Times have changed. When I started my first practice in 1987, I quickly explained how the eye worked by using the analogy of a camera. The front surface of the lens acted the same as the cornea. The diaphragm functioned similarly to the iris and pupil. The retina acted like the camera’s film.
I used this analogy with a younger patient last week when it dawned on me that they had no idea what I meant. Growing up in the digital age, many younger patients have never loaded film in the back of a camera or experienced the joy of waiting two weeks to see if any of their photos turned out. So, in this newsletter, I will go over some basic eye anatomy for your future reference.
Above are two eye diagrams, a front view and a side view
The conjunctiva is a very thin transparent membrane covering the sclera. Any inflammation or infection of the conjunctiva is called conjunctivitis.
The sclera is the hard outer shell of the eye that provides its strength and support.
The cornea is a clear dome on the front of the eye. If you touch the front of the eye, you touch the cornea. The cornea has an abundance of nerve endings, as anyone who has had a corneal abrasion knows.
Located between the cornea and iris/pupil is a space filled with liquid known as the aqueous humor.
Iris and Pupil
The iris is the colored part of the eye. The pupil is the hole in the iris. The iris is partly responsible for regulating the amount of light permitted to enter the eye. The muscles in the iris can make the pupil larger or smaller.
Lens, Zonules, and Ciliary Body
The lens is a clear structure that focuses light on the retina. The lens is attached to the ciliary body by fibers known as zonules. Relaxing and contracting the ciliary body changes the shape of the lens, allowing us to focus from distance to near. A cloudy lens is called a cataract.
The center, hollow structure of the eye is filled with vitreous. The vitreous has a consistency similar to raw egg whites. It is clear and allows light to pass through.
Sandwiched between the sclera and the retina is a layer known as the choroid. This layer is rich in blood vessels and supplies most of the nutrients to the eye. When you look inside the eye, the red color is coming from the choroid, visible through the transparent retina.
The retina consists of millions of photoreceptor cells. These are nerve endings that can detect light. These photoreceptors consist of cones (color vision) and rods (black and white vision).
Macula and Fovea
The posterior retina is called the macula. Within the very center of the macula is a small spot known as the fovea. When you look directly at an object, the image focuses on the fovea. Damage to this area is called macular degeneration.
Optic Nerve and Optic Disc
The nerve fibers from the retinal photoreceptor cells gather together to exit out of the back of the eye to form the optic nerve. The end-on view of the optic nerve exiting the eye is called the optic disc. The optic disc is the primary area of damage caused by glaucoma.
The above diagram shows a cross-section of the upper eyelid. Notice the Meibomian glands located behind the eyelashes. These glands help with tear production.
I hope this has been helpful in providing a better understanding of eye anatomy.
This newsletter does not constitute medical advice. Make sure to contact your healthcare provider if you experience any of these conditions. Do not make any changes to your medications before consulting your physician.