Signs and Symptoms
Oculocutaneous as well as ocular albinos exhibit similar ocular and visual dysfunction. The oculocutaneous albino patient manifests reduced acuity, photophobia, strabismus, significant refractive error with astigmatism, transillumination of the iris and globe, nystagmus, blonde fundus with visible choroidal vasculature, and macular hypoplasia. A super-normal EOG and ERG is also present.
Transillumination of the iris and globe results from insufficient uveal pigmentation and poor development of the retinal pigment epithelium. This leads to a funduscopic picture of a blond fundus with extensive areas of hypopigmentation and clearly visible underlying choroidal vasculature. The pigment of the RPE acts as a sink for incoming light. When the RPE is underdeveloped, light scatters within the eye, producing the subjective complaint of photophobia.
The level of visual acuity varies among albino patients according to the amount of ocular pigmentation present and the concomitant level of macular development. Ocular albinos have variable amounts of uveal pigmentation and the potential to have the best acuity (20/25 to 20/300) among albinos. Oculocutaneous albinos exhibits less pigmentation than their ocular albino counterparts and tend to have lower acuity levels (20/80 to 20/400).
Systemically, albino patients may exhibit difficulties with healing and infection, as well as bleeding (Chédiak-Higashi syndrome and Hermansky-Pudlak respectively). Clinicians should ask questions in the history regarding bruising, nosebleeding and healing.
Tyrosinase-positive and -negative oculocutaneous albinos possess an autosomal recessive inheritance pattern. Oculocutaneous albinism results from incomplete melanization of the cellular melanosomes. In tyrosinase-negative oculocutaneous albinism, the congenital inactivity of the enzyme tyrosinase prevents the cells use of tyrosine in the formation of the pigment melanin. In tyrosinase-positive oculocutaneous albinism, tyrosinase activity is normal, but there is an inability of the cells to sequester the synthesized melanin into the melanosomes.
An autosomal recessive subtype of tyrosinase positive oculocutaneous albinism commonly seen in Puerto Rico is the Hermansky-Pudlak syndrome. Here, patients exhibit hemorrhagic diathesis (a tendency toward easy bruising and bleeding) due to a platelet dysfunction along with normal tyrosinase activity.
Another autosomal recessive subtype of oculocutaneous albinism is the Chédiak-Higashi syndrome. Here, patients may have a silvery sheen to their skin, and blue to brown irides. Normal tyrosinase activity within hair bulbs shows increased susceptibility to infection, hepatosplenomegaly, lymphadenopathy and a predisposition to development of a lymphoma-like condition.
Ocular albinism, in contrast to oculocutaneous albinism, exhibits pigmentary dilution due to abnormalities in melanosome synthesis rather than inadequate melanization. Ocular albinism is transmitted through either an X-linked or autosomal recessive mode. The hair and skin of the ocular albino tends to show a much greater pigmentation than that of the oculocutaneous albino, often falling into a normal pigmentation range. The uveal pigmentation of the ocular albino is variable and may range from very hypopigmented to a nearly normal pigmentation level.
Both ocular and oculocutaneous albinism exhibit a hypoplastic macula. Orderly retinal morphogenesis depends on the organizing influence of the adjacent retinal pigment epithelium. The insufficient uveal pigmentation and poor development of the RPE in the albinotic patient provides a developmentally unstable substrate for normal retinal organization. Hence, the albinotic macula is always hypoplastic and the albinotic patient has secondarily reduced acuity. This maldevelopment of the macula explains the pendular nystagmus of the albino patient, as the albino eye constantly searches for a clear image.
Strabismus is also often present in both ocular and oculocutaneous albinism. Research indicates that there is a disorganization of reticulogeniculate projections in the albino patient with 20 percent of temporal fibers decussating at the optic chiasm and projecting to the contralateral dorsal lateral geniculate nucleus rather than the ipsilateral nucleus.
Clinically, tyrosinase-positive oculocutaneous albinism exhibits the better prognosis as pigmentation may increase somewhat throughout life and visual disability is not as severe. The level of visual functioning of the ocular albino varies directly with the level of uveal pigmentation developed.
Genetic counseling should be suggested in appropriate cases. Laboratory testing for albino patients may include a complete blood count (CBC with differential), prothrombin time (PT), partial thromboplastin time (PTT), platelet aggregation testing, electroretinogram (ERG), electro-oculogram (EOG), tyrosinase testing and neuroradiologic studies (CT, MRI).
Other reports in this section
Eyelids & Eyelashes | Conjunctiva & Sclera | Cornea
Uvea | Vitreous & Retina | Optic Nerve & Brain | Oculosystemic Disease
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