by Paul Chous, MA, OD, Doctor of Optometry
Now that we have considered the various kinds of diabetic eye disease, the treatments available for each, the results of clinical research, and some recommendations for avoiding or minimizing eye complications, let’s discuss the elements of a thorough diabetic eye examination.
It is unlikely that any two eye doctors (or any kind of doctors) will conduct an examination in exactly the same way. Procedures, techniques and explanations that work well for one health care provider may not work for another, and vice versa. Here, it is simply my aim to describe and explain the fundamentals of an eye exam that will allow you to ask the right questions and assess the thoroughness of your examination experience.
All eye examinations should start with a detailed case history. Patients often ask why so much general health information is required for an eye examination, and the answer is really quite simple: Because the eyes are connected (via the blood stream and nervous system) to every part of the body, and because the eyes and vision are affected by many general health conditions, medications, and genetic influences which are shared by or inherited from your family members.
Diabetics, in particular, should be asked about how long they have had diabetes, the specific medications they are using for diabetes treatment, the previous diagnosis of any diabetes complications (eye, kidney, nerve or vascular), the frequency and range of home blood glucose readings, the most recent home reading, and the results of their last glycosylated hemoglobin test.
The answers to these questions will give the eye doctor a good sense of overall diabetes control and the likelihood of finding eye complications. The patient’s responsibility is to know the answers to these very important questions.
After conducting a case history, the patient is typically asked to read the eye chart wearing any corrective lenses previously prescribed. This is not a test, nor anything to be embarrassed about if the letters are unclear. Guessing is absolutely allowed, as the true definition of visual acuity is the smallest letters that can, just barely, be identified correctly.
The results allow the doctor to gauge just how far off the prescription might be, or the effects of any eye diseases (cataracts, diabetic retinopathy, keratopathy, to name just three of many possibilities) that will be uncovered in subsequent parts of the eye exam.
A test of stereopsis (stereo vision, or the ability to see three-dimensionally) may be given, which precisely measures depth perception and helps evaluate how well the two eyes work together. Color vision testing also may be performed. In my experience, this is an important test, as academic research (including a study in which I participated while in optometry school) shows that diabetic retinopathy can cause short wave length (tritan, aka blue/yellow) color vision defects. In fact, some researchers believe subtle, acquired color vision deficiencies may precede the earliest stages of diabetic retinopathy by months to years.
I have consistently uncovered blue/yellow color vision deficits in long-standing diabetic patients without ophthalmoscopically detectable retinopathy, primarily through use of short wave length automated perimetry (SWAP), a sophisticated visual field test that isolates function of the retina’s blue/yellow cones (S-cones).
The patient’s pupil reactions should be evaluated by shining a bright light into each eye. This checks the neurological integrity of the connections between the optic nerve and the brain, and many optic nerve diseases (including advanced glaucoma and ischemic optic neuropathy) may be first detected this way. Many diabetics are found to have sluggish pupil responses, and this suggests some degree of autonomic neuropathy affecting Cranial Nerve III.
The patient also is asked to follow a moving target with her eyes only, which allows the doctor to evaluate the function of the six extra-ocular muscles and assess any possible paresis or double vision from diabetic nerve palsy.
A test of peripheral vision may be given, which may be as simple as detecting the number of fingers the examiner is holding up, or as sophisticated as a computerized visual field test that more precisely determines the extent and sensitivity of a patient’s peripheral vision in relationship to thousands of other patients (a normative database). All patients, diabetics included, should have their visual field checked by professional examination regularly, as visual field loss can be very subtle until severe damage has occurred (as in glaucoma). Such testing also represents the least expensive and invasive technique for assessing the integrity of the entire visual pathway (from eye to brain) and uncovering much serious neurological disease.
At some point, the patient will be refracted, the process through which a new eyeglass prescription is determined (“tell me which lens choice is better, choice #1 or choice #2"). No part of an eye examination is probably more frustrating to patients than this test: Oftentimes, neither of the two choices is clear, or both choices look identical. Take heart -- this is entirely normal; the test intentionally forces the patient to pick between crummy choices or choices that look virtually the same. Also, no one answer counts very much at all. The examiner is looking for consistency and will show the same choices repeatedly (even though you may not be aware of it!). When the test is completed, the prescription almost always is correct, and vision will be as clear as the patient is capable of seeing. If the doctor is a sub-specialist, such as a retina or glaucoma sub-specialist to whom your regular eye doctor has referred you, refraction may or may not be done.
Several points about refraction should be of particular interest to diabetic patients. Changes in blood sugar can have a dramatic impact upon your prescription, so it is important you and the doctor know if your overall blood sugar control is good (as reflected by recent HbA1c testing), and if your blood sugar level the day of the eye exam is high, low or relatively normal (as reflected by home blood glucose testing that day). Dramatic prescription changes may be the result of poor glycemic control, which should be corrected before getting a new eyeglass or contact lens prescription.
