Katherine Oliver

Corneal Optical Aberrations Induced by Photorefractive Keratectomy

BACKGROUND Photorefractive keratectomy causes marked alteration to anterior corneal topography, and is likely to induce major changes to the optical aberrations of the eye. METHODS Six diopters (D) of myopia correction was attempted on one eye of 50 patients, randomly allocated to one of three different treatments: 5-mm or 6-mm single ablation zone, or a double ablation (multizone; -5.00 D correction over 4.6 mm and -1.00 D over 6 mm). Topographic data was used to estimate corneal aberration coefficients. These were compared for effect of ablation zone, before and 1 year after photorefractive keratectomy. The coefficients were used to derive modulation transfer functions for the anterior corneal surface. RESULTS Corneal spherical aberrations and coma-like aberrations both increased significantly following photorefractive keratectomy (p < 0.001). The mean spherical aberration coefficient increased from 0.36 +/- 0.11 before, to 0.91 +/- 0.37 after treatment, while the mean coma-like aberration coefficient changed from 0.28 +/- 0.16 before, to 0.60 +/- 0.31 after treatment. Ablation zone form had a significant effect on spherical aberration (p = 0.030), but not for coma (p = 0.96). The spherical aberration coefficient increased least for the 6-mm ablation (by 0.38 +/- 0.17), compared with the 5-mm ablation (0.69 +/- 0.45) and the multizone (0.62 +/- 0.38). Corneal modulation transfer functions were reduced significantly following the photorefractive procedure. The effect was greatest for large pupil diameters and for spatial frequencies between 2 and 15 cycles per degree. CONCLUSIONS Corneal modulation transfer function calculations suggest that a significant loss of visual performance should be anticipated following photorefractive keratectomy, the effect being greatest for large pupil diameters. Results for three ablation zones show that induced aberrations are least for the largest (6 mm) ablation zone.

An In Vivo Investigation of the Structures Responsible for Corneal Haze after Photorefractive Keratectomy and Their Effect on Visual function

PURPOSE To make serial measurements of corneal haze and microscopic anatomy after photorefractive keratectomy (PRK) and compare the results with visual function measured at the same time points in the same single group of human subjects. METHODS Ten patients underwent -6.00-diopter, 6-mm PRK. The patients were reviewed frequently for 12 months. Corneal haze was measured objectively in two ways: (1) an opacification index was determined from the variance in digitized retroillumination images; and (2) light reflected and scattered back from the cornea was assessed by gray-scale analysis of video slit images. In vivo confocal microscopy recorded the anatomic changes occurring in the cornea, and computer analysis of the images quantified the keratocytes and subepithelial deposit. Visual performance was assessed by Snellen visual acuity, contrast sensitivity, and glare-induced visual dysfunction. RESULTS In the first week, epithelial irregularity resulted in a transient reduction in all aspects of visual function. In the first month, keratocyte disturbances reduced contrast sensitivity at high frequencies and produced glare. Over the next couple of months, the subepithelial deposit resulted in a more prolonged loss of contrast sensitivity at low frequencies and glare-induced visual dysfunction due to the scattering of light. In several patients, these visual defects persisted after 1 year. CONCLUSIONS Epithelial and keratocyte disturbances only transiently affect visual function. The subepithelial deposit is more persistent and can have a lasting effect on visual performance. Therefore, attempts to improve the visual outcome of PRK must be aimed at controlling the synthesis of subepithelial material.

Anterior Corneal Optical Aberrations Induced by Photorefractive Keratectomy for Hyperopia

PURPOSE Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye. METHODS Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests. RESULTS Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error. CONCLUSIONS The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.

Corneal optics from videokeratographs

Recent developments in measuring corneal topography make possible an improved understanding of corneal optics. It is shown, using a wavefront analysis, that optical quantities of interest follow from knowledge of sagittal depths of a cornea, and that sagittal depths are provided by or readily found from the output of commercially available instruments. The errors for normal corneas are expected to be quite small based on measurements on calibration spheres and ellipsoids. As an example the optical consequences of a peripheral asymmetry are estimated for a particular normal cornea.

Optical consequences of asymmetries in normal corneas.

A survey of videokeratographs of normal corneas shows many with substantial peripheral asymmetries. For sufficiently large pupils (5.5 mm in this study) these asymmetries lead to coma-like axial aberrations large enough to produce measurable losses in vision in a number of cases. Starting from the output of a videokeratographic instrument, a method of estimating the optical effects of corneal asymmetries using Zernike circle polynomials is outlined. It is further shown that in a first approximation corneal asymmetries can be identified with the primary aberration coma and that this aberration is approximately due to a uniform gradient of refractive power across the cornea. Calculations for a representative case predict that a significant improvement in modulation transfer would follow from correction of this aberration.

Effect of hyperopic photorefractive keratectomy on corneal sensitivity: A longitudinal study

PURPOSE To investigate corneal sensitivity after photorefractive keratectomy (PRK) for low hyperopia, as measured with a non-invasive stimulus. METHODS Two experimental groups were recruited: a control group of 17 patients (mean age 61.65 years) who underwent no treatment, and a PRK group of 11 patients (mean age 58.64 years) who underwent one of three attempted hyperopic corrections: +2.00 D (two patients), +3.00 D (four patients), +4.00 D (five patients). Corneal sensitivity was assessed centrally and peripherally, at temporal, medial, and inferior locations, approximately 1 mm from the limbus, using the Non-Contact Corneal Aesthesiometer (NCCA). Measurements were taken at each location for the control group and at preoperative, and postoperative weeks 1 and 2, 1, 3, and 6 months for the PRK group. RESULTS Comparison of control and PRK groups (preoperative sensation threshold) (t-test): central P=.715, temporal P=.719, medial P=.943, inferior P= .920. Comparison of longitudinal changes in PRK group (one-way ANOVA): central P=.612, temporal P=.997, medial P=.981, inferior P=.993. CONCLUSIONS Using the Non-Contact Corneal Aesthesiometer, no significant difference was found between the control and PRK groups for preoperative sensation thresholds, and no significant change in corneal sensitivity was found between any of the test time periods at any of the four corneal test locations for the PRK group.

