Phytanic acid is found in meat, fish, and dairy products. The body also converts phytol, a substance found in green leafy vegetables, to phytanic acid. Refsum disease is usually diagnosed during childhood or young adulthood when vision problems due to RP become apparent. Progressive vision loss from RP begins when harmful levels of phytanic acid collect beneath the retina. The retina is essential to vision as it converts light into electrical impulses and then transfers these impulses to the brain via the optic nerve.
Night blindness makes vision difficult in dark or dimly lit places.
The loss of peripheral vision is often referred to as tunnel vision. RP tends to progress slowly in patients with Refsum disease. Cataracts, which are common to RP, are also seen in individuals with Refsum disease. Cataracts hamper vision by clouding the lens of the eye making it difficult for light to reach the retina. In most cases, however, cataracts can be surgically removed.