Diabetics sometimes have more difficulty than usual discriminating between the various choices presented during refraction. This may be due to loss of contrast sensitivity from keratopathy, cataract, or retinopathy. (I personally prefer to perform a specialized test of contrast sensitivity on all diabetics.) Decreases in nearsightedness, or increases in farsightedness, especially in one eye more than the other, are often signs the patient has diabetic macular edema and should alert the patient and doctor to this possibility.
All patients should have their eyes examined by a slit lamp, a specialized microscope that gives the examiner a highly magnified view of the eyes. The patient places her chin on a chinrest, and a bright (slit of) light is shined on various parts of the eye, including the cornea and conjunctiva, the iris, the lens, the anterior vitreous, the tear ducts and the eyelids. This allows the doctor to detect any sign of diabetic cataract, keratopathy, abnormal blood vessel growth on the iris (the cause of neovascular glaucoma) or blood cells that might signal vitreous hemorrhage. A fluorescent dye may be dabbed into the eyes, which is especially useful for detecting keratopathy of the corneal epithelium. Measurement of intraocular pressure (tonometry) also may be performed with this instrument, a similar hand-held device, or a machine that blows a puff of air at the cornea. Examination of the eye’s internal drainage canal, with a specialized, mirrored contact lens, may also be performed at the slit lamp microscope.
Eye drops should be placed into the eyes that dilate the pupils. Drops typically take 15 to 30 minutes to work, cause blurred vision and make patients more sensitive to light. Once the pupils are dilated, the internal eye is examined once again with the slit lamp microscope, very powerful hand-held lenses, or other instruments which allow the doctor to visualize the posterior vitreous, optic nerve and retina in considerable detail. A combination of techniques and instruments is often used to ensure completeness. Use of the slit lamp microscope to view the retina and optic nerve is very important, because the doctor is able to use both eyes to examine the patient in stereo (3-D), a feature which is critical for assessing diabetic macular edema, as well as optic nerve cupping from glaucoma.
The eye doctor may recommend other tests depending upon the patient’s particular diagnosis, including retinal or optic nerve photographs to document baseline findings and subsequent changes, more sophisticated visual field testing, or a retinal dye test called fluorescein angiography (a fluorescent dye is injected into the vein of a patient’s arm, and travels to the blood vessels of the retina which are photographed, allowing the doctor to evaluate retinal circulation).
After all tests have been completed, the eye doctor should explain the findings and treatment recommendations to the patient in understandable detail, and ensure the patient’s questions are answered. Sometimes, the patient may be referred to an ophthalmic sub-specialist for further evaluation.
At the conclusion of the eye exam, every patient should know her diagnosis, be informed of various available treatment options as well as the doctor’s recommended treatment plan, the prognosis for her condition, and exactly when she should have an eye examination again.
For the diabetic patient, special emphasis is placed on those findings pertaining to diabetic eye disease. The doctor should discuss the need for prescription lenses, including any changes in prescription, particularly as those changes relate to diabetic cataract or retinopathy. The patient should be advised as to the presence or absence of any eye muscle abnormalities due to diabetic cranial neuropathy, as well as the presence or absence of diabetic keratopathy, cataract, glaucoma or other optic neuropathy, and retinopathy or other retinal abnormality.
If diabetic eye disease (or any eye disease) is detected, the doctor’s recommendations and treatment plan should be explained in detail (written instructions are ideal), the next appointment date should be established (always one year or less) and a letter describing the patient’s eye exam findings should be sent promptly to each of her doctors. All of the patient’s questions should be encouraged and answered, and the doctor’s availability to answer future questions firmly established.
It is the eye doctor’s professional and ethical responsibility to be thorough, knowledgeable, and caring, and to know her limits if there is some aspect of a given patient’s care with which she is not totally familiar and comfortable. Consulting with a diabetic patient’s other health care providers, or referring that patient to another eye doctor who has more experience with a particularly unusual or difficult problem, are not signs of inexperience, but of excellent professional judgment.
I will close this discussion with some key questions that I believe every patient with diabetes should ask her eye doctor:
1. Do you have a lot of experience with diabetes and its various effects on the eyes?
2. Do you (or do other doctors in your practice) have any special interest in diabetic eye disease?
3. Do I have any signs of diabetic eye disease? Do I have any cataract, glaucoma, corneal problems, retina problems or eye muscle problems that are being caused by diabetes?
4. Has my eyeglass prescription changed significantly? If it has, is it likely caused by poor blood sugar control?
5. If I don’t have any diabetic eye disease, when do you want to see me again?
6. If I do have diabetic eye disease, how do you recommend we manage or treat it? When do you want to check my condition again? Are you experienced with the surgical or laser treatment of diabetic eye disease? If my condition worsens, will you refer me to a sub-specialist?
7. Do you have any recommendations on how to avoid or reduce eye complications from diabetes?
8. Will you send a report of your diagnosis and recommendations to my other doctors? Would you like me to ask my diabetes doctor to send you a report of her findings and recommendations?