A role for photoreceptors in retinal oedema and angiogenesis: an additional explanation for laser treatment?

Abstract

Purpose To investigate the possible roles of retinal photoreceptors in macular oedema and retinal angiogenesis with particular reference to the mode of action of laser therapy. Methods (i) Studies in rats made hypoxic for 2 h by administering an oxygen/nitrogen mixture of reduced oxygen content, and growth factors determined by RT-PCR, western blotting, and immunohistochemistry. Assessment of blood-retinal barrier integrity using fluorescent and electron-dense tracers.(ii) Studies in pigs with one retina made hypoxic by selective embolisation of the retinal capillary circulation with fluorescent microspheres. (iii) Assessment of laser therapy in selected cases of retinal neovascularisation indicating a role for photoreceptors. Results In the hypoxic retina, angiogenic and vascular permeability factors such as vascular endothelial growth factor (VEGF), nitric oxide synthases (NOSs), and insulin-like growth factor-1 are upregulated in retinal astrocytes and Mü ller cells but are also present in large amount in the photoreceptors. Hypoxiainducible factor-1 (HIF-1) is upregulated in retinal glial cells but not in the photoreceptors, suggesting that growth factors in the photoreceptors may not have been generated there. The tracer dye, rhodium isothiocyanate, leaking from an abnormally permeable inner blood-retinal barrier in the hypoxic retina accumulates in the photoreceptors. Conclusions The results indicate that laser treatment of macular oedema or retinal neovascularisation may obtain its effect not only by improving oxygen availability in the inner retina, but also by reducing the load of angiogenic/permeability factors that accumulate in the photoreceptors in hypoxic/ ischaemic conditions.

Association between myopia and diabetic retinopathy: a review of observational findings and potential mechanisms

“…This speculation was further supported by evidence from later studies conducted by Sawada et al . In addition, it has been observed that pan‐laser photocoagulation destroys the outer retinal layer, leading to increased oxygen tension in the remaining retinal tissues and a decrease in vascular endothelial growth factor production, observed in animal models as well as in human . However, there has been no study to date to verify any of these theories in diabetic eyes.…”

Recent developments in laser treatment of diabetic retinopathy

“…It appears to be combined effects of multiple elements including: Facilitation of transports of oxygen and nutrients into the retina from choroid, transport of metabolic waste out of the retina, reduction of retinal metabolic load, and reduced sequestration of proangiogenic cytokines in the photoreceptors, resulting in net reduction of VEGF expression. 14 22 Other cytokines such as heat shock protein and transforming growth factor-β2 have been implicated in inflammatory response in retinal photocoagulation as well. 23 24 …”

Alternative approach to laser methods of treating vascular pathologies of the eye

“…However, classical panretinal photocoagulation (irradiation time by a "green" laser greater than 0.1 s), detectable by a visible clinical effect (greying or whitening of the retina, which corresponds to the photoreceptor-damage threshold) has significant side effects-CNV, paracentral scotomas (reduction of peripheral, color, and nighttime vision), and subfoveal reddening. It does not restore vision (the photoreceptors are not regenerated 21 ) but only prevents further loss of vision, with a high probability of recurrence of CNV.…”