ABSTRACT
CONTEXT: Contrast sensitivity (CS) function is one of the most important tests available for evaluating visual impairment. Multiple sclerosis (MS) can produce highly selective losses in visual function and psychophysical studies have demonstrated CS deficits for some spatial frequencies. AIMS: This work studies the differences in CS between a group of controls and a group of MS patients, focusing on the location of the maximum sensitivity peak, shape of the curve, and determination of the most affected spatial frequencies. MATERIALS AND METHODS: Using a sinusoidal stimulus the authors assessed CS function in 28 subjects with definitive relapsing remitting MS, and in 50 controls with acuities of 20/25 or better. The peaks of the CS curves were studied by fitting third degree polynomials to individual sets of data. RESULTS: Compared with the control group, the CS function curve for MS subjects showed more deficits in extreme points (low- and high-spatial frequencies). Our results display significant CS losses, at the high-frequencies band level, in the beginning of the disease. When the disease progresses and the disabilities appear, there are greater losses at the low-frequencies band level. In average, the CS curve peaks for the MS group were shifted in relation to the control group. CONCLUSIONS: CS losses in the MS group suggest an association with ageing and disability level in the expanded disability status scale. The position of the CS function peak is influenced by MS, age, and degree of disability.
Subject(s)
Contrast Sensitivity/physiology , Disability Evaluation , Multiple Sclerosis, Relapsing-Remitting/complications , Vision Disorders/physiopathology , Adult , Age Factors , Disease Progression , Female , Humans , Male , Middle Aged , Multiple Sclerosis, Relapsing-Remitting/physiopathology , Multiple Sclerosis, Relapsing-Remitting/rehabilitation , Photic Stimulation , Prognosis , Vision Disorders/etiology , Vision Disorders/rehabilitation , Visual AcuityABSTRACT
A computer model using finite ray tracing methods was developed to simulate a videokeratoscope analysing an average cornea. Different faceplate designs were tested using five points on the faceplate subtending angles at the corneal vertex between 15 degrees and 75 degrees in 15 degrees intervals. Image quality was assessed by adding the geometrical blurs of the five image points. Differences (error) between true sagittal radius of curvature, and sagittal radius of curvature calculated by the van Saarloos algorithm, were calculated for selected surfaces at the same corneal points. Differences equal to or bigger than 0.02 mm were regarded as clinically significant. The faceplate surface that provided the sharpest image for an average cornea was a cylinder with the base 120 mm away from the corneal vertex and a diameter of 26 mm. Changing the faceplate design results in clinically significant differences for an average cornea. Image quality is not proportional to corneal surface reconstruction accuracy.
