Why do diabetic patients have fluctuating vision?

Blood sugar changes cause the crystalline lens to absorb or release water, changing its thickness and refractive power. High blood sugar can cause lens swelling and a myopic shift. When blood sugar normalizes, the lens returns to its original shape, causing a hyperopic shift. This is why prescriptions should only be updated after blood sugar has been stable for 2-3 weeks.

What is the difference between NPDR and PDR?

Non-proliferative DR (NPDR) involves damage to existing retinal blood vessels, causing microaneurysms, hemorrhages, and exudates. Proliferative DR (PDR) involves the growth of new, abnormal blood vessels (neovascularization) that can bleed into the vitreous or cause retinal detachment. PDR is more severe and requires aggressive treatment.

How often should diabetic patients have eye exams?

Diabetic patients should have a comprehensive dilated eye exam at least annually. Type 1 diabetics should begin screening 5 years after diagnosis. Type 2 diabetics should be screened at the time of diagnosis since retinopathy may already be present. More frequent exams may be needed if DR is detected.

Diabetic Retinopathy for ABO

What Is Diabetic Retinopathy?

Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus that damages the retinal blood vessels. It is the most common cause of blindness in working-age adults (20-65 years). Both type 1 and type 2 diabetes can cause DR, with risk increasing with duration of disease and poor blood sugar control.

Stages of Diabetic Retinopathy

Non-Proliferative Diabetic Retinopathy (NPDR)

NPDR involves damage to existing retinal blood vessels without new vessel growth. It progresses through stages:

Stage	Findings	Vision Impact
Mild NPDR	Microaneurysms (small vessel bulges)	Usually none
Moderate NPDR	Dot/blot hemorrhages, hard exudates, cotton-wool spots	May be affected if macula involved
Severe NPDR	Extensive hemorrhages, venous beading, IRMA	High risk of progression to PDR

Proliferative Diabetic Retinopathy (PDR)

PDR is the advanced stage where retinal ischemia (oxygen deprivation) triggers the growth of new, abnormal blood vessels (neovascularization) on the retinal surface or optic disc. These fragile vessels can:

Bleed into the vitreous (vitreous hemorrhage), causing sudden vision loss
Form fibrous tissue that contracts and causes tractional retinal detachment
Grow on the iris (neovascularization of the iris, NVI), potentially causing neovascular glaucoma

Diabetic Macular Edema (DME)

DME can occur at any stage of DR and is the most common cause of vision loss in diabetic patients. Leaky retinal vessels allow fluid to accumulate in the macula, causing thickening and reduced central acuity.

NPDR involves damage to EXISTING vessels (microaneurysms, hemorrhages, exudates). PDR involves growth of NEW abnormal vessels (neovascularization). The transition from NPDR to PDR marks a critical escalation in disease severity requiring aggressive treatment.

Impact on Spectacle Prescriptions

Diabetes affects refraction in several ways that opticians should understand:

Fluctuating vision: Blood sugar changes cause the crystalline lens to swell or shrink, temporarily changing its refractive power. Patients may report their glasses work some days and not others.
Myopic shift: Hyperglycemia can cause lens swelling and a temporary increase in lens power (myopic shift). This is why new glasses should not be prescribed until blood sugar has been stable for at least 2-3 weeks.
Hyperopic shift: When blood sugar is brought under control, the lens may return to its normal state, causing a hyperopic shift.

Treatment

Blood sugar control: The most important factor in preventing and slowing DR progression
Anti-VEGF injections: First-line for DME and some PDR cases
Panretinal photocoagulation (PRP): Laser treatment for PDR; destroys peripheral ischemic retina to reduce VEGF production
Vitrectomy: Surgery for non-clearing vitreous hemorrhage or tractional retinal detachment

If a diabetic patient reports that their glasses suddenly seem too strong or too weak, do not rush to change the prescription. Ask about recent changes in blood sugar control or medication. Refractive fluctuations from blood sugar changes can mimic a prescription change. Advise them to achieve stable glucose levels before getting new glasses.

Thinking diabetic retinopathy only affects patients with advanced diabetes. DR can begin within 5 years of type 1 diabetes diagnosis and may already be present at the time of type 2 diagnosis (since type 2 often goes undiagnosed for years). Annual dilated eye exams are recommended for all diabetic patients.

Key Takeaways

Diabetic retinopathy damages retinal blood vessels; the leading cause of blindness in working-age adults
NPDR involves microaneurysms and hemorrhages; PDR involves neovascularization
Diabetic macular edema can cause vision loss at any stage
Blood sugar fluctuations cause temporary refractive changes; wait for stability before prescribing
Blood sugar control is the most important preventive measure