Most people think the result of an eye examination is a prescription. A few numbers, some letters and perhaps a recommendation for new glasses if those numbers have changed.
The prescription is important, obviously, but it is only one answer to one question. By the time you leave the testing room, your optometrist has gathered far more information than could ever fit on the rather underwhelming piece of paper you take home.
Even finding the prescription is more complicated than making the letters on the chart as sharp as possible. If that were the only objective, the job would be relatively straightforward. The optometrist is trying to find the clearest and most comfortable prescription, and those two things do not always arrive at precisely the same answer.
Giving somebody a tiny amount of extra minus power, for example, might make the smallest letters look fractionally sharper in the consulting room, but it can also make their eyes work harder than necessary. This is particularly relevant for younger people, whose eyes may happily accept more power during the test and then spend the rest of the day objecting to it.
That is partly why you spend what feels like several months being asked, “Which is better, one or two?”
Your answers are doing more than gradually assembling a prescription. The optometrist is checking whether they are consistent, whether the result makes sense alongside everything else they have found and whether today’s measurement is likely to produce comfortable vision outside the very peculiar circumstances of sitting in a darkened room reading letters from a wall.
This becomes especially important when the prescription has changed, because not every alteration should immediately become a new pair of glasses. If the difference is tiny, there is a judgement to make about whether changing it will produce any useful improvement in real life or merely solve a problem the person had not noticed until somebody showed them a slightly sharper letter.
A prescription does not exist by itself. It belongs to somebody who drives, reads, works, cooks, paints, spends ten hours staring at three computer screens or mainly needs their glasses to identify the correct bus before it disappears down the road.
The examination is also checking the health of the eyes, which tends to receive less attention because there is no exciting frame selection involved afterwards. At Doctor Oculus, we use fundus photography to record the appearance of the retina, blood vessels and optic nerve at the back of the eye.
Looking through the eye with an ophthalmoscope remains an important part of the examination, but a photograph gives us something else: a record. If a blood vessel, mark or optic nerve changes gradually over several years, comparing images is considerably more useful than asking an optometrist to remember exactly what it looked like on a wet Thursday afternoon in Digbeth two years later.
Most changes within the eye happen slowly, so the comparison can be as important as the photograph itself. Something that looks unusual may have remained exactly the same for years and simply be normal for that person. Something that looks fairly ordinary in isolation may deserve more attention if it has altered since the previous examination.
Then there are the problems that no machine can explain on its own.
Somebody may arrive convinced that they need stronger glasses because reading has become difficult, only for the examination to show that their distance prescription has hardly changed. That does not mean the problem is imaginary. It means the explanation probably lies elsewhere.
Perhaps they have reached the point where reading glasses or varifocals would genuinely make life easier. Perhaps they work at a computer all day and an occupational lens would be more useful than a general-purpose pair. Their existing glasses may have slowly worked their way down their nose, leaving them looking through a different part of the lens from the one originally measured. The lenses may also be badly scratched, the frame may no longer fit properly or their visual demands may simply have changed since the glasses were made.
None of that appears in the prescription.
The opposite can happen too. Somebody may have a noticeable change in prescription but be perfectly comfortable in the glasses they already own. If the new result offers very little practical benefit, there is a sensible conversation to be had about whether replacing them is worthwhile yet.
People are often surprised by this because they assume an eye examination is the first step in the ritual that inevitably concludes with buying glasses. Quite often, the useful result is reassurance that the eyes are healthy, the prescription is stable and there is no pressing reason to change anything.
That is one of the advantages of having enough time to talk to people properly. The purpose of the examination is not to make every result fit neatly into a sales process. It is to work out whether the prescription explains whatever brought the person through the door in the first place.
By the end of the test, we may know whether the eyes are healthy, whether the vision has changed and whether that change is likely to matter. What we do not yet know is what the person actually needs their glasses to do.
There is no machine for that bit.
A person who drives for most of the day may need something completely different from somebody working between several computer screens. A keen reader will not necessarily value the same things as somebody who spends weekends cycling, and the person restoring an elderly motorcycle in a dim garage has different visual requirements from somebody painting watercolours beside a sunny window.
Two people can have exactly the same prescription and need entirely different glasses. Even the same person may need more than one solution because seeing clearly across a meeting room, at a computer and underneath a kitchen cupboard are three separate optical jobs, despite all taking place within the same general human life.
That is the part of an eye examination people rarely talk about. Finding the prescription is one part of the science. Understanding what should be done with it requires the rest of the information, some experience and a proper conversation.
The eye examination is not the end of the process. It is the point where we finally know enough to start giving useful advice.