Lens and cataract surgery
Cataract surgery questions test the sequence of the operation, the optics of the implant, and the recognition of the two disasters of the first postoperative week: endophthalmitis and toxic anterior segment syndrome.
The lens and the cataract
The lens has capsule, epithelium, cortex and nucleus. Age-related nuclear sclerosis causes index myopia, cortical cataract causes glare, and posterior subcapsular cataract affects near vision and is typical of steroid use. Indications for surgery are visual complaints that affect the patient's life, not a fixed acuity threshold.
Biometry and implants
Measure axial length by optical biometry, keratometry and anterior chamber depth; select the formula by eye length and check the second eye. Target refraction is discussed preoperatively. Monofocal, toric, multifocal and extended-depth-of-focus implants trade spectacle independence against halos and contrast loss; multifocal implants need a healthy ocular surface and macula.
The operation and its complications
Phacoemulsification proceeds through incision, viscoelastic, continuous curvilinear capsulorrhexis, hydrodissection, nucleus division, cortex removal and in-the-bag implantation. Posterior capsule rupture with vitreous loss needs vitrectomy and a plan for the implant, usually sulcus or anterior chamber. Early complications include endophthalmitis (painful, hypopyon, days 2 to 7, tap and intravitreal antibiotics), toxic anterior segment syndrome (painless, day 1, sterile, diffuse oedema), wound leak and suprachoroidal haemorrhage. Late complications are posterior capsule opacification treated with Nd:YAG, retinal detachment, cystoid macular oedema and bullous keratopathy.
Worked example
One patient is painless on day 1 with diffuse limbus-to-limbus corneal oedema and a hypopyon; another is painful on day 4 with a hypopyon. Reasoning: early, painless and diffuse favours toxic anterior segment syndrome from retained viscoelastic or instrument residue, while day 4 with pain favours endophthalmitis, requiring a vitreous tap and intravitreal antibiotics. Timing and pain are the discriminators.
Traps
Ectopia lentis direction: Marfan superotemporal, homocystinuria inferonasal. Also operating without biometry checks in very long or short eyes, and missing pseudoexfoliation, which predicts zonular weakness.