FAQ

What are tears?

Tears are the liquid product of a process of lacrimation to clean and lubricate the eyes. The word lacrimation (also spelled lachrymation) may also be used in a medical or literary sense to refer to crying. Strong emotions, such as sorrow or elation, may lead to crying. The process of yawning may also result in lacrimation. Although most land mammals have a lacrimation system to keep their eyes moist, humans are the only mammal generally accepted to cry emotional tears.

Why do eyes have different colours?

The coulous of eyes is a polygenic trait and is determined by the amount and type of pigments in the eye's. Humans and animals have many phenotypic variations in eye color.In human eyes, these variations in color are attributed to varying ratios of eumelanin produced by melanocytes in the iris. 

There are three main elements within the iris that contribute to its colour:

1. the melanin content of the iris pigment epithelium
2. the melanin content within the iris stroma
3. the cellular density of the iris stroma.

Colour variations among different irises are typically attributed to the melanin content within the iris stroma. The density of cells within the stroma affects how much light is absorbed by the underlying pigment epithelium.The OCA2 gene polymorphism, close to proximal 5′ regulatory region, explains most human eye-color variation.

Why do red eyes appear in photos?

The red-eye effect in photography is the common appearance of red pupils in color photographs of eyes. It occurs when using a photographic flash very close to the camera lens, in ambient low light. Red-eye effect appears in the eyes of humans and animals that have no tapetum lucidum, hence no eyeshine, and rarely in animals that have a tapetum lucidum. The red-eye effect is a photographic effect, not seen in nature.

What is conjuctivitis?

Conjunctivitis is an inflammation of the conjunctiva (the outermost layer of the eye and the inner surface of the eyelids), most commonly due to an allergic reaction or an infection (usually bacterial, but sometimes viral).

What is the function of the eyelids?

An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes which serve to heighten the protection of the eye from dust and foreign debris. "Palpebral" (and "blepharo") means relating to the eyelids.