What Does an Eye Doctor See in a Patient’s Eyes?
By Michael J. Dodd, MD
Many patients ask me what I can see when I examine their eyes. I will try here to outline briefly in lay terms what we see during an eye exam and describe what we are looking for.
Perhaps the most important part of the eye exam is to determine the patient’s visual acuity. This documents the capacity to see “normally.” If a patient does not achieve 20/20 visual acuity, it is the eye doctor’s job to determine why and what can be done about it.
We first examine the area of skin around the eyes to look for any tissue lesions or growths; we look for droopy eyelids and check the pupils and determine that they react (constrict) normally to light stimulation. We then examine the eyes with a microscope, which is mounted on a platform that has a narrow slit of light emanating from it. (The instrument is known as a “slit lamp.”) We project the slit of light into the eye and this allows us to see an optical cross section of the eye anatomy. We can determine many things with this microscope including the presence of cataracts, the status of the iris and its relationship to the cornea; whether or not there is inflammation in the front of the eyes; whether or not there are foreign bodies in the eye, and with the aid of a magnifying lens, we can see a three-dimensional view of the optic nerve and retina.
In addition, an instrument known as a direct ophthalmoscope is routinely used to inspect the retina. Another instrument known as the indirect ophthalmoscope is sometimes used to inspect the far peripheral areas of the retina to look for retinal tears or detachments. With these instruments we can see remarkable details of the retina (the tissue in the eye which perceives images like the film of a camera). The retina appears as a delicate reddish-orange tissue, while the optic nerve looks like a white round disc. Tiny reddish blood vessels course on the surface of the retina and examining them can help diagnose conditions like diabetes or high blood pressure.
One other commonly used instrument is known as a perimeter. This is a white bowl-shaped device into which the patient stares at a central target. Small dots of light randomly appear in the peripheral part of the bowl. When the patient perceives the lights, they push a hand-held button to register their perception. This test is very helpful in following patients with glaucoma, strokes and patients with brain tumors.
There are, of course, many other tools and instruments used to assess the health and function of the human visual system. But those mentioned here are used the most frequently during routine eye examinations.
Dr. Dodd, an ophthalmologist, practices at Maryland Eye Associates located in Annapolis and Prince Frederick. He also is an instructor at the University of Maryland Department of Ophthalmology. He can be reached at 410.224.4550 or firstname.lastname@example.org