A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The aim of the DEWS Definition and Classification Subcommittee was to provide a contemporary definition of dry eye disease, supported within a comprehensive classification framework. A new definition of dry eye was developed to reflect current understanding of the disease, and the committee recommended a three-part classification system. The first part is etiopathogenic and illustrates the multiple causes of dry eye. The second is mechanistic and shows how each cause of dry eye may act through a common pathway. It is stressed that any form of dry eye can interact with and exacerbate other forms of dry eye, as part of a vicious circle. Finally, a scheme is presented, based on the severity of the dry eye disease, which is expected to provide a rational basis for therapy. These guidelines are not intended to override the clinical assessment and judgment of an expert clinician in individual cases, but they should prove helpful in the conduct of clinical practice and research.

The definition and classification of dry eye disease: Report of the definition and classification subcommittee of the international Dry Eye WorkShop (2007)

50 Years of Image Analysis

t hereportoftheepidemiologySubcommit - teeofthe � 2007� dryeyeWorkShopsummarizescurrent� knowledgeontheepidemiologyofdryeyedisease, �providing� prevalenceandincidencedatafromvariouspopulations.� It� stressestheneedtoexpandepidemiologicalstudiestoad- ditionalgeographicregions, � toincorporatemultipleraces� andethnicitiesinfuturestudies, �andtobuildaconsensus� ondryeyediagnosticcriteriaforepidemiologicalstudies.� recommendationsaremaderegardingseveralcharacteristics� ofdryeyequestionnairesthatmightbesuitableforusein� epidemiologicalstudiesandrandomizedcontrolledclinical� trials.�riskfactorsfordryeyeandmorbidityofthedisease� areidentified, �andtheimpactofdryeyediseaseonqualityof� lifeandvisualfunctionareoutlined. �Suggestionsaremadefor� furtherprospectiveresearchthatwouldleadtoimprovement� ofbotheyeandgeneralpublichealth.

The epidemiology of dry eye disease: Report of the epidemiology subcommittee of the international Dry Eye WorkShop (2007)

This paper presents a general theory for the remote estimation of the point-of-gaze (POG) from the coordinates of the centers of the pupil and corneal reflections. Corneal reflections are produced by light sources that illuminate the eye and the centers of the pupil and corneal reflections are estimated in video images from one or more cameras. The general theory covers the full range of possible system configurations. Using one camera and one light source, the POG can be estimated only if the head is completely stationary. Using one camera and multiple light sources, the POG can be estimated with free head movements, following the completion of a multiple-point calibration procedure. When multiple cameras and multiple light sources are used, the POG can be estimated following a simple one-point calibration procedure. Experimental and simulation results suggest that the main sources of gaze estimation errors are the discrepancy between the shape of real corneas and the spherical corneal shape assumed in the general theory, and the noise in the estimation of the centers of the pupil and corneal reflections. A detailed example of a system that uses the general theory to estimate the POG on a computer screen is presented.

General theory of remote gaze estimation using the pupil center and corneal reflections

A review of keratoconus: Diagnosis, pathophysiology, and genetics.

AIMS: A blind, randomised, prospective, bilateral study to investigate the efficacy of riboflavin/ultraviolet A corneal collagen cross-linkage to halt the progression of keratoconus. METHODS: 24 patients with early/moderate bilateral keratoconus with recent progression were recruited. One eye was randomly assigned to undergo collagen cross-linkage following epithelial removal with riboflavin 0.1% and ultraviolet A (370 nm at 3 mW/cm(2)). The other remained untreated as a control. The follow-up was 18 months in 22 patients. RESULTS: At 18 months, Orbscan II 3 mm, 5 mm keratometry and simulated astigmatism and cone apex power and wave-front measurements (Keraton Scout), including root mean square, coma and pentafoil showed significant reductions from baseline in treated compared with untreated eyes (p=0.04). In treated eyes at 18 months, the best spectacle-corrected acuity improved (p=0.01), and Orbscan II-simulated keratometry (p<0.001), 3 mm keratometry (p=0.008), simulated astigmatism (p=0.007), cone apex power (p=0.002), root mean square, coma, spherical aberration, secondary astigmatism and pentafoil (p=0.05) decreased from baseline. One treated eye experienced transient recurrent corneal erosions; otherwise there were no complications attributable to the treatment. CONCLUSIONS: Corneal collagen cross-linkage appears to be an effective and safe modality to halt the progression of keratoconus. Improvements in visual and topographic parameters are seen in some eyes.

https://bjo.bmj.com/content/bjophthalmol/95/11/1519.full.pdf

A randomised, prospective study to investigate the efficacy of riboflavin/ultraviolet A (370 nm) corneal collagen cross-linkage to halt the progression of keratoconus

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.

Corneal optical aberrations induced by photorefractive keratectomy.

A long-term study of photorefractive keratectomy; 12-year follow-up.

Objective: To determine the effects of the ablation diameter on the outcome of excimer laser photorefractive keratectomy. Design: Eighty patients were randomized to either a 5.00-mm or a 6.00-mm treatment group and within these groups underwent either a −3.00-diopter (D) ora −6.00-D correction based on their preoperative refraction. A Summit Omnimed excimer laser was used throughout the study. Results: In eyes treated with a 6.00-mm-diameter ablation, the initial hyperopic shift was reduced, with significant differences at 1 week with −3.00-D corrections and at 1 and 4 weeks with −6.00-D corrections (P Conclusions: Treatment with 6.00-mm ablation diameters precipitated less initial overcorrection, greatly improved the predictability of photorefractive keratectomy, and was associated with a reduction in complications impairing postoperative visual performance.

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=OPHTH&articleId=641095&pdfFileName=archopht_113_4_026.pdf

David P.S. O'Brart

Papers

A review of keratoconus: Diagnosis, pathophysiology, and genetics.

A randomised, prospective study to investigate the efficacy of riboflavin/ultraviolet A (370 nm) corneal collagen cross-linkage to halt the progression of keratoconus

Corneal optical aberrations induced by photorefractive keratectomy.

A long-term study of photorefractive keratectomy; 12-year follow-up.

The Effects of Ablation Diameter on the Outcome of Excimer Laser Photorefractive Keratectomy: A Prospective, Randomized, Double-Blind Study