Abstract
Purpose::
To review factors, including dark adaptation, that may contribute to retinal hypoxia in retinal and choroidal vascular disease, and to discuss the potential effect of these phenomena on ROP, Diabetes Mellitus and Choroidal Neovascularization.
Methods::
Literature review and a 15 year retrospective review of the use of light adaptation in prethreshold retinopathy of prematurity in a tertiary care NICU.
Results::
The retina has a dual blood supply. Disturbance of either the retinal vascular or choriocapillaris component can potentially induce neovascularization due to excess VEGF production, resulting from retinal hypoxia. It is well established in animal models that under scotopic conditions the rod photoreceptors consume more oxygen due to increased dark current activity. This can develop within 100 seconds after turning lights off and is aborted within 100 seconds of turning lights back on (Cringle, Yu, Yu, Su. Invest Ophth Vis Sci 2002;43:1922-1927) . Avoidance of dark adaptation has been used by us for 15 years for adjunctive treatment of prethreshold ROP and has now been recommended in two papers for reducing the risk of developing diabetic retinopathy (Arden GB. BJO 2001;85:366-370 and Drasdo et al. Lancet, 2002;359:2251-2253). Two other studies show that choroidal blood flow in the macula is reduced under scotopic conditions, possibly due to a diversionary steal toward the rod dominant peripheral retina: (F. Miura et al, ARVO 2001, abstract #465) (H. Kergoat et al, ARVO 2002, abstract #3300). It may be theoretically possible that low level lighting (a nightlight) during sleep might reduce retinal hypoxia, thereby lowering the risk of retinal or choroidal neovascularization. Supporting evidence will be presented.
Conclusions::
Dark adaptation leads to increased rod photoreceptor oxygen consumption. This, in pathologic states such as ROP and diabetes mellitus, might increase retinal hypoxia, which in turn may lead to retinal neovascularization. In ARMD, choroidal blood flow may be diverted from the macula toward the periphery during dark adaptation, which theoretically might increase the local angiogenic stimulus for choroidal neovascularization in the macula. Low level lighting may provide a safe and inexpensive method for reducing these risks.
Keywords: age-related macular degeneration • diabetic retinopathy • retinopathy of prematurity