Photostress test
Photostress recovery time (PSRT) is the time taken for visual acuity to return to normal levels after the retina has been bleached by a bright light source. Photostress recovery time measurement procedure is known as photostress test. Normal recovery time is about 15–30 seconds. The photostress test is a simple, easy and quick clinical technique that can differentiate between retinal (macular) and postretinal (e.g.optic nerve) disease. Clinical significance. The photo stress test is clinically useful in diabetes, glaucoma, macular degeneration etc. Diabetic retinopathy affects the microvasculature of the inner retina and causes neurodegeneration. Several studies reported that PSRT  is elevated in people with diabetes. Recovery time is more in macular diseases (50 seconds or more) than postretinal (e.g.optic nerve) diseases. Elevated PSRT has also been found in primary open angle glaucoma (POAG) which is characterized by progressive death of the retinal ganglion cells. Amblyopic eyes with normal fundus also have normal recovery time. Materials needed. Ophthalmoscope or alternative source of light (e.g.penlight), stop watch, distance vision charts like a Snellen chart. Disadvantages. The main disadvantage of the test is that there is no standardization of the procedure. The effect of aging on recovery time is also thought as  a disadvantage, but it is still under discussion since some studies found increased PSRT with age, and others did not find any significant effect.