Narrow Spectrum Kinase Inhibitors Demonstrate Promise for the Treatment of Dry Eye Disease and Other Ocular Inflammatory Disorders

Purpose The purpose of this study is to determine the potential of narrow spectrum kinase inhibitors (NSKIs) to treat inflammatory eye disorders. Methods Human conjunctival epithelial (HCE) cells were retrieved from subjects via impression cytology. Real-time quantitative PCR (qPCR) was performed on HCE cells to determine gene expression of NSKI kinase targets and proinflammatory cytokines in dry eye disease (DED) patients versus healthy controls. qPCR also assessed p38α expression in hyperosmolar-treated Chang conjunctival epithelial cells. Interaction of NSKI TOP1362 with the kinases was evaluated in ATP-dependent Z-LYTE and competition binding assays. Anti-inflammatory activity was assessed in human peripheral blood mononuclear cells and primary macrophages. In an endotoxin-induced uveitis (EIU) study, lipopolysaccharide (LPS) was administered intravitreally to Lewis rats. TOP1362, dexamethasone, or vehicle was administered topically, and inflammatory cytokine levels were measured 6 hours after LPS injection. Results HCE cells from DED patients showed significantly increased expression of p38α, spleen tyrosine kinase (Syk), Src, lymphocyte-specific protein tyrosine kinase (Lck), interleukin one beta (IL-1β), interleukin eight (IL-8), monocyte chemotactic protein-1 (MCP-1), and matrix metalloproteinase-9 (MMP-9). TOP1362 strongly inhibited the kinase targets p38α, Syk, Src, and Lck, blocked the rise in p38α expression in hyperosmolar Chang cells, and potently reduced inflammatory cytokine release in cellular models of innate and adaptive immunities. In the EIU model, TOP1362 dose-dependently attenuated the LPS-induced rise in inflammatory cell infiltration and ocular cytokine levels with efficacy comparable to that of dexamethasone. Conclusions TOP1362 is a potent inhibitor of kinases upregulated in DED and markedly attenuates proinflammatory cytokine release in vitro and in vivo, highlighting the therapeutic potential of NSKIs for treating ocular inflammation, such as that observed in DED.

Automatic Tear Film Segmentation Based on Texture Analysis and Region Growing

Dry eye syndrome is a prevalent disease characterized by symptoms of discomfort and ocular surface damage. It can be identified by several types of diagnostic tests, one of which consists in capturing the appearance of the tear film by means of the Doane interferometer. Previous research has demonstrated that this manual test can be automated, with the benefits of saving time for experts and providing unbiased results. However, most images are made up of a combination of different patterns which makes their classification into one single category per eye not always possible. In this sense, this paper presents a first attempt to segment tear film images based on the interference patterns, and so to detect multiple categories in each individual subject. The adequacy of the proposed methodology was demonstrated since it provides reliable results in comparison with the practitioners’ annotations.

Effect of tear supplements on signs, symptoms and inflammatory markers in dry eye

HighlightsAll three tear supplements significantly reduce symptoms of dry eye disease.All three tear supplements significantly improve tear film stability.CGC drops showed the greatest apparent reduction in inflammatory markers.Results suggest mismatch between symptoms and inflammatory markers. Purpose: Three tear supplements were compared for their effects on the signs, symptoms and inflammatory status of subjects with dry eye disease. Assessments were made before and after both 2 and 4 weeks of treatment. Methods: In this masked, randomized, 3‐way crossover trial, eighteen dry eye subjects were recruited. At each visit, symptoms, tear evaporation rate, stability and osmolarity were measured and tear samples were analyzed for 7 inflammatory markers, using multiplex immunoassays. The 3 treatments included carboxymethylcellulose‐glycerine‐castor oil (CGC), carboxymethylcellulose (CMC) and hydroxypropyl guar (HPG). The CGC and HPG drops are emulsified lipids; CGC also contains osmoprotectants. The CMC drop is a standard aqueous polymeric supplement. Results: Significant improvements were seen in symptoms (OSDI) and tear stability (NITBUT) with all 3 treatments at 4 weeks. At 4 weeks post‐CGC, 6 out of 7 biomarkers demonstrated a >25% reduction (in 40% of subjects). The same reduction (>25%) was seen in 10% of the subjects for CMC and in none of the subjects for HPG. No significantly different change to either evaporation rate or tear osmolarity was found following any of the three treatments. Conclusions: In this study, the CGC treatment resulted in the greatest reduction in ocular biomarkers of inflammation, while all 3 treatments reduced symptoms and improved tear stability. These results indicate that subject‐perceived symptomatic improvements are not necessarily associated with a reduction in objective measures of inflammation.

Care solution effects on contact lens in vivo wettability

The aim of the study was to evaluate the effect of care solutions on contact lens in vivo wettability using Doanes interferometric technique.