Laboratory Studies
Oculocutaneous albinism and ocular albinism are primarily clinical diagnoses.
The tyrosinase hair bulb incubation test is a simple test that can differentiate between tyrosinase-negative and tyrosinase-positive forms of albinism. Hair bulbs from a patient with albinism are incubated with tyrosine in a test tube. Hair bulbs from tyrosinase-positive patients demonstrate some degree of pigment production, while those from tyrosinase-negative patients have no pigment production. Since most of the albino phenotypes are tyrosinase positive, this test provides limited information in determining the exact type of albinism.
Simple blood clotting tests can be performed if Hermansky-Pudlak syndrome is suspected. The clotting parameters are reduced in patients with this disease because of defective platelets.
Imaging Studies
The visual-evoked potential (VEP) may be used to help confirm the diagnosis of albinism. Patients with albinism show an asymmetry of VEP between the 2 eyes secondary to misrouting of the optic pathways. This makes VEP a very accurate diagnostic test for albinism.
In a study of 13 patients, Seo and colleagues used optical coherence tomography (OCT) to develop a grading system based on foveal hyporeflectivity, the degree of choroidal transillumination, the presence of a tram-tract sign, and foveal depression. [10] They found that these measurements correlated with the visual prognosis. [10]
Macular OCT can be helpful in making a diagnosis of atypical cases of oculocutaneous albinism as reported by Rossi et al. [11] According to authors, OCT showed high reflectivity across the fovea without foveal depression in an atypical case of oculocutaneous albinism and helped in making the correct diagnosis. These OCT findings are a typical pattern for oculocutaneous albinism. [12]
In a study by Sepúlveda-Vázquez et al, spectral-domain optical coherence tomography (SD-OCT) showed development of inner retinal layers in the fovea, abnormality of the Henle layer, and lack of thickening in the perifoveal area. [13]
Anterior segment OCT can also be used to detect iris abnormalities associated with albinism and can help in making the diagnosis and evaluating the intensity of albinism, as reported by Sheth et al. [14]
A concentric macular ring sign can be seen via infrared reflectance, as reported by Cornish et al. [15]
Prins et al noted that MRI can help in determining the structural changes in brain and visual pathways and can also help as a diagnostic tool and in development of future treatment modalities. [16]
Mohammad et al reported on the morphologic abnormalities of the optic nerve head in patients with albinism using scleral domain OCT. They found that patients with albinism have significantly smaller cup-to-disc ratios and that their peripapillary retinal nerve fiber layer was significantly thinner than that in the control group. [17]
Other Tests
Light microscopy of the blood smear can be performed in patients suspected of having Chediak-Higashi syndrome. The blood smear from these patients shows neutrophils with large inclusions.
Even though not routinely performed, electron microscopic study of the skin or the hair bulbs is probably the best diagnostic method for albinism.
Even though still not widely available, gene sequence analysis can be performed to differentiate between various forms of albinism.
Procedures
A skin biopsy can be performed to make the diagnosis of albinism in cases that are not clinically obvious. Skin biopsy also is helpful to determine the female carrier state in cases of X-linked ocular albinism.
Histologic Findings
Histologic evaluation of the skin, hair, and eyes from patients with oculocutaneous albinism reveals a generalized absence of melanin pigment. There is also an absence of foveal differentiation and generalized deficiency of retinal pigment. Lipidlike deposits can be present in ciliary and iris epithelia. In addition, abnormal melanin macroglobules are present in melanocytes. These macroglobules are present not only in the iris, ciliary epithelium, and retinal pigment epithelium but also in dermal melanocytes. These macroglobules are also present in the skin biopsy of carrier females of X-linked ocular albinism. (It should be emphasized here that, even though the subdivision of albinism into oculocutaneous and ocular forms is helpful to the clinician, it is not entirely accurate histopathologically. All forms of ocular albinism involve, to a small degree, cutaneous pigment abnormalities.) Patients with Hermansky-Pudlak syndrome have a ceroidlike material present in their tissues.
