By Dr. Hao Nguyen · · 3 min read
People book eye exams for eye reasons. Reading is harder, night driving is worse, the school sent a note. That is entirely reasonable, and it undersells what the appointment can do.
Every time we look at a retina we are looking at your circulatory system and part of your central nervous system directly, at high magnification, without a single incision. There is nowhere else in the body where that is possible.
Diabetes
This is the one we find most often. Persistently elevated blood glucose damages the walls of small blood vessels, and the retina is dense with exactly those vessels. The changes are visible before a patient has any visual symptom at all.
I have told patients they should see their physician about their blood sugar based on what I saw in a retinal image, and been right. It is not a rare event across a career.
For anyone already diagnosed, the annual retinal exam is the single most effective thing you can do to protect your sight, because diabetic retinopathy is entirely painless until it threatens central vision.
High blood pressure
Sustained hypertension produces characteristic changes in the retinal arteries: narrowing, altered light reflex, and where it crosses a vein, a visible nipping effect. In more severe cases there is haemorrhage and swelling.
Because these changes reflect what is happening in small vessels throughout the body, they tell a physician something a single blood pressure reading in a clinic does not. We refer when we see them.
Cholesterol and cardiovascular risk
- Deposits visible within retinal blood vessels, sometimes indicating material that has travelled from a carotid artery
- A pale ring around the cornea, which in a younger patient can indicate significantly elevated cholesterol
- Yellowish deposits on the eyelids, which are associated with lipid abnormalities
Autoimmune conditions
A number of autoimmune conditions produce inflammation inside the eye. Uveitis and iritis are associated with ankylosing spondylitis, inflammatory bowel disease, sarcoidosis and others, and eye inflammation is occasionally the first sign that leads to the underlying diagnosis.
Sjogren's syndrome frequently presents as severe dry eye long before it is formally diagnosed. Rheumatoid arthritis affects the eye in several ways.
Thyroid and neurological conditions
Thyroid eye disease produces characteristic changes to the position and movement of the eyes, and sometimes to the lids, which are visible on examination.
Neurological conditions show up in several ways. Swelling of the optic nerve head can indicate raised pressure inside the skull. Specific patterns of visual field loss point to particular locations along the visual pathway. Abnormal pupil responses and new double vision can both indicate a cranial nerve problem needing prompt investigation.
A sudden onset of double vision, a drooping eyelid, or a pupil that has changed size is not something to watch and wait on. Those warrant a same-day call.
Why this argues for annual exams
Almost everything described above is silent. It causes no pain and no blur. That is precisely why a scheduled look, rather than a symptom-driven one, is the only reliable way to find it.
It is also why we take our time. Two patients an hour rather than five or six is what makes room for a careful retinal examination rather than a quick refraction, and a careful retinal examination is where all of this is found.
The short version
- The retina is the only place a doctor can directly observe blood vessels and a cranial nerve without an incision.
- Diabetes frequently shows in the retina before it has been diagnosed, and before any visual symptom appears.
- Sustained high blood pressure produces characteristic arterial changes that reflect what is happening in small vessels throughout the body.
- Cholesterol abnormalities, autoimmune conditions, thyroid disease and neurological problems all have recognisable ocular signs.
- Sudden double vision, a drooping eyelid or a pupil that has changed size all warrant a same-day call rather than watchful waiting.
- Almost all of this is silent, which is why a scheduled annual look beats a symptom-driven one.
- We write to your physician when we find something systemic, because eye findings are far more useful to them than a description after the fact.
- None of this requires symptoms, which is precisely why an annual exam finds things that a symptom-driven visit never would.
- Bring a complete list of your medications, including over-the-counter products and supplements, since many of them have ocular effects worth knowing about.
Want the full detail?
Read about comprehensive eye examsThis article is general educational information, not medical advice or a diagnosis, and it is not a substitute for an examination. If you are experiencing sudden vision loss, eye pain or an eye injury, contact us immediately or go to an emergency room.
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