Diabetes mellitus is a group of metabolic disorders characterized by chronic hyperglycemia caused by defects in insulin secretion and/or utilization. Diabetes can lead to various ocular complications, including diabetic retinopathy (DR), cataracts, changes in lens refractive power, iridocyclitis, rubeosis iridis, and neovascular glaucoma.
Diabetic Retinopathy (DR)
Diabetic retinopathy is the most common vascular disease of the retina.
Diabetic Cataracts
Hyperglycemia can cause lens fibers to swell, degeneration, and opacification, resulting in the development of cataracts.
Refractive Errors
Elevated blood glucose levels may cause a shift from emmetropia to sudden myopia or reduce symptoms of presbyopia in previously affected individuals. The mechanism involves elevated blood glucose levels lowering the concentration of inorganic salts in the bloodstream, reducing the osmotic pressure of the aqueous humor. This allows aqueous humor to infiltrate the lens, increasing its curvature and, consequently, its refractive power. When blood glucose levels decrease, individuals may revert to emmetropia, but presbyopia symptoms may reappear, requiring the use of reading glasses again.
Iridocyclitis
Iridocyclitis is more commonly observed in juvenile diabetes.
Adult-Onset Diabetes and Open-Angle Glaucoma
Diabetes is associated with an increased risk of primary open-angle glaucoma. Patients with diabetes have higher intraocular pressure and an elevated incidence of open-angle glaucoma. It is thought that diabetes-related small vessel involvement may heighten the optic nerve's susceptibility to pressure-related damage.
Oculomotor Nerve Palsy
Diabetes is a common cause of oculomotor nerve palsy, which can result in sudden extraocular muscle movement dysfunction and diplopia. The pupil is typically unaffected, and gradual recovery is often possible.
Other Manifestations
Diabetic patients frequently exhibit reduced tear film stability, tortuous and dilated microvasculature of the bulbar conjunctiva, microaneurysms, decreased corneal sensitivity, abnormal pupillary function, abnormalities in the neural and vascular regulation of choroidal blood flow, ischemic optic neuropathy, and asteroid hyalosis.