to detect unwanted surface aberrations than resolution testing of IOLs in a water cell using parallel light, a method described in the current American National Standards Institute standard.

Accuracy in determining intraocular lens dioptric power assessed by interlaboratory tests

Purpose: To describe a testing program conducted by a standards group as a guide for setting international tolerances for intraocular lens (IOL) dioptric power. Setting: Multicenter study. Methods: Seven biconvex, poly(methyl methacrylate) IOLs ranging in power from 10.00 through 30.00 diopters (D) were circulated among nine participating laboratories experienced in IOL optical measurements. Each laboratory performed repeated optical tests to determine dioptric power. These results were analyzed for repeatability and reproducibility in accordance with methods specified by the International Organization for Standardization. Results: Intralaboratory repeatability was less than 0.5% of the dioptric power, and interlaboratory reproducibility, when following a normalized procedure for correction and conversion, was less than 1.0% of the dioptric power. Conclusion: Tolerance limits of ±0.30 D in the range 0 to 15.00 D, ±0.40 D for 15.50 to 25.00 D, and ±0.50 D for 25.50 to 30.00 D have been proposed as an international standard for IOLs. The contribution of IOL power error within the limits of the standard are estimated to contribute less than 1.0% to the total error in postoperative refractive prediction.

New approach to evaluate retinal protection by intraocular lenses against age-related lipofuscin accumulation-mediated retinal phototoxicity.

PURPOSE: To present a new approach for evaluating intraocular lenses (IOLs) for retinal protection from age‐related lipofuscin accumulation–mediated phototoxicity. SETTING: Alcon Laboratories Inc., Fort Worth, Texas, USA, and Cardiff University, Cardiff, United Kingdom. METHODS: Age‐related lipofuscin accumulation–mediated action spectra for retinal phototoxicity in an aphakic eye were created for this evaluation. Transmission curves for 6 IOLs and for cornea and spectral radiant power distribution for sunlight and 2 lamps were used. Pseudophakic action spectra and retinal phototoxicity for 3 wavelength ranges and 3 ages were computed. The percentage protection of each IOL was computed as the reduction in phototoxicity relative to the aphakic eye. RESULTS: Retinal phototoxicity increased 3.66 times from the third to ninth decade of age. The comparative retinal phototoxicity and retinal protection provided by IOLs were dependent on the light source and range of wavelength; however, unlike phototoxicity, retinal protection was independent of age. The 420 to 480 nm range was the most useful for discriminating protection by IOLs. CONCLUSIONS: Retinal phototoxicity significantly increased with age; however, the retinal protection by IOLs was independent of age. The interaction between the transmission curve of IOLs and light sources required inclusion of widely used lamps besides sunlight for evaluation of IOLs. For the 420 to 480 nm wavelength range, the 3 light sources clearly discriminated the protection provided by IOLs. The AcrySof Natural IOL (Alcon) provided the highest protection consistently for the tested light sources.

Evaluation of an unused 1952 Ridley intraocular lens

PURPOSE To evaluate an unused 1952 historic Ridley intraocular lens (IOL) brought to Bombay, India, in 1952 from an Oxford Ophthalmologic Conference in England and given to 1 of the authors during his residency. SETTING Alcon Laboratories, Fort Worth, Texas, USA. METHODS The Ridley IOL was evaluated at Alcon Laboratories, Inc., using the established procedures of its Intraocular R&D Laboratories. Various optical and physical aspects of the Ridley lens were evaluated including (1) dimensions, (2) weight, (3) power, (4) resolution efficiency and modulation transfer function (MTF), (5) surface sphericity by interferometry, (6) ultraviolet (UV)-visible transmission characteristic, (7) attenuated total reflectance (ATR)-Fourier transform infrared reflectance spectrum, and (8) cosmetics by visual inspection using light microscopy. RESULTS This 8.5 mm diameter, 2.4 mm thick, 23 diopter biconvex IOL weighed 108 mg. The ATR spectrum, UV-visible transmission, and refractive index confirmed its poly-(methyl methacrylate) material. The 0.56 MTF value at 100 line pairs/mm, per the International Standards Organization--IOL Optics Standard, and 93% resolution efficiency in water, per the American National Standard Institute IOL Optics Standard, revealed the IOLs excellent optics. This was confirmed by 0.278 wave root mean square surface figure as measured by Zygo interferometer using a 633 nm wavelength. Visual inspection revealed rough edges with sharp corners and some surface scratches. Early clinical experience with Ridley IOLs in Bombay, India, is briefly given. CONCLUSION The Ridley IOL had excellent optical quality, meeting the requirements of current IOL optics standards. The selection of its dimensions was guided by the human crystalline lens, and the Ridley IOL was half as bulky. Although its clinical results were mixed, successful cases inspired subsequent improvements, leading to modern, highly satisfactory IOLs. This IOL represented a revolutionary innovation in ophthalmology.

