Abstract
Abstract: :
Background: we are developing a motion displacement threshold (MDT) test for the diagnosis of early glaucoma using line stimuli moving perpendicular to the orientation of the retinal nerve fiber layer. Purpose: to assess the effect of refractive blur on MDT. Methods: A video display under PC control was used to present a horizontal line stimulus in the nasal field at -27,3 degrees at a test distance of 30cm. Contrast was 84%. The right eye of two experienced normal subjects (46 and 30 years) was tested. A central target was fixated and lens strengths of (i) +/- 0,2,4, and 6DSph and (ii) +/- 0,2,4, and 6DCyl at 90/180 degree axis (additional to peripheral refraction determined by retinoscopy under mydriasis) were centered at -27,3 degrees. The line stimulus (lengths 43, 86 or 128 min arc) was programmed to pass through 5 presentations of 7 randomized displacements (0-24 min arc). Stimulus presentation consisted of 3 oscillations, duration 200 msec per cycle. Each parameter was tested 3 times, frequency of seeing curves (FOS) were obtained and 50% seen threshold calculated by probit analysis. Results: Mean MDTs [min arc: mean ± standard deviation (range)] were: (a) un-blurred: 5.5± 0.8 (4.9-6.1); 5.1±1.4 (3.8-6.7); 3.5±1.3 (2.6-4.4) (b) blurred DSph: 8.4±2.5 (5.1-14.8); 6.2±2.2(3.1-10.0); 5.9±2.5(1.7-10.9) for 43, 86 and 128 min arc line lengths respectively and (c) blurred DCyl: 5.6±2.1 (3.2-8.7); 6.5±2.4 (3.8-12.6) for 86 min arc line length, 90 and 180 degree axis respectively. Mean min arc change in threshold (blurred-un-blurred) showed a similar pattern for all line lengths: Blurring by +2.0DSph, +4.0DSph and all cylinders produced only small elevation in MDT (<2 min arc) for both subjects. Increase in MDT was found for +6.0DSph and -2.0DSph (<5 min arc) and -6.0DSph and -4.0DSph (< 9min arc). Conclusions: MDT testing is shown to be robust to the effects of blurring by DCyl. This is of particular interest in the development of the new test with respect to the use of an orientated line stimulus and consideration of peripheral astigmatism, which is reported to physiologically increase with eccentricity (Millodot 1981). The least MDT change is found when using a cylinder orientated at 90 degrees as optically predicted for a horizontal line stimulus. Wear of near spherical correction (with exception of subjects < -4.0DSph) will ensure optimum MDT sensitivity and specificity. Supported by an unrestricted grants from Pharmacia, The Friends of Moorfields and IGA
Keywords: motion-2D • refraction