The eye is an optical system similar to a camera. Light and images coming from outside are refracted in the cornea (the outermost transparent layer of the eye) and the lens layer and reach the vision point on the retina. In a normal eye, rays coming from outside are refracted in the cornea and lens and fall on the vision center, creating a clear image. In some cases, depending on the structure of the cornea, lens and eye, images may not be clearly formed on the retina.

MYOPIA
It develops as a result of the focusing of rays coming from outside before reaching the vision point. It occurs due to the long front-back axis of the eye or when the refractive power of the cornea and lens changes. Since the ability to adapt is very low in myopic eyes, the person has to use glasses to see far.

ASTIGMATISM
It occurs when the refractive power of the cornea is different in two perpendicular axes and the image is refracted in different planes. It may vary depending on the structure of the cornea and lens. Astigmatism causes reflection and blurred vision at every distance. Astigmatic vision can be likened to the image formed by the crooked mirrors in circuses.

HYPEROPIA
It develops as a result of the external rays focusing behind the visual point. It occurs due to the shortness of the front-back axis of the eye or in cases where the refractive power of the cornea and lens changes. The ability to adapt is high in hypermetropic eyes. Low-degree hypermetropic people can see normally by adapting, but the eye tires quickly. High hypermetropia, on the other hand, has both distant and near vision impairments.

PRESBYOPIA (AGE-RELATED NEAR VISION DISORDER)
It is the loss of flexibility of the lens due to advancing age and the resulting impairment of near vision. It starts at the age of 35-40 and progresses continuously until the age of 60.

KERATOCONUS
It is the thinning of a section on the corneal surface and its protrusion forward. These people cannot see clearly with glasses. Depending on the degree of the disease, they can use specially produced contact lenses. In very advanced cases, corneal transplant surgery called keratoplasty may be required.