What is Cataract | Definition of Cataract
What is Cataract ? Lens opacity is a simple definition of cataract. Cataract is an opacity or cloudiness of the natural lens inside the eye. It is very common in old age. It is consider as a natural aging process but the amount of lens opacity will change from person to another and will be determined by many factors which will be discussed later.
It is usually bilaterally or in both eyes but sometimes due to certain factors like trauma it can be in one eye only. It is not contagious to the other eye or to other people in close contact and once it is removed completely, it will not come back again.
Cataracts start very mild and progress slowly and the time of this progression is different from one person to another and even is different between both eyes in the same person. There are various types of cataracts. In traumatic cataracts, the progression will be fast in which it can be mature within days or even hours. While in age related cataract, it can progress through years.
What is the lens?
Inside human eye and behind the iris (the colored part of the eye), there is a natural clear transparent lens which can change its shape and thickness to help the light rays to focus on the vision center in the retina which is called fovea.
This lens is made from water and proteins which is called crystalline proteins. They are arranged in special manner so that the lens will be clear. The lens material lies inside a bag called capsule.
The lens has layers like onion in which the inner most layers called nucleus while the outer most layer called cortex
In order the light rays to reach this vision center, all the passing media including the lens should be clear. Once lens opacity or cloudiness in the lens occur, less light will pass to the retina and so vision will be blurred and not clear.
Types of Cataract
Understanding what is cataract is essential. Types of cataract will depend on which part of the lens has the opacity.
1- Nuclear cataract or nuclear sclerosis
It is the most common type of cataract that occurs in age-related cataract and in patients with diabetic mellitus. It occur in the center of the lens.
2- Cortical Cataract
which is the second most common cataract and from its name it occurs in the cortex or the outer part of the lens.
3- Posterior Subcapsular Cataract
Which occur in the posterior part of the lens and it occur mostly with corticosteroid and it can occur also in diabetic patient.