Visual acuity was examined with a Snellen visual chart with a calibrated luminance. Then according to the equation that Snellen VA equals to 1/MAR (MAR= minimal angle of resolution), Snellen VA was converted into logMAR for statistics. For calculation, visual acuity of hand motion was converted into 20/2000 and light perception was converted into 20/20000 of Snellen fraction. Visula field examination was evaluated using Goldmann kinetic perimetry with varying sizes and illuminations of testing light spots. Then the degree of the widest visual field isopter was recorded. EOG: is used to assess function of retinal pigment epithelium. During dark adaptation, resting potential decreases slightly and reaches a minimum ("dark trough"). When the light is on, the resting potential increases ("light peak"). The ratio of light peak voltage versus dark trough voltage is known as the Arden ratio. The EOG was performed with pupil dilated, first in the dark for 15 minutes, and then in the light for 15 minutes and the Arden ratio for analysis was recorded.