PURPOSE To quantify the error introduced by videokeratographic corneal topography devices in using a paraxial formula to calculate power over the entire corneal surface, including areas removed from the central paraxial region where the formula is known to be invalid. METHODS Corneal refractive power and two paraxial power approximations were computed as a function of distance from the apex f...

The cornea is the anterior most surface of the eye and plays a critical role in vision. A thin fluid layer, the tear film, coats the outer surface of the cornea and serves to protect, nourish, and lubricate the cornea. At the same time, the tear film is responsible for creating a smooth continuous surface, where the majority of refraction takes place in the eye. A significant component of visio...

PURPOSE To develop the instrumentation and software for wide-angle corneal topography using a Placido-based videokeratographer. The objective is to allow the measurement of a greater area of the cornea using a simple adaptation to the Placido mire. METHODS Using the traditional Placido disc of a commercial corneal topographer, 9 LEDs (Light Emitting Diodes) were installed on the conic mire so...

Purpose. To thoroughly analyze corneal deformation responses curves obtained by Ocular Response Analyzer (ORA) testing in order to improve subclinical keratoconus detection. Methods. Observational case series of 87 control and 73 subclinical keratoconus eyes. Examination included corneal topography, tomography, and biomechanical testing with ORA. Factor analysis, logistic regression, and receiv...

Objective Screening of school children for scoliosis is an orthopedic examination that has a direct effect on the health of these children. Screening can be performed using various methods. Since 1983, in our prefecture, we have used Moire topography for screening. The purpose of this study was to evaluate the prevalence rate of scoliosis diagnosed by screening school children using Moire topog...

OBJECTIVE To evaluate the effects of the intrastromal corneal ring, a device developed to reduce myopia, on corneal asphericity in a large set of eye bank eyes. METHODS Forty-one deturgesced eye bank eyes were implanted with intrastromal corneal rings of five different thicknesses, ranging from 0.25 mm to 0.45 mm. Corneal asphericity, before and after implantation, was examined using two diff...

Background: The possible impact of corneal thickness, curvature, and size on the measurement of endothelial cell density (ECD) has largely been ignored in the normal eye. The aim of this study was to investigate the possible impact of the main corneal parameters on the analysis of ECD values at the central, superior, and temporal parts of the corneal surface. Methods: All 75 participants (52 fe...

PURPOSE To evaluate long-term results of sequential customized therapeutic keratectomy (SCTK) in highly aberrated corneas with apical scars consequent to hyperopic excimer laser refractive surgery. METHODS Fifteen eyes of 12 patients treated with SCTK for a corneal apical scar after hyperopic excimer laser refractive surgery were retrospectively evaluated. SCTK is a sequence of custom therape...

PURPOSE Although visual inspection of corneal topography maps by trained experts can be powerful, this method is inherently subjective. Quantitative classification methods that can detect and classify abnormal topographic patterns would be useful. An automated system was developed to differentiate keratoconus patterns from other conditions using computer-assisted videokeratoscopy. METHODS Thi...

PURPOSE To compare the relative advantages and disadvantages of four different representations of corneal power--identified as instantaneous, axial, position, and refractive--based on curvature, slope, coordinate position, and focal properties, respectively. METHOD The four types of corneal power were evaluated by examining their interrelationship for 12 hypothetical corneal shapes chosen to ...