The importance of the cornea to the ocular structure and visual system is often overlooked because of the cornea's unassuming transparent nature. The cornea lacks the neurobiological sophistication of the retina and the dynamic movement of the lens; yet, without its clarity, the eye would not be able to perform its necessary functions. The complexity of structure and function necessary to maintain such elegant simplicity is the wonder that draws us to one of the most important components of our visual system.

Anatomy and physiology of the cornea

Ocular and Systemic Pseudoexfoliation Syndrome

PURPOSE: The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. METHODS: Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. RESULTS: Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL. This improvement occurred without an apparent loss in depth of focus. CONCLUSION: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients. [J Refract Surg 2002;18: 683-691] T

A new intraocular lens design to reduce spherical aberration of pseudophakic eyes.

We studied the age dependence of the relative contributions of the aberrations of the cornea and the internal ocular surfaces to the total aberrations of the eye. We measured the wave-front aberration of the eye with a Hartmann-Shack sensor and the aberrations of the anterior corneal surface from the elevation data provided by a corneal topography system. The aberrations of the internal surfaces were obtained by direct subtraction of the ocular and corneal wave-front data. Measurements were obtained for normal healthy subjects with ages ranging from 20 to 70 years. The magnitude of the RMS wave-front aberration (excluding defocus and astigmatism) of the eye increases more than threefold within the age range considered. However, the aberrations of the anterior corneal surface increase only slightly with age. In most of the younger subjects, total ocular aberrations are lower than corneal aberrations, while in the older subjects the reverse condition occurs. Astigmatism, coma, and spherical aberration of the cornea are larger than in the complete eye in younger subjects, whereas the contrary is true for the older subjects. The internal ocular surfaces compensate, at least in part, for the aberrations associated with the cornea in most younger subjects, but this compensation is not present in the older subjects. These results suggest that the degradation of the ocular optics with age can be explained largely by the loss of the balance between the aberrations of the corneal and the internal surfaces.

Contribution of the cornea and internal surfaces to the change of ocular aberrations with age

https://scholarlypublications.universiteitleiden.nl/access/item%3A3006538/view

Non-syndromic retinitis pigmentosa

Purpose: To determine the principal risk factors for corneal endothelial injury during phacoemulsification. Setting: Hayashi Eye Hospital, Fukuoka, Japan. Methods: We prospectively investigated 859 consecutive eyes of 800 patients who had had phacoemulsification surgery. The percentage of corneal endothelial cell loss at 3 months after surgery was quantitated using specular microscopy. The firmness of the nucleus was graded by Emery's classification prior to surgery. We selected nine variables that could be associated with endothelial injury. The univariate associations between the endothelial cell loss and these variables were evaluated using simple correlation coefficients. A multiple linear regression analysis was performed to identify independent predictors of endothelial cell loss. Results: In the simple regression analysis, older age, small pupil diameter, high nucleus grade, large nucleus, greater infusion volume, type of IOL implanted, and a greater amount of total emitted ultrasound energy were univariately associated with endothelial cell loss. In the multiple linear regression analysis, the best final model (R2 = 0.42) identified high nucleus grade, greater infusion volume, type of IOL implanted, and large nucleus as independent predictors of endothelial cell loss. Conclusion: Both univariate and multivariate analyses identified the firmness of the nucleus as the most significant risk factor for endothelial cell loss. Therefore, mechanical contact with nuclear fragments is considered the principal cause of endothelial injury.

Risk factors for corneal endothelial injury during phacoemulsification

Changes in anterior chamber angle width and depth after intraocular lens implantation in eyes with glaucoma.

Purpose: To examine the effect of cataract surgery on intraocular pressure (IOP) control in eyes with angle-closure glaucoma (ACG) and open-angle glaucoma (OAG). Setting: Hayashi Eye Hospital, Fukuoka, Japan. Methods: This study included 74 eyes with ACG and 68 eyes with OAG having cataract surgery. The IOP was measured and the number of glaucoma medications recorded preoperatively, 1 month postoperatively, and then every 3 months. The IOP control in the 2 groups was compared using survival analysis, with failure criteria being an IOP greater than 21 mm Hg, addition of medications, or the need for additional glaucoma surgery. Results: The mean IOP and number of medications decreased significantly after surgery in both groups ( P P = .0012). The IOP was controlled without medication in 30 eyes (40.5%) in the ACG group and 13 (19.1%) in the OAG group; the difference between groups was significant ( P = .0055). Conclusions: Cataract surgery substantially reduced IOP and the number of medications required for IOP control in glaucomatous eyes. Specifically, cataract extraction normalized the IOP in most eyes with ACG.

Effect of cataract surgery on intraocular pressure control in glaucoma patients.

Objective: To quantitatively compare the extent of posterior capsule opacification (PCO) after polymethylmethacrylate (PMMA), silicone, and soft acrylic intraocular lens implantation. Patients and Methods: A total of 240 eyes from 240 patients undergoing implant surgery were randomized into 3 groups based on the type of lens implanted: PMMA, silicone, and soft acrylic. The density value of PCO in 185 eyes was quantitated approximately 2 years after surgery by a new measurement method using the Scheimpflug videophotography system. Results: Twenty-one eyes (30.4%) in the PMMA group, 4 (5.7%)inthesiliconegroup,and2(2.7%)intheacrylicgroup hadalreadyundergoneNd:YAGlaserposteriorcapsulotomy. The mean ± SD PCO values were 26.3 ± 12.2 computercompatible tape steps (CCT) in the PMMA group, 12.0 ± 8.3 CCTinthesiliconegroup,and16.0 ± 10.3CCTintheacrylic group. The PCO value in the PMMA group was significantly greater than that in the silicone or acrylic group (P,.001). The visual acuity loss in the PMMA group was also greater than that in the silicone or acrylic group (P,.001). Conclusion: Based on the PCO value and capsulotomy rate, the PCO was more extensive with the PMMA lens than with either the silicone or soft acrylic lens, which led to visual acuity loss.

https://jamanetwork.com/journals/jamaophthalmology/articlepdf/264513/ecs8283.pdf

Ken Hayashi

Papers

Risk factors for corneal endothelial injury during phacoemulsification

Changes in anterior chamber angle width and depth after intraocular lens implantation in eyes with glaucoma.

Effect of cataract surgery on intraocular pressure control in glaucoma patients.

Quantitative Comparison of Posterior Capsule Opacification After Polymethylmethacrylate, Silicone, and Soft Acrylic Intraocular Lens Implantation

Possible predisposing factors for in-the-bag and out-of-the-bag intraocular lens dislocation and outcomes of intraocular lens exchange surgery.