This patient has cataracts: progressive opacification of the lenses with chronic loss of visual acuity.  Scattering of light within the lens leads to glare and halos around bright lights, especially at night.  Examination reveals cloudiness in the lens, decreased detail when examining the retina, and loss of the red reflex.

Transparency of the lens requires an ordered epithelial cell structure and maintenance of intracellular crystallins.  Aging and environmental stressors can disrupt transparency and contribute to cataract formation through the following mechanisms:

• Nuclear sclerosis: new layers of epithelia form on the cortex of the lens, compacting older layers beneath

• Photooxidative damage and cross-linking of crystallins causes brown/yellow pigmentary changes

• Osmotic injury resulting in development of hydropic lens fibers that degenerate

Cumulative photooxidative stress is worsened by heavy UV exposure (eg, outdoor occupations), smoking, or ionizing radiation.  Likewise, osmotic injury is accelerated in patients with diabetes mellitus.  A disordered balance of prooxidative versus antioxidative compounds in the lens (eg, decreased glutathione) may also contribute.

(Choice A)  In patients with diabetes, excess glucose is converted to sorbitol at a greater rate than sorbitol can be metabolized to fructose.  Osmotic injury due to the higher concentration of sorbitol in the lens can lead to cataract.  However, in patients without diabetes, the conversion of sorbitol to fructose is adequate to prevent the buildup of sorbitol.

(Choice C)  Photoaging of skin is characterized by decreased collagen fibril production and loss of tissue elasticity in sun-exposed areas.  However, defects in collagen production are not a significant contributor to cataract.

(Choice D)  Microvascular ischemia in patients with long-standing diabetes can cause neovascularization in the retina, leading to diabetic retinopathy.  Most patients are asymptomatic until late in the course of the disease, when vitreous hemorrhage or retinal detachment causes acute vision loss.

(Choice E)  Presbyopia is a type of refractive error caused by loss of the normal distensibility of the lens with age.  It reduces the ability of the eye to focus on near objects but does not cause loss of visual acuity.

Educational objective:
Cataracts are characterized by progressive opacification of the lens with chronic loss of visual acuity.  Aging and environmental exposures (eg, UV light) contribute to cataract formation by inducing nuclear sclerosis, photooxidative damage to lens crystallins, and osmotic injury.