University:
Eastern Kentucky University
Course:
BIO 273 | Clinical Microbiology
Academic year:

2022
Views:

141

Pages:

4
Author:

esfredint7qo

Basics of Ophthalmology for Dental Students Background • The eye is the organ of sight. • It is designed to allow light rays to stimulate the retina where is converted into electric impulses using specialized nerve ending and it is conveyed to the brain via the optic nerve. • It is protected within the bony orbit and it is surrounded by orbital pad of fat. • It can freely move in all directions by extraocular muscles. Anatomy of the eyeball • The eyeball is about 24 mm in diameter. It has 3 coats: 1. Outer protective coat: Cornea and sclera. 2. Middle vascular and pigmented coat: Uveal tract (Iris, ciliary body and choroid) 3. Inner receptive coat: Retina. 1. Outer coat of the eyeball Cornea: • Anterior 1/6 of the outer coat. • Transparent and avascular. • 11 mm in diameter, 0.5 mm in thickness. • It admits light into the eye and it is the main refractive surface of the eye. Sclera • Posterior 5/6 of the outer coat. • White opaque tough coat of the eyeball. • 1 mm in thickness. • Posteriorly, it is pierced by the optic nerve. 2. Middle layer of the eyeball • It is the vascular, pigmented and nutritive layer. • It is called the uveal tract and it is divided anatomically into: Iris, ciliary body and choroid. Iris: • Formed the colored part of the eye. • It is a diaphragm with a central opening called the pupil which controls the amount of light entering the eye. • Its root is attached to the ciliary body. • It contains 2 types of plain muscles; sphincter pupillae supplied by the parasympathetic system and dilator pupillae supplied by sympathetic system. Ciliary body: • It is the part between the iris and the choroid. • It has an anterior part with ciliary processes to be attached the lens and posterior plane part. • Functions: 1. Secretes aqueous humor to control the intraocular pressure. 2. Contains the ciliary muscles responsible for accommodation to allow seeing near objects. Choroid: • It extends backwards from the ciliary body. • It is highly vascular and responsible for nutrition of adjacent structures. • It is highly pigmented. 3. Inner layer of the eyeball Retina: • It contains 3 layers of cells and responsible for converting the light rays into electric impulses. • 2 types of light receptors: 1. Cones: responsible for day vision and color vision. 2. Rods: responsible for night vision.  Structure of the retina: • Macula lutea: most posterior part, rich in cones and responsible for acute sharp vision, reading and differentiating colors. • Optic disc: is the point where the optic nerve leaves the eye and it is insensitive to light “blind spot”. • Peripheral retina: rich in rods and responsible for night vision.