Ocular biocompatibility testing of intraocular lenses: a 1 year study in pseudophakic rabbit eyes.

PURPOSE To evaluate the appropriate duration for conducting ocular biocompatibility studies with an intraocular lens (IOL) in the pseudophakic rabbit model. SETTING Alcon Laboratories, Inc., Fort Worth, Texas, USA. METHODS A single-piece biconvex poly(methyl methacrylate) (PMMA) IOL was implanted in the capsular bag of 18 eyes of New Zealand white rabbits; 8 eyes received sham surgeries. Rabbits were monitored clinically and then sacrificed 6 or 12 months after surgery for histopathological examination of ocular tissues. RESULTS Biomicroscopic examination revealed mild ocular changes in all surgical eyes during the first 3 months postoperatively. After that, there was a high incidence of posterior synechias, flare, and posterior capsule opacification (PCO) in eyes with PMMA IOLs. Posterior synechias and flare scores remained mild to moderate throughout the study, whereas PCO severity increased over time. Similar findings were observed in sham eyes. In addition, several eyes with PMMA IOLs developed IOL dislocation, hyphema, iris bombe, and a fibrous membrane covering the IOL. No discernible differences in biomicroscopic scores were observed in eyes at 6 or 12 months. Intraocular pressures and morphology of the corneal endothelium were normal in both groups. Results from histopathological analysis of the ocular tissues were consistent with observations from the biomicroscopic examinations. CONCLUSION The results suggest that IOL implantation studies in the pseudophakic rabbit eye should be conducted for 3 or fewer months. Regulatory guidelines requiring longer ocular implantation studies should be revised to reflect the inherently rapid and extensive ocular response in the rabbit model.

Safety of sleep regulation after cataract surgery and complexity of the photoentrainment of circadian rhythm

Dexamethasone implant as an effective treatment option for macular edema in Irvine-Gass syndrome I read with interest the article by Mayer et al. The authors studied a cohort of 23 patients diagnosed with pseudophakic cystoid macular edema (CME) and managed it successfully with an intravitreal dexamethasone implant. However, certain aspects of this interesting study need further evaluation. In Figure 4, the authors compare visual gain to the duration of the CME. It appears as though the final visual acuity is independent of the duration of the CME, although the visual gain might be slow initially in longstanding cases. This might be explained by the fact that most of the patients with a disease duration of more than 6 months had a baseline macular thickness of more than 500 mm (Table 1). It would be interesting to know how baseline macular thickness correlated with the duration of the CME. Overall, 9 patients required retreatment, mostly after 3 or 4 months of therapy (Table 2), when the effect of the implant starts declining. However, all the retreated patients were stable at 1 year from the start of the study, with a macular thickness below 300 mm in all 23 patients. Hence, unlike the vascular endothelial growth factor–dependent macular edema, where delayed onset treatment might lead to poor response to therapy, visual gain inpseudophakicCMEappears to be independent of treatment delay. This reflects the favored hypothesis for the cause of Irvine-Gass syndrome being inflammatory cytokines and it being selflimiting usually, as also mentioned by the authors. To further strengthen this argument, I suggest a separate analysis for patients requiring retreatment, especially in terms of their baseline characteristics. I hope this discussion adds to the valuable results in the study.

Additional basics for mesopic contrast sensitivity testing and need for use of artificial pupil

Combined transepithelial phototherapeutic keratectomy and corneal collagen crosslinking for ectatic disorders: Cretan protocol In the introduction of their recent study of transepithelial phototherapeutic keratectomy (PTK) combined with implantation of a single inferior intrastromal corneal ring segment (ICRS) and corneal collagen crosslinking (CXL) in keratoconus, Yeung et al. reported that Kanellopoulos used transepithelial PTK to remove the corneal epithelium before topographyguided photorefractive keratectomy (PRK) and CXL in patients with keratoconus. However, in the article by Kanellopoulos, the corneal epithelium was mechanically removed with the use of a 20% alcohol solution. We think it is necessary to point out that in 2010, we first described corneal epithelial removal using transepithelial PTK during CXL. Moreover, our fellow article regarding combined transepithelial PTK and CXL for progressive keratoconus is, to our knowledge, the first and the only prospective study that deals with comparative outcomes of corneal epithelial removal techniques during CXL and indicates the benefits of using transepithelial PTK (Cretan protocol). Our study, which was a prospective comparative analysis of well-matched groups, showed that transepithelial PTK during CXL results in better visual and refractive outcomes than mechanical epithelial debridement. Removal of the corneal epithelium using transepithelial PTK during CXL is a relatively new combined technique, and we believe it should be performed in any case of CXL for better visual and refractive outcomes, especially in cases in which PRK with CXL cannot be performed due to low corneal thickness.