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N. V. Rangaswamy, D. C. Hood, D. G. Birch, K. G. Locke; A Comparison of Visual Field Sensitivity to Photoreceptor Thickness in Retinitis Pigmentosa (RP). Invest. Ophthalmol. Vis. Sci. 2009;50(13):984.
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© ARVO (1962-2015); The Authors (2016-present)
To explore the relationship between visual field sensitivity and photoreceptor outer segment thickness in patients with retinitis pigmentosa (RP).
Static automated perimetric fields with Humphrey Field Analyzer and fourier-domain optical coherence tomography (fd-OCT) scans with Spectralis HRA+OCT were obtained from 10 patients with RP and 5 age-matched normal controls. The patients had a visual acuity of 20/32 or better, a visual field of at least the central 20 degrees, a foveal sensitivity of 30 dB or better, and no cystoid macular edema. Line scans (average of 100 frames) centered on the fovea along the horizontal meridian and volume scans (average of 12 frames per scan) in the nasal, temporal, superior and inferior quadrants were obtained with the fd-OCT. The distance between retinal pigment epithelium (RPE)/Bruch’s membrane (BM) to the photoreceptor inner-outer segment (IS/OS) junction (RPE-OS) was measured at points corresponding to the visual field testing points along the horizontal and vertical meridians. For each location, the loss in thickness, compared to the control value, was plotted against the loss in field sensitivity, also relative to the control value, for that location.
The average RPE-OS thickness in the control eyes was 63.1 + 5.2 µm varying from approximately 69 µm in the center to 56 µm at 20° eccentricity. In patients, RPE-OS thickness decreased with increased loss in local field sensitivity, reaching an asymptotic mean value of 20 µm at a loss of about 10 dB. When the visual sensitivity loss was converted to linear units, a 50% reduction in visual sensitivity corresponded to 67% reduction in photoreceptor thickness (slope = 0.5, intercept = 0.41, r2=0.53).
In patients with RP with good foveal sensitivity, local photoreceptor outer segment thickness decreases with loss of local field sensitivity. In general, in regions where perimetric sensitivity loss is reduced by 10 dB or greater, the thickness is reduced to only the RPE/BM complex.
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