eye diseases/refractioonimpairments

Eye is an optical system resembling camera. Light and images coming from outside reaches to visual cortex refracting by cornea (transport layer located on topcoat) and lens layer. In a normal eye, beams from outside forms net images drops on to visual cortex after refracting in cornea and lens. In some cases images may not be formed net on retina due to structure of cornea, lens and eye.

MYOPIA 

It develops as a result of focusing light beams before reaching visual cortex. It appears in the cases the length of front-back axis of eye is more than required or refractivity of cornea or lens changes. Adjustment capability of short sighted eyes is very low, the person has to use glasses to see longsighted.

ASTIGMATISM

It appears since image is refracted in different planes due to difference of refractive index for two axis vertical to each other. It may change due to the structure of cornea and lens. Astigmatism causes reflection and blurred vision for every distance. Astigmatic vision is similar to that vision formed in the distorting mirrors in circus. 

HYPERMETROPIA

It develops as a result of focusing light beams after visual cortex. It appears in the cases the length of front-back axis of eye is shorter than required or refractivity of cornea or lens changes. Adjustment capability of hypermetropic eyes is higher. Persons having low degree hypermetropia may see normal with self adjustment but their eyes gets tired too fast. People having high hypermetropia have short and long distance visual impairment. 

Presbiophia (Age dependent short distance visual impairment)

Short distance visual impairment which is caused by loss of flexibility of lens due to increasing age. This kind of visual disorder starts by the age 35-40 and progresses until the age 60.