Abstract
Purpose: :
Visual field sensitivity is a standard measure for following progression in patients with retinitis pigmentosa (RP). Previous studies have established the rate of progression in visual field area in patients with RP using kinetic perimetry (1-4). As well, Birch et al (5) examined five-year changes in static perimetric thresholds averaged across the visual field. There is, however, little information about the progression of visual field loss in different retinal areas in patients with RP. In the current study, we examined changes in Humphrey visual field (HVF) thresholds as a function of retinal eccentricity in a group of patients with RP.
Methods: :
HVFs for one eye of thirty-nine patients with RP were compared over follow-up periods ranging from two to twelve years (median number of visits = 4). At the initial examination, all patients had visual acuities better than 20/40. Full-threshold HVF testing was done using a modified program that tested 103 points (including the fovea) corresponding to our multifocal ERG array. In a few cases, visual field results from standard 30-2 or 10-2 full-threshold HVFs were included using a point-by-point comparison to line up the field values. The results for each patient were compared to those from 10 age-similar subjects with normal visual acuity and normal HVFs by subtracting the patient threshold values from the averaged value of the control group.
Results: :
The results were analyzed separately for the fovea, ring 1 (out to 5o), ring 2 (out to 10o) and the periphery (all remaining points to 25o). The data were transformed into linear units for averaging. For each eccentricity, the median loss in sensitivity for the patients was plotted as a function of years of follow-up and regression lines for the data were calculated. The median HVF loss at the initial visit varied with eccentricity; from 3.3 dB loss at the fovea to 13.8 dB loss for the periphery. In addition, the amount of progression (slope of the regression line) increased with eccentricity, from 0.07 dB loss/year for the fovea to 0.94 dB loss/year for the periphery. There were no significant differences between the slopes for the fovea, 5 o or 10 o (p > 0.05) but the slope for the peripheral data was significantly steeper than were the other slopes (p <0.05).
Conclusions: :
We found eccentricity-dependent rates of field progression in patients with RP. These results have implications for current studies involving therapeutic interventions.References: 1. Massof, et al, 1990; 2.Berson, et al, 1985; 3. Holopigian, et al, 1996; 4. Grover, et al, 1997; 5. Birch, et al, 1999.
Keywords: retinal degenerations: hereditary • visual fields • perimetry