I have just examined one of my patients. He complained of poor distance vision when wearing his glasses which were suppled by me three months ago. His last prescription was -2.00 DS in each eye and this gave 6/5 in each eye. Today he is -3.00 DS in each eye and this gives him 6/5 in each eye. He drives for a living and cannot see well enough to drive safely with his current glasses. He is 25 years old, is overweight and taking medication for high blood pressure and has no other health problems. What is going on?
It sounds very much like your patient has type 2 diabetes. Elevated blood sugar can produce changes in the crystalline lens, altering clarity, refractive index and curvature. Refractive shifts are in the myopic direction although aggressive attempts at controlling blood sugar can cause hyperopic shifts. The sudden onset and significant dioptric change over a short period of time, helps differentiate diabetic involvement from physiologic refractive changes that naturally occur in myopes and hyperopes. The cause of the refractive shift is not totally understood but may involve osmotic dehydration of the crystalline lens.
The patient needs three things. Firstly, an explanation of your suspicions. Secondly, a referral to a medical practitioner with expertise in diagnosing and treating diabetes. Thirdly, a new pair of glasses with the stronger prescription in order to be able to drive safely and keep working. Refractive stability typically takes around six weeks and as his blood sugar returns to normal levels, the myopia will return to around -2.00 DS in each eye.
It is important to counsel the patient and let him know that glasses to the new prescription are a temporary measure, that you are trying to help him get through the six week stabilisation period and help him continue his work during that period.
The temporary nature of this prescription may influence frame and lens choice as these are directly related to the cost of the temporary glasses.