As part of my job at an optometry clinic, I run patients through a series of tests which screen for common ocular and visual disorders and provide the doctor with important information prior to the eye exam.
This routine has become proceduralized, enough so that I can have a relatively coherent conversation while running and documenting all the tests, and yet there are two distinct situations which rise above the mundane and give me an opportunity to pause and reflect.
Stereo #9: a striking display of subconscious knowledge
The image of the world given by each of the two eyes is slightly different than the other. The brain uses this discrepancy to get a sense of the depth of the world, an ability known as stereopsis.
To test stereo vision, the patient wears a pair of glasses which allow different waves of polarized light to pass through each lens. Then, they’re given a chart of nine diamonds, each of which contains four dots. With the help of the glasses, one of these dots should appear to be popping out of the page. This test is known as the random dot stereogram.
The nine diamonds get harder as they go: number one is so clear that most patients can make it out even without the glasses, but on average, patients will be unable to make out any difference past number seven.
Number nine is a notorious diamond. In some cases, for what may be called stereoptically gifted patients, the correct answer is immediately discernible — the dot on the right is popping out. In most cases, however, the patient will hesitate for at least a few seconds.
When a patient gives up on number nine, I got into the habit of encouraging them to guess. I found, to my surprise, that a majority of patients — about 90% — are able to guess correctly. It got to the point where I specifically went out of my way to ask the patient: are you completely unaware of any difference between the dots? They would answer yes: despite that, they would go on to pick the right dot.
When, early onto this process, I asked the patients how exactly they made their decision, they would look at me strangely. After all, I had asked them to guess, which entails by definition that there was no guiding logic or reasoning used to arrive at their answer. But my question, stupid as it was, reflects my complete astonishment that what appears to the patient as a purely random choice is consistently the correct answer.
What’s going on here? The mystery of stereo #9 resembles a well-known funding in neuroscience called blindsight. Patients who’ve sustained damage to their visual pathways and are completely blind can nonetheless tell the difference between some images, say an X and O, at better-than-average chances. The running theory is that, although no visual information is available to their conscious mind, something about the stimuli is influencing their guesses on a subconscious level.
When the patient guesses on the ninth diamond on the stereogram, a similar thing is happening. The visual information which leads them to the correct answer isn’t discernible to their consciousness — but this doesn’t prevent it from existing.
So stereo #9 represents, to the optical technician, an enduring reminder of the existence of an unconscious domain of knowledge, and the undeniable influence it has on our behavior.
The handheld tonometer: a minor bioethical dilemma
A screening test which weighs heavily on the mind of the optometry patient is the air-puff test. This test, which is known officially as air-puff tonometry, administers a slight puff of air to the eye while measuring the resulting curvature of its front surface, thereby measuring the intraocular pressure.
At the optometry clinic where I work, we forego the dreaded air-puff tonometry for a handheld device. This device is unanimously better received by patients, and in stark contrast to the air-puff, which results in an extremely startling and uncomfortable sensation, it gives nothing but a slight brushing feeling to the eyes, as if there was only an eyelash caught in it.
There’s one complicating factor, however. If you investigate the two tests in depth, you find that the handheld tonometer is actually much more brutal than the air-puff. Whereas the air-puff makes no physical contact with the patient, the handheld shoots out a tiny probe which touches the front surface of the eye repeatedly. Even worse, when loading the device with a new probe, it gives the appearance of a needle — a word which, even just mentioned in the same sentence as ‘eye’, is enough to disturb the squeamish.
As a general rule, the technician is obliged to give a brief description of each test before administering it, in order to sufficiently prepare and inform the patient. This, then, immediately prompts an important question. Should the technician be straightforward about the mechanisms of the handheld tonometer, namely, that it makes contact with the surface of the eye?
Although it may be considered a somewhat trivial matter, this issue has all the makings of a proper bioethical dilemma. Specifically, it questions the nature of disclosure between healthcare provider and patient. Whereas before, the model of healthcare interactions was a predominantly patriarchal one, with the doctor making the ultimate determination as to what information was important to reveal, modern health care has transitioned into a more cooperative culture which honors the autonomy of the patient, who has the right to be informed of the complete thought-process of the doctor. Under this framework, intentionally withholding information becomes problematic.
Equivocating as to the exact mechanism of the handheld tonometer, especially when the patient asks directly, would amount to a minor regression into the patriarchal model, insofar as the technician is making the determination that it’s better for the patient not to know. And yet, there are good reasons to do so. Patients are, without exception, made more uncomfortable when they understand exactly how the handheld tonometer works, and in these cases even they might admit that they would have preferred not to know.
An optometric reiteration of a perennial and decidedly human question: can the truth hurt us, and if so, are we right to obscure it?