Abstract
Purpose: :
Retinitis pigmentosa is characterized by degeneration of photoreceptors and the retinal pigmentation epithelium. The demand for oxygen in the outer retina can thus be expected to decrease. Oxygen is supplied to the outer retina from the choroid. Decreased function in the outer retina is likely to influence the function and metabolism in the inner retina. The decreased demand for oxygen in the outer retina will also allow oxygen from the choroid to diffuse freely to the inner retina.However, it is not known if these changes in oxygen demand are in fact reflected by the oxygen saturation in the inner retinal vessels. Therefore, we assessed the effects of the degeneration in retinitis pigmentosa on inner retinal oxygen metabolism.
Methods: :
The retinal oximeter (Oxymap ehf., Reykjavik, Iceland) is based on a fundus camera. It captures two fundus images simultaneously, at 570 and 600nm. The ratio of light absorbance at the two wavelengths is approximately linearly related to oxygen saturation. Retinal vessel oxygen saturation and vessel diameter were measured in six patients with retinitis pigmentosa (mean age 48 years, range 23-71 years) and compared to age and gender matched healthy individuals. All patients had advanced stage of the disease with visual fields restricted to the macular region. The saturation values were corrected for confounding effects of different vessel diameters.
Conclusions: :
Retinal arterioles and venules were narrower in patients with retinitis pigmentosa than in healthy individuals. No significant difference was found in oxygen saturation in this small sample. Unchanged (or decreased) arteriovenous difference in oxygen saturation combined with decreased vessel diameter indicate less oxygen delivery from the retinal circulation in retinitis pigmentosa. The results are consistent with increased diffusion of oxygen from the choroid to the inner retina and decreased inner retinal function.
Keywords: retinitis • oxygen • imaging/image analysis: clinical