Visual Acuity, Visual Perception, Adaptation, and Tolerance:
A Case Study that Perplexes
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As eye care professionals, our main focus for our patients is to improve their vision. Naturally, this improvement can be by optical aids, medications, or by surgical means. I am sometimes surprised by the patients who come to us unaware that they have significantly reduced vision.
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I am not talking about a patient who has waited a year or two in order to get new glasses in order to correct a small amount of nearsightedness, farsightedness, astigmatism, or
presbyopia. There are plenty of people functioning well with 20/30 or 20/40 uncorrected vision even though their vision can be improved with glasses or contact lenses. What I am referring to are those people who walk into your office after they have failed the driver’s license eye examination. These are the people with 20/400 vision in one eye and 20/80 in the other. They are people who are driving or operating machinery or equipment. They have never bothered covering one eye to compare the vision between their eyes.
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After the driving test, they realize that it is clearer in one eye and blurry out of the other. There are certainly some “neurological comfort zones” that people adapt to with their vision. There are adaptation and tolerance issues when prescriptions are prescribed or when it comes to ranges of clear vision. But when a patient’s vision is so out of focus and so blurry, we have to scratch our heads sometimes and ask, “How can they think it is clear when it is not?”
This case study should be enough of a reminder as to why we care for human eyes. What you hear or what you see as an ECP sometimes can make no sense until you unravel the mystery. It is a lesson in why visual acuity, patient perception, adaptation, and tolerance can really surprise you.
I received a phone call from Mr. Jones concerning his wife. Mr. Jones was a patient of mine while his wife was not. Mr. Jones said that his wife had noticed some irritation during the prior evening in her left eye. The left eye was swollen and Mrs. Jones had used some GenTeal drops and cool compresses during the night, but it was still bothering her. Mrs. Jones is a 78 year old white female with hypertension. She had last seen an ECP three years ago and there was nothing remarkable concerning her eye history, according to her. She was wearing photo grey extra glass progressive lenses.
When she entered the exam room, it was obvious that her left upper eyelid was swollen and the left cornea appeared to be slightly cloudy. Her pupils seemed to be unequal with a larger OS pupil. Mrs. Jones’ presenting visual acuity with her glasses was OD: 20/80 and OS: Light Perception! Her examination under the biomicroscope showed cortical cataracts and nuclear sclerosis cataracts in both eyes, a cloudy cornea OS, very narrow angles OU, a swollen, ptotic eyelid OS, and her left pupil was fixed and dilated. There was the presence of granular material present on the capsule of the left lens. There was little to no view of the posterior poles. Upon checking her intraocular pressures with a non-contact tonometer, her IOP’s were OD: 18 and OS: 60 mm Hg @ 12:30 PM.
This was an obvious emergency situation. I immediately made a phone call to an ophthalmologist who saw her an hour later. As I escorted the Jones’ to their car, I advised Mr. Jones to keep Mrs. Jones near to him. Falls among visually disabled elderly people are quite common and Mrs. Jones had a major vision problem. She did not need a hospitalization for a broken leg or hip to compound her vision problems. My instructions to her were, “take baby steps and be extra careful with everything until I see you again. And absolutely no driving!”
As ECPs, we usually care for and manage primary care problems. Many questions entered my mind concerning Mrs. Jones including: what happened at her eye exam 3 years ago, what was her visual acuity 3 years ago, was she advised that her angles were narrow and that there may be a risk of narrow angle glaucoma, what were her intraocular pressures 3 years ago, would a laser iridotomy within this 3 year period have saved her vision in her left eye, and how bad were her cataracts 3 years ago?
I was also startled by the fact that this intelligent woman allowed her vision to get so bad in one eye without noticing it. She was shocked when I covered her right eye and she could not see the eye chart out of her left eye. Not only could she not see it, but she could not count my fingers at 3 feet, and could not see my hand move in front of her. And, how does one function safely with 20/80 vision out of the better-seeing eye? She was literally one step away from having no light perception or blindness in her left eye and was oblivious to that fact.
I spoke to the ophthalmologist during her appointment. He indicated that her problems included a closed angle with a brunescent cataract, and pseudoexfoliation of the lens capsule of the left eye. A B-scan was performed showing no retinal detachment or tumors present in the posterior segment of the left eye. Cosopt, atropine, and pred acetate drops were prescribed for the left eye BID. She will be following up with the surgeon in order to determine the next course of action as the left eye quiets down. She will also be going back to the ophthalmologist in November for another medical/surgical evaluation of both eyes.
I saw her again in order to improve her vision in the right eye. Her refraction was OD: -0.25-2.25 X 180/ Add +2.50. Her visual acuity OD was 20/60, J1 corrected. I plan to update her prescription with polycarbonate Transitions lenses and place a temporary balance lens in front of her left eye. We discussed the fact that cataract surgery will be in her future for the right eye. The decisions for the left eye are on hold for now. She did indicate to me that her left eye felt much better now that the pressures have come down into the 30’s, which is still too high. It was certainly an improvement from pressures of 60! Cataract surgery on the left eye may help reduce the IOP and may allow more light to enter the eye. The visual outcome may be “guarded” at best, but I am hoping for some improvement in her left eye.
One’s visual acuity and visual perception are inter-related when it comes to seeing and vision. According to the Dictionary of Visual Science, visual acuity is defined as “acuteness or clearness of vision which is dependent on the sharpness of the retinal focus, the sensitivity of the nervous elements, and the interpretative faculty of the brain. Visual acuity varies with the region of the retina stimulated, the state of light adaptation of the eye, general illumination, background contrast, the size and the color of the object, the effect of the refraction of the eye on the size and the character of the retinal image, and the time of exposure.”
The Dictionary of Visual Science also defines perception as “the appreciation of a physical situation through the mediation of one or more senses.” Awareness, experience, and cognition will affect visual perception. There are some psychological affects that will affect visual perception. According to the Webster’s Dictionary, adaptation is defined as “adjustment of a sense organ to the intensity or quality of stimulation.” Tolerance is defined as “the relative capacity to endure or adapt physiologically to an unfavorable environmental factor or the allowable deviation from a standard.”
In this case, visual acuity, perception, adaptation, neurological abilities, and psychological behaviors played a role in Mrs. Jones ability to “function” until she reached a point where these connections eventually broke down and she sought help. Some questions for this case will remain a mystery. As human beings, we are able to adapt to situations that under other circumstances would be totally unacceptable. Why did Mrs. Jones suddenly one night become aware that there was a problem in her left eye? If there was not the problem of her pressures and glaucoma, how could she have seen through 3+ cortical cataracts and nuclear scleroic cataracts? How could she have thought that her vision was “ok” when the pressures in the left eye were damaging the optic nerve? And she was “functioning,” watching TV, reading, and driving! At least, she thought that she was “functioning.” For anyone else, this situation would have meant a call to the ECP years ago.
This is still the most dramatic case that has ever entered my office. It was dramatic because there were so many problems within one eye. A significant cataract, by itself should have been enough of a problem that the patient sought care. Corneal swelling by itself should have been the same. Intraocular pressures of 60 mm Hg should have been an even more urgent problem than either of the above two issues. Yet, this patient needed all three significant problems in order to seek help and even then the help was sought by her husband. I wish that I had seen Mrs. Jones several years ago. It may have prevented the problem that she now will have for the rest of her life. Education, awareness, and preventative care presumably could have gone a long way on the part of her previous ECP.
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