Diabetes-related cataract

Overview

•Hyperglycaemia saturates the polyol pathway → aldose reductase converts excess glucose to sorbitol → sorbitol accumulates in lens (cannot diffuse out) → osmotic water influx → crystallin protein disruption → lens opacity

•Advanced glycation end-products (AGEs) cross-link crystallins; oxidative stress compounds damage

•Transient myopic shift - acute hyperglycaemia causes osmotic lens swelling → increased refractive power → temporary short-sightedness; resolves with glycaemic control

⚠️

Refraction should only be measured once glucose is well controlled - a myopic shift in a diabetic patient should prompt HbA1c check before prescribing new glasses.

Presentation

•Gradual, painless reduction in visual acuity - pain suggests another diagnosis

•Glare - bright sunlight or night driving (oncoming headlights); often an early dominant symptom

•Blurred vision, haloes around lights, colour changes (yellowing/browning)

•Transient myopic shift with poor glycaemic control

•Examination: reduced or absent red reflex; grey/white/cloudy lens on direct illumination

Investigations

🥇 First-line

•visual acuity (Snellen chart) - establishes degree of impairment

•direct ophthalmoscopy - reduced/absent red reflex

•HbA1c and blood glucose - assess glycaemic control; defer surgery if unstable

🏆 Gold standard

•slit-lamp biomicroscopy - directly visualises cataract, determines morphology and extent

🥈 Second-line

•dilated fundal examination - essential to exclude co-existing diabetic retinopathy or maculopathy before surgery

Management

•Optimise glycaemic control - stabilise HbA1c before surgical referral; unstable diabetes increases post-operative risk and complicates surgical planning

•Optical optimisation - stronger spectacle correction or increased ambient lighting while awaiting surgery; not curative

•Definitive (only curative): phacoemulsification with intraocular lens (IOL) implant - day case, local anaesthesia; ultrasonic probe breaks up lens, aspirated and replaced with artificial IOL

•Pre-operative dilated fundal examination mandatory in diabetic patients - identify and treat significant retinopathy or maculopathy before surgery

💡

Cataract surgery can worsen diabetic macular oedema post-operatively. If significant maculopathy is present, treat (e.g. intravitreal anti-VEGF) before or around the time of surgery. NICE states surgery should not be rationed on visual acuity alone - functional impact and quality of life guide the decision.

Complications

•Posterior capsule opacification (PCO) - most common post-operative complication ('secondary cataract'); treated with Nd:YAG laser capsulotomy

•Worsening diabetic macular oedema - surgical inflammation promotes leakage from fragile diabetic vessels

•Endophthalmitis - rare but serious post-operative intraocular infection; painful red eye, visual loss, hypopyon; requires urgent intravitreal antibiotics

•Retinal detachment, posterior capsule rupture (intraoperative)