From the Guidelines
The eye is a complex and highly specialized organ, and its detailed anatomy includes the cornea, conjunctiva, sclera, lens, retina, and optic nerve.
Key Components of the Eye
- The cornea is the transparent outer layer of the eye, composed of a highly regular, stratified squamous nonkeratinized epithelium, a transparent structural framework of precisely organized collagen fibrils, and a sodium-transporting endothelium 1.
- The conjunctiva is a translucent mucous membrane that covers the white part of the eye and the inside of the eyelids, comprising conjunctival epithelial cells and underlying vascular stroma 1.
- The sclera is the white, tough, outer layer of the eye, providing protection and structure.
- The lens is a clear, flexible structure behind the iris that changes shape to focus light on the retina.
- The retina is the innermost layer of the eye, containing specialized light-sensitive cells called photoreceptors (rods and cones) that convert light into electrical signals.
- The optic nerve is the nerve that carries these electrical signals from the retina to the brain, where they are interpreted as visual information.
Additional Details
The cornea is coated by a complex tear film structure composed of an aqueous nutrient-rich layer, and its thickness can vary between species, with human corneas having a mean central thickness of 536 mm, while porcine corneas are thicker, ranging from 659-995 mm 1. A comprehensive eye examination should include an evaluation of the physiological function and anatomical status of the eye, including visual acuity, refraction, visual fields, external examination, pupillary function, ocular alignment and motility, slit-lamp biomicroscopic examination, intraocular pressure measurement, and fundus examination 1.
From the Research
Overview of the Eye Anatomy
The eye is a complex organ, and understanding its anatomy is essential for appreciating the pathophysiology of ocular disease 2. The eye is composed of various membranes and fluids, including the cornea, sclera, choroid, capsula of the lens, and retina 3.
Membranes of the Eye
The membranes of the eye include:
- Cornea: the transparent outer layer of the eye
- Sclera: the white part of the eye
- Choroid: a layer of blood vessels between the sclera and retina
- Capsula of the lens: a transparent membrane surrounding the lens
- Retina: the innermost layer of the eye, responsible for detecting light and transmitting visual signals to the brain
- Bulbar conjunctiva and Tenon's capsula: membranes that cover the muscles of the eye and join the individual elements of the eye with the orbital cavity and skull 3
Fluids of the Eye
The fluids of the eye include:
- Egg-shaped fluid (albuminous fluid)
- Crystal fluid (the lens)
- Vitreous fluid 3
Surrounding Tissues
A working knowledge of the functional anatomy of the eye and its surrounding tissues is essential for performing a thorough physical examination of the eye 4. The surrounding tissues include the eyelid and the lacrimal system 5.
Evolution of the Eye
The evolution of the eye is a complex and debated topic, with some studies suggesting that animal eyes evolved multiple times independently, while others propose that they evolved from a common, simple precursor, the proto-eye 6. The molecular conservation of the pax6 eye-specifying cascade supports the latter theory 6.
Cell Types in the Eye
The eye contains various cell types, including photoreceptor cells, pigment cells, and lens cells, each requiring distinct combinations of specifying transcription factors to control their differentiation programmes 6. The evolution of these cell types can be reconstructed by comparing their molecular combinatorial codes 6.