Dynamics of Visual Adaptation are Altered in Vascular Disease

Abstract

The eye has a relatively fixed contrast sensitivity over a large range of normal daytime light levels. However, sudden changes in the environmental light level require that the eye readjusts in order to achieve the same contrast sensitivity at the new level, a process which takes many seconds or minutes when the new environment is considerably dimmer than the previous level. During this recovery time, the eye is relatively blind to fine detail, its contrast sensitivity being reduced while it adapts. The initial stages of recovery are rapid and generally thought to involve neural processes in the retina [1], whereas the predominant slow phase is related to the rate of regeneration of the bleached photopigment. Any drug or disease that affects the photoreceptors, the pigment epithelium, or the adjacent choroid is expected to prolong the recovery of sensitivity because the recovery is dependent on regeneration of the photopigment, which is located in the outer segments of the receptors. In fact, certain drugs such as alcohol, even in low doses [2], and antimalarial drugs [3] have been shown to prolong recovery of sensitivity. It has also been demonstrated that ocular diseases such as senile macular degeneration, retinal pigment epithelial detachment, and central serous retinopathy significantly delay recovery even when visual acuity is normal or only marginally affected [4,5,6,7,8]. Processes that interfere with the active metabolism required to perform the regeneration of visual pigments such as decreased retinal vascular supply or from the choriocapillaries are also expected to prolong recovery.