In medical offices all over the country patients are patiently squinting down corridors to spot the color bars, letters, and symbols on a faded cardboard chart.
First covering one eye, then the next, standing a measured distance of seven paces away. The overhead lights flicker, distractions come and go, and finally the eye exam is done. These same patients then think they are on safe ground (or thick ice, as we say in Canada).
A common assumption is that annual physical exams with the doctor preclude worries about vision because one is tested by the doctor’s staff each year. The problem I have with this is that we cannot cover nearly enough with the simple Snellen eye chart. About all it tests for is visual acuity and color blindness (and from twenty feet away, not the standard computer screen distance of less than two feet), and there are certainly many better ways to determine both of these conditions and more.
The modern state of the art of eye inspection requires hundreds of thousands of dollars of machines that fill a small room. In addition to the very rough estimate of the faded old wall chart, the modern optometrist can test for the following important conditions:
1. Visual acuity: by using letters with measured lighting projected on the wall of a darkened examining room, the examiner gets a much more accurate reading than the hall chart. This is where nearsightedness or far-sightedness show up, and prescriptions for glasses can be initiated.
2. Curvature of the cornea: By using special lenses to fine tune the acuity testing, the examiner can determine if there is any astigmatism. Not only can this be tested for, but the readings are accurate enough to incorporate into the prescription for new glasses lenses.
3. Pressure of the eye: Glaucoma can NOT be discovered on a wall chart, only by testing for pressure directly. The eye examiner uses freezing drops to keep you from flinching, then puffs a jet of air at close range through a blue circle almost touching the cornea. Further testing can also be done by a hand held tonometer, but usually the computerized method is preferred as a screening device.
4. Tear production: With the aid of some orange staining and a strip of paper, the production of tears can be measured accurately.
5. Fine examination of the surface: the cornea comes under huge magnification and spectacular detail when seen through a slit lamp. In addition to corneal abrasions, foreign bodies, or ulcerations, one can also see the state of the mebothian glands on each edge of the eyelids. A common cause of dry eyes occurs when these glands get plugged with dry wax, and effectively “scratch” the eyes every time one blinks. Invisible on regular clinical exam, these are easily detected under proper magnification. Treatment can be as simple as warm compresses to melt the waxy deposits.
6. State of the lens: cataracts (fogging of the eye’s lens) are effectively invisible in their early stages unless one uses proper lighting and magnification from a slit lamp.
7. Retinal damage: Without proper dilation, the full retina is difficult to visualize. With the proper modern equipment not only can one see the retina better, but further tests can be done where trouble is found. For example, computerized machines can test for retinal thinning, visual field “blind spots”, and photographic measurements of the optic nerve and other key areas.
So to get a modern screening of your own eyes, it is best to see an optometrist every couple of years, as a base line for adults.
If any problems are found, then further investigations at more frequent intervals might be suggested, or further assessments could be recommended with an opthalmologist. But do not think that the old-fashioned eye exam from your doctor will prevent or detect most eye diseases. Please get your eyes checked the new-fashioned way!