Hemeralopia (Greek for "sun blindness") is the inability to see clearly in bright light and is the exact opposite of nyctalopia (night blindness). In hemeralopia, daytime vision gets worse and worse. Nighttime vision remains unchanged due to the use of rods as opposed to cones (during the day), which get affected by hemeralopia and in turn degrade the daytime optical response.
Hemeralopia is known to occur in several ocular conditions. Cataracts are the main cause of decreased vision due to clouding of the lens. The lens clouding disperses the light before it can reach the retina.
Another known cause is a rare genetic condition called Cohen Syndrome (aka Pepper Syndrome). Cohen syndrome is mostly characterized by obesity, mental retardation, and craniofacial dysmorphism due to genetic mutation at locus 8q22-23. Rarely it may have ocular complications such as hemeralopia, pigmentary chorioretinitis, optic atrophy or retinal / iris coloboma.Having a serious effect on the persons vision.