Albinism is a group of conditions that involve the synthesis of melanin in the skin and eye (oculocutaneous albinism [OCA]) or the eye alone (ocular albinism [OA]).
The major ophthalmic findings in all types of OCA and OA are iris transillumination from decreased pigmentation, foveal aplasia or hypoplasia, and a characteristic deficit of pigment in the retina, especially peripheral to the posterior pole (Fig 28-24A, B). Nystagmus, photophobia, high refractive errors, and reduced central visual acuity are often present, and visual acuity ranges from 20/25 to 20/200. If a child has significant foveal hypoplasia, nystagmus will begin at 2–3 months of age. The severity of the visual impairment tends to be proportional to the degree of nystagmus and foveal hypoplasia. Optical coherence tomography has demonstrated that the size of the photoreceptor outer segment is the trongest predictor of visual acuity. An abnormally large number of crossed fibers appear in the optic chiasm of patients and animals with albinism, precluding stereopsis and often inducing strabismus. Asymmetric visual evoked potentials are often seen in affected patients and may be helpful in diagnosis.
A, Transillumination of iris in albinism, right eye. B, Fundus in albinism, right eye, demonstrating complete lack of pigment and macular hypoplasia. C, Child with oculocutaneous albinism type 2. Note the white hair, eyebrows, and lashes and light-colored irides and freckles.
(Parts A and C courtesy of Edward L. Raab, MD.)
There are 4 major types of OCA, all of which exhibit various degrees of skin and hair pigmentation (Fig 28-24C). They are autosomal recessive and are caused by different gene mutations (Table 28-10).
Ocular albinism (OA1), also called Nettleship-Falls ocular albinism, is usually caused by a mutation in the GPR143 gene on the X chromosome. This gene controls melanosome number and size; the mutation results in macromelanosomes, which may be revealed by skin biopsy. Affected individuals appear to have decreased pigment in the eyes but not the skin. Patches of decreased pigment in the fundus and iris transillumination are apparent in many female carriers.
Albinism can be part of a broader syndrome, such as Hermansky-Pudlak syndrome or Chédiak-Higashi syndrome, both of which are autosomal recessive. Hermansky-Pudlak syndrome occurs with higher frequency in Puerto Rico and consanguineous populations and is characterized by pulmonary interstitial fibrosis and bleeding abnormalities. Chédiak-Higashi syndrome is a rare condition characterized by increased susceptibility to bacterial infections. Whenever albinism is diagnosed in a child, the clinician should inquire whether the patient has bleeding or bruising tendencies or experiences frequent infections.
Table 28-10 Classification of Major Types of Oculocutaneous Albinism (OCA)
Khan AO, Tamimi M, Lenzner S, Bolz HJ. Hermansky-Pudlak syndrome genes are frequently mutated in patients with albinism from the Arabian Peninsula. Clin Genet. 2016;90(1):96–98.
Mohammad S, Gottlob I, Kumar A, et al. The functional significance of foveal abnormalities in albinism measured using spectral-domain optical coherence tomography. Ophthalmology. 2011;118(8):1645–1652.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.