Biology Quiz on Eye Anatomy and Cell Functions

Study Notes

Eye Histology

The eye has three concentric layers: sclera, choroid, and retina.
The eye has three chambers: anterior, posterior, and vitreous.
The cornea is a transparent structure.
The cornea lacks blood vessels.
Nutrients reach corneal cells through diffusion from tear fluid and aqueous humor.
The cornea has five layers: epithelium (stratified, squamous, non-keratinized, five or six layers, with microvilli on surface cells, rich with sensory nerve endings), Bowman's membrane, stroma (parallel collagen bundles, flattened fibroblasts, immersed in glycoprotein, contains some migrating lymphocytes, 5-10 mm thick), Descemet's membrane (homogeneous, fine collagenous filaments), and endothelium (simple squamous).
The corneal stroma features parallel collagen fibers, fibroblasts, and lymphocytes.
Corneal transparency is due to the absence of blood vessels, thin parallel collagen fibrils in the stroma, and the arrangement of corneal epithelium. Low water content also contributes.
The choroid layer is highly vascularized and contains fibroblasts, macrophages, and melanocytes.
The choroid has a choriocapillary layer (dense capillary network) and Bruch's membrane next to the retina.
The ciliary body and ciliary processes are involved in lens accommodation, a process that regulates lens thickness.
The ciliary body features pigmented and non-pigmented ciliary epithelial cells.
The iris contains smooth muscles (sphincter and dilator pupillae) controlling pupil size. The number of melanocytes is roughly similar in all people, but the amount of melanin pigment in each melanocyte determines eye color. This variation is due to genetic differences in melanocyte protein expression, such as tyrosinase and melanocortin receptor.
The pigmented epithelium behind the iris reflects light.
The lens is transparent.
The lens separates the aqueous humor anteriorly and vitreous humor posteriorly.
The lens is composed of capsule, subcapsular epithelium, lens cortex (fibers), and crystalline core proteins.
Cataracts are common lens abnormalities where the lens loses transparency. Cataracts are caused by degeneration of crystalline proteins.

Clinical Applications

Corneal avascularity makes corneal surgery more successful, with a high success rate.
Corneal transplant rejection is rare due to lack of blood vessels.
LASIK (laser-assisted in situ keratomileusis) is a laser procedure used to reshape the cornea to improve vision in patients with corneal abnormalities.
Corneal endothelium pumps water into the aqueous humor to keep the corneal stroma relatively dehydrated.