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There are 4 names in this directory beginning with the letter P.
Posterior Chamber
The posterior chamber is a narrow chink behind the peripheral part of the iris of the human eye, and in front of the suspensory ligament of the lens and the ciliary processes. The posterior chamber consists of small space directly posterior of the iris but anterior to the lens.

Presbyopia is the eye's diminished ability to focus that occurs with age. A widely held theory arises from the loss of elasticity of the crystalline lens, although changes in the lens's curvature from continual growth and loss of power of the ciliary muscles have also been postulated as its cause.

Ptosis is drooping of the upper eyelid. The lid may droop only slightly or it may cover the pupil entirely. Uncorrected congenital ptosis can cause amblyopia also known as “lazy eye.” If left untreated, amblyopia can lead to permanently poor vision. Except in mild cases, the treatment for childhood ptosis is usually surgery to tighten the levator muscle that lifts the eyelid. Whether they have had surgery or not, children with ptosis should be examined annually by an ophthalmologist for amblyopia, refractive disorders, and associated conditions.

The pupil is the 'black circle' that you see in people's eyes. The primary function of the pupil is to control the amount of light entering the eye. When you are in a bright environment, the pupil becomes smaller to allow less light through. When it is dark, the pupil expands to allow more light to reach the back of the eye.