When your headlights flash an animal in the road you see the bright orange reflex of light from the retina (pictured to the left).  While that was man’s first image of the interior of the eye the view is now down to the microscopic level.  The device which makes that possible is Optical Coherence Tomography or OCT. We can visualize early and subtle changes in the retina and optic nerve in many cases before they are noticed by the individual.

How is this done?  The patient is seated before the OCT machine and waves of safe invisible ultraviolet light are beamed into the eye.  The light is reflected back just as it is with the headlight.  The reflected light is captured by a sensing devise (interferometer) and passed along to a computer which interprets the variations in the reflection as various anatomic parts of the retina and optic nerve.

Anatomic Details of the Retina The complex structure of the retina, pictured here, passes the visual information along its nerves to the Optic Nerve which in turn feeds the image to the brain.  All this processing takes about 2/10ths of a second.  Needless to say, small anatomic problems in the retina can cause big problems with the vision.  So it becomes important to view the anatomic changes asssociated with disease early in their evolution.  This can also be said about diseases of the Optic Nerve such as glaucoma.OCT Image of the Retina

To the practiced ophthalmologist, the image to the right represents all the layers of the retina in sideways view.  One can see early signs of macula degeneration, swelling due to diabetes or other circulatory problems as well as impending holes.

Diabetes can have a devastating effect on vision if it is allowed to progress unchecked.  There is emerging new information about the best ways to manage the condition.  Clinical studies have shown that the proper control of blood sugar levels as well as blood pressure and cholesterol can delay or even stop the progression of diabetic retinopathy. 

Hemaglobin A 1c (HbA1c) is the correct way to assess the level of blood glucose.  The test measures the average level of glucose to which the blood cell has been exposed over its life so you are getting a summary of the blood sugar, not a momentary view as you would get with a single blood sugar measurement.  Patients with type 2 diabetes should have a HgbA1c of 6% to 7% (normal levels are 4% to 5.9% in healthy people).  In addition, blood pressure should be maintained below 130/80.

Studies have demonstrated that very small differences in the management of the disease can have a profound effect on the vascular complications of diabetes.  One study (Diabetes Control and Complications Trial) showed that in a group of young diabetes managed in the usual way with glucose measurements and insulin injections twice a day versus a group having measurements three times a day with accompanying insulin, there was a five times greater risk of worsening of the diabetic retinopathy.

People with diabetes should have an ophthalmic exam once a year.  If they develop mild to moderate retinopathy the exam should done every six months and every two to four months if the vision has been effected by macular edema or prolifertive retinopathy.  While the exam should include measurement of the vision, it is not always an effective way to determine the condition of the retina.  This is because there are many factors which effect the vision other than the diabetes.  If there are any signs of progression a fluorescein angiogram should be obtained.  This is a photographic assessment of the retinal blood vessels.

There are numerous trials under way to identify the best means of treating diabetic retinopathy but the gold standard at this time is panretinal laser photocoagulation (PRP).  This technique creates numerous small laser burns in the retina and has been shown to slow or stop the progression of the disease; it will not undo prior damage.  This technique has been around for forty years, the only change has been the light energy delivery system.  In my training at Medical College of Virginia, some of the pioneering work was being done.  In the early years, the light energy was collected from a huge airport searchlight and narrowed down to a fine beam that would pass through a pupil and into the eye.  Now an Argon laser is the size of a desktop computer.

Studies have shown that only 7% of diabetics reach optimum control of HbA1c, blood pressure and cholesterol and so there is a good chance that an effected patient will worsen over time.  It is therefore important that diabetics seek out quality eye exams on a regular basis.