OP8.1-6 | Lens, Cataract and Aphakia — Practice Quiz

Correct. The lens is an avascular structure and depends entirely on the aqueous humour for nutrients (glucose, amino acids) and removal of metabolic waste.

The lens is avascular and devoid of nerve supply; it is nourished entirely by aqueous humour via diffusion and active transport through the lens epithelium.

The lens is avascular — it has no blood vessels and no nerve supply. The hyaloid artery, present only in fetal life, regresses before birth. The sole nutritional source in adults is the aqueous humour.

Correct. A crescentic iris shadow on the lens with oblique pen-torch illumination indicates an immature cataract — the anterior cortex is still partially clear, allowing the shadow of the iris to be cast on the opacity behind it.

The iris shadow test: a crescentic shadow = immature cataract (anterior cortex still clear, lens still partially transparent). No shadow = mature cataract (lens fully opaque, no translucency to cast a shadow).

The iris shadow test is decisive. Crescentic shadow = immature cataract (some anterior cortex clarity remains). No shadow = mature cataract (entire lens is opaque). This patient has an immature cataract.

Correct. PCO is the commonest late complication after ECCE. Residual lens epithelial cells proliferate on the posterior capsule, causing secondary visual loss. Treatment is Nd:YAG laser posterior capsulotomy.

PCO (posterior capsule opacification) — caused by proliferation and migration of residual lens epithelial cells onto the posterior capsule — is the commonest late complication of ECCE. It is treated by Nd:YAG laser capsulotomy, NOT repeat surgery.

PCO (posterior capsule opacification) is the commonest late complication of ECCE, occurring in up to 50% of patients within 5 years. The definitive treatment is Nd:YAG laser capsulotomy — not repeat surgery.

Correct. Iridodonesis is caused by loss of posterior support for the iris — seen in aphakia (lens absent) or lens subluxation (zonular weakness). The iris trembles with eye movement because its posterior contact is lost.

Iridodonesis (tremulousness of the iris on eye movement) is the hallmark bedside sign of aphakia or lens subluxation. Loss of the lens removes its posterior mechanical support, allowing the iris to tremble freely.

Iridodonesis is the classic sign of aphakia or lens subluxation. The crystalline lens normally provides posterior support to the iris. When the lens is absent or subluxated, the iris trembles on voluntary eye movement.

Correct. Retrobulbar block deposits local anaesthetic within the muscle cone, providing the most reliable akinesia and anaesthesia — essential for ECCE with its large limbal incision.

Retrobulbar block (injection behind the globe within the muscle cone) provides complete akinesia and anaesthesia. It is preferred for ECCE because the large incision (10-12 mm) demands a still eye. Topical anaesthesia provides analgesia only, with no akinesia.

For ECCE, which requires a 10-12 mm incision, complete akinesia is essential. Retrobulbar block (intra-conal injection) provides the best akinesia. Topical anaesthesia gives analgesia without akinesia and is suited only to phacoemulsification.

Correct. Phacomorphic glaucoma is a lens-induced secondary angle-closure. The swollen intumescent lens shallows the anterior chamber and closes the angle, causing acute elevation of IOP with pain and a shallow anterior chamber.

Phacomorphic glaucoma occurs when an intumescent (swollen) lens pushes the iris forward, shallowing the anterior chamber and closing the drainage angle. This is a lens-induced secondary angle-closure glaucoma — an emergency requiring urgent cataract extraction.

The combination of severe pain, raised IOP, and shallow anterior chamber points to angle-closure. In a mature cataract patient, the swollen lens (phacomorphic) is the cause — it physically shallows the anterior chamber and closes the drainage angle.

Correct. IOL power is calculated from axial length (A-scan ultrasound) and corneal curvature (keratometry) using formulae such as SRK II or SRK/T. Both measurements are mandatory preoperatively.

IOL power is calculated using the SRK/T formula (or similar): P = A constant - 2.5L - 0.9K, where L = axial length and K = average keratometry (corneal curvature). Keratometry and A-scan biometry are therefore the two essential preoperative measurements.

IOL power calculation requires two measurements: axial length (by A-scan biometry) and corneal curvature (by keratometry). These are combined in standard formulae (SRK II, SRK/T) to determine the required IOL power.

Correct. Aphakic spectacles magnify images by ~25-30%. In unilateral aphakia this causes intractable aniseikonia and binocular diplopia — the two retinal images differ so greatly in size that fusion is impossible. Spectacle correction is therefore contraindicated in unilateral aphakia.

Aphakic spectacles (+10D) magnify the retinal image by approximately 25-30%. In unilateral aphakia, this causes severe aniseikonia between the two eyes — the brain cannot fuse images of such disparate sizes, resulting in diplopia. Contact lenses (~7% magnification) or IOL implantation are therefore preferred.

Aphakic spectacles (+10D convex) magnify the retinal image by 25-30%. In unilateral aphakia this causes severe aniseikonia — image size disparity between the two eyes — making binocular fusion impossible (diplopia). Spectacles are therefore contraindicated; contact lenses or IOL implantation are preferred.

Correct. Phacoemulsification uses a 2-3 mm self-sealing corneal incision, requires no sutures in most cases, and allows same-day or next-day discharge. It is the current global standard for cataract surgery in well-resourced settings.

Phacoemulsification uses ultrasonic energy to emulsify the lens nucleus through a 2-3 mm self-sealing clear corneal incision. The small incision is sutured only if needed, allows rapid rehabilitation, and is the current global standard. MSICS uses a 5-7 mm scleral tunnel; ECCE uses 10-12 mm.

The 2-3 mm self-sealing sutureless incision is characteristic of phacoemulsification. MSICS uses a 5-7 mm scleral tunnel, ECCE uses a 10-12 mm limbal incision, and ICCE (now obsolete) uses an even larger incision.

Correct. The standard mydriasis protocol is tropicamide 1% (with or without phenylephrine) instilled every 15 minutes from 60 minutes before surgery, targeting a pupil diameter of 6-7 mm to facilitate safe nucleus delivery.

Preoperative mydriasis for cataract surgery: tropicamide 1% (with or