Cataract

Cataract — any opacity of the crystalline lens — is the leading cause of reversible blindness worldwide and the most commonly performed surgical procedure in medicine. Age-related cataract is the dominant form, but secondary cataracts (from corticosteroid use, uveitis, diabetes, trauma, and radiation) are clinically important and often present earlier. Phacoemulsification with IOL implantation is the definitive treatment; the modern optometrist's role extends well beyond detection to include surgical counseling, IOL selection discussions, preoperative ocular surface optimization, and postoperative co-management. The choice of IOL — monofocal, toric, multifocal, or extended depth-of-focus (EDOF) — is one of the most consequential decisions in the surgical planning process.

Cataract affects approximately 95 million people worldwide and is responsible for approximately 51% of global blindness. In the United States, more than 4 million cataract surgeries are performed annually, making it the most frequently performed surgical procedure. Prevalence increases sharply with age — approximately 50% of adults over 75 have visually significant cataract. Posterior subcapsular cataract (PSC) is the most visually disabling morphology at an equivalent density due to its central, axial location.

The crystalline lens is an avascular, metabolically active structure dependent on the aqueous humor for nutrition. Age-related cataract results from progressive oxidative damage to lens proteins (crystallins), causing protein aggregation, loss of transparency, and increased light scattering. Nuclear cataract: hardening and yellowing of the lens nucleus — causes a myopic shift ("second sight") as the refractive index of the nucleus increases. Cortical cataract: spoke-like opacities in the lens cortex — caused by hydration and electrolyte imbalance. PSC: opacity at the posterior pole of the lens — associated with corticosteroid use, diabetes, uveitis, and radiation; disproportionately affects near vision and causes glare.

Gradual, painless reduction in visual acuity. Glare and halos (particularly PSC — worse in bright light and with oncoming headlights). Monocular diplopia. Myopic shift (nuclear cataract — patient may temporarily read without reading glasses: "second sight"). Reduced contrast sensitivity. Slit-lamp examination: nuclear opalescence graded by LOCS III (Lens Opacities Classification System III); cortical spokes; PSC opacity at the posterior pole best seen with retroillumination.

Surgical: phacoemulsification with IOL implantation is the definitive treatment. Surgical timing: when cataract-related visual impairment affects the patient's activities of daily living and quality of life — not based on a specific Snellen acuity threshold. IOL selection: monofocal (distance or near focus — most predictable); toric monofocal (corrects astigmatism); multifocal (simultaneous distance and near — increased spectacle independence but halos/glare); EDOF (extended range of focus — intermediate and distance with reduced dysphotopsia compared to multifocal); light-adjustable lens (LAL — postoperative UV adjustment). Preoperative biometry (IOLMaster, Lenstar) with modern formulas (Barrett Universal II, Kane, Hill-RBF) for IOL power calculation. Ocular surface optimization before surgery (see dedicated entry).

Annual dilated examination for visually significant cataract. Document BCVA, glare testing, and patient-reported functional impairment to support surgical referral. Postoperative co-management: day 1, week 1, month 1 visits — monitor for PCO, CME, IOP elevation, and wound integrity.