What actually happens in a comprehensive eye examination

A surprising number of people have never had a proper eye examination. They have had their sight tested — stood in front of a chart in a spectacle shop, read down until the letters blurred, and walked out with a prescription. That is a fraction of the job, and it is the fraction that misses the things worth catching.

A comprehensive examination by a licensed Doctor of Optometry takes between thirty and forty-five minutes. Here is what those minutes are spent on, and why each part is there.

History, before anything is measured

The conversation at the beginning is not small talk. Whether anyone in your family has glaucoma changes how closely we look at your optic nerves. Whether you have diabetes or high blood pressure changes what we expect to find at the back of the eye. Headaches, the medicines you take, the work you do, how long you spend driving at night — each of these points the examination somewhere specific.

Visual acuity, and then refraction

The chart measures how much detail you can resolve. Refraction works out the lens power that would improve it, and it is done in stages — an objective measurement first, which does not depend on your answers, then the subjective refinement where you are asked to compare one lens against another. The objective step matters because it catches the cases where the answers and the eye disagree.

How the two eyes work together

Each eye can be perfectly sharp on its own and the pair can still be a problem. Binocular vision testing looks at whether the eyes are aiming at the same point, whether they can hold that alignment through a long stretch of close work, and whether they focus together comfortably. A great many complaints of "eye strain" and "headaches after reading" come from here rather than from a refractive error, and no amount of lens power fixes them.

Eye pressure

Intraocular pressure is checked because raised pressure is the main modifiable risk factor in glaucoma. It is worth being clear about what the number means: normal pressure does not rule glaucoma out, and a slightly high reading does not mean you have it. It is one piece of evidence, taken alongside the appearance of the optic nerve and, where indicated, a visual field test.

The front of the eye

Under magnification, the eyelids, lashes, tear film, cornea, iris and lens are examined in turn. This is where dry eye is characterised rather than guessed at, where early cataract is graded, where the corneal scarring left by an old injury or infection shows up, and where the reason contact lenses have become uncomfortable usually becomes obvious.

The back of the eye

The retina and optic nerve are examined directly. This is the part of the examination most people have never had, and it is the part that finds things they did not come in for. The retina is the only place in the body where blood vessels can be seen without cutting anything open — which is why diabetic damage, the changes of long-standing high blood pressure, and the appearance of a nerve under pressure from glaucoma can all be identified here, often before the patient has noticed a single symptom.

Seeing it properly usually means dilating the pupils with drops. Your near vision will be blurred and you will be light-sensitive for a few hours, so it is worth arranging not to drive yourself home. The inconvenience buys a complete view instead of a partial one.

What you should leave with

You should leave knowing what your prescription is, whether it has changed, what was seen at the front and back of each eye, and when to come back. If anything needs watching rather than treating, you should know what is being watched and why. If you were referred onward, you should understand what for.

If none of that was explained to you, you did not have a comprehensive examination.

How often

For most adults with no symptoms and no risk factors, every two years. Annually if you are over forty, if you have diabetes or hypertension, if glaucoma runs in your family, if you wear contact lenses, or if you are of African descent — which raises the risk of glaucoma and lowers the age at which it tends to begin. Children should be examined before starting school and regularly through it.

Every practitioner in our register is licensed by the Optometrists and Dispensing Opticians Registration Board of Nigeria. You can find one practising near you through the chapter's directory.