**Question:** In complete albinism the colour of iris is:

A. Blue
B. Green
C. Hazel
D. Brown

**Core Concept:**
Albinism is a genetic disorder characterized by deficient or absent production of melanin, the pigment responsible for skin, hair, and eye color. Complete albinism results in complete absence of melanin, leading to a distinctive appearance.

**Why the Correct Answer is Right:**
In complete albinism, melanocytes (the cells responsible for melanin production) are absent or dysfunctional. This results in a complete lack of melanin in the skin, hair, and eyes. Since melanin provides color to the iris, the iris in individuals with complete albinism is devoid of pigment. Therefore, the correct answer is **D. Brown**, as brown eyes typically contain melanin in the iris.

**Why Each Wrong Option is Incorrect:**
A. Blue (option A) and Green (option B) options are incorrect because melanin is present in the iris, giving blue or green color. Blue eyes contain melanin in the anterior chamber, while green eyes have it in the posterior part of the iris.
C. Hazel (option C) is incorrect because it refers to a mix of brown and blue, which is not consistent with the absence of melanin in complete albinism.

**Why the Correct Answer is Right:**
Melanin is the pigment that gives color to the iris and is responsible for the various eye colors we see. In the case of complete albinism, there is a complete absence of melanin, leading to the iris being colorless and appearing white.

**Why Each Wrong Option is Incorrect:**
A. Blue (option A) and Green (option B) are incorrect because melanin is present in the iris, giving blue or green color. Blue eyes contain melanin in the anterior chamber, while green eyes have it in the posterior part of the iris.
C. Hazel (option C) is incorrect as it refers to a mix of brown and blue, which is not consistent with the absence of melanin in complete albinism. Hazel color results from the combination of brown and blue pigments, which do not exist in albinism.
D. Brown (option D) is the correct answer because it represents the absence of melanin in the iris, which leads to a colorless iris in individuals with complete albinism.

**Clinical Pearls:**
1. Complete albinism is a rare genetic disorder caused by mutations in genes responsible for melanin synthesis.
2. Albinism can be associated with other developmental abnormalities and ocular issues, such as photophobia, photoreceptor degeneration, and nystagmus.
3. Individuals with albinism usually have reduced vision due to the absence of melanin in the cornea, lens, and retina. This leads to a lack of light absorption and scattering, resulting in visual impairment.