Operating in the Dark: A Night-Vision System for Surgery in Retinas Susceptible to Light Damage
A standard operating microscope was modified with a bandpass infrared filter in the light path and infrared image intensifiers for each of the 2 eyepieces. We evaluated this system for subretinal injections in normal control dogs and those with a mutation in the rhodopsin gene. Rhodopsin-mutant dogs are a model for human autosomal dominant retinitis pigmentosa, and their retinas degenerate faster when exposed to modest light levels as used in routine clinical examinations. We showed that the mutant retinas developed severe generalized degeneration when exposed to the standard operating microscope light but not the infrared light. The modified operating microscope provided an excellent view of the ocular fundus under infrared illumination and allowed us to perform subretinal injections in the retinas of the rhodopsin-mutant dogs without any subsequent light-induced retinal degeneration. The first description of light-induced retinal damage showed that exposure of albino rats to visible light intensities ordinarily encountered in the laboratory led to irreversible retinal damage.1 This finding soon was extended to other species, including rabbits2 and monkeys.3 Studies in animal models of retinal degeneration (eg, Royal College of Surgeons rats, ABCA4-mutant mice, or rhodopsin-mutant mice and dogs) have emphasized the interplay between the gene mutation and environmental light and demonstrated acceleration of the disease process by light.4- 10 The effect of environmental light on disease severity in humans with retinitis pigmentosa has been suggested by case reports,11 although definitive proof is lacking. However, patients with class B1 rhodopsin mutations may be at risk of accelerated vision loss with increased light exposures because they have defects in dark (bleaching) adaptation similar to those found in rhodopsin-mutant dogs that demonstrate a high susceptibility to retinal light damage.8,12,13 Many of the emerging therapies for retinal degeneration require the intraocular placement of a reagent or device with the use of an operating microscope.14,15 The damaging effect of the microscope light on the normal retina, even with the appropriate filtering of UV light, has been described previously,16,17 and there is increased emphasis on reducing the intensity and duration of the exposures. Herein, we describe a modification of an operating microscope with an infrared bandpass filter and a night-vision system to perform surgical interventions in the posterior segment of the eyes of rhodopsin-mutant dogs without the risk of photochemical retinal damage. This modification prevents acceleration of the photoreceptor degeneration that occurs with exposure to modest light levels as used in routine clinical practice.8 If humans with retinitis pigmentosa are shown to have similar light damage susceptibility, this microscope modification could be considered for surgical procedures such as the subretinal application of gene therapy vectors.