Albinism
 

Iris transillumination in albinism A patient with oculocutaneous albinism with white eyebrows and lashes.

.  The patient may have oculocutaneous albinism or ocular albinism. The former should be easy to detect because the patient  has blond hair and white eyebrows and lashes. In the examination, the request may be examination of the anterior segment  or ocular motility (convergent strabismus and nystagmus are common in albinism). The patient has blond hair and poliosis. There may be obvious nystagmus (usually pendular) and convergent strabismus.  The iris shows transillumination. Other examination: Fundal examination may reveal macular hypoplasia (shown by absent foveal reflex and failure of the retinal vasculature to wreathe the fovea). The retina is hypopigmented making the choroidal vasculature easily visible. .

Questions:

1. How is albinism inherited?

Answer
The two most common forms of inheritance are X-linked recessive and autosomal recessive. Ocular albinism is usually X-linked recessive (also known as Nettleship-Falls type) whereas oculocutaneous form is commonly autosomal recessive.

2. Can one predict the severity of visual impairment in a child with oculocutaneous albinism?

Answer
Patients who can produce pigmentation have a less severe visual impairment than those who cannot produce any pigmentation. This can be determined using the hair bulb test (in patients over the age of 4). In this test, the hair bulb is incubated in a solution containing tyrosine. In patients who are tyrosinase-positive, pigmentation of the hair occurs which is absent in patients who are tyrosinase-negative.

3. How can visual evoked potential be used to diagnose albinism?

Answer
In albinism there is complete decussation of the visual pathway and therefore monocular stimulation of the retina will only give cortical signal on the contralateral cortex.

4. Do patients with albinism have normal life expectancy?

Answer
Life expectancy is usually normal. But some forms of albinism are associated with life threatening conditions. The two best known are:
Chédiak-Higashi's syndrome (easy susceptibility to recurrent infection due to abnormal immunity)
Hermansky-Pudlak's syndrome (easy susceptibility to bruising and bleeding)

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Left fundus of a patient with albinism. Note the lack of  RPE pigment which allows the choroidal vessels to become clearly visible. The patient also has macula hypoplasia, the temporal arcade of the retinal vessels run almost  horizontally. Return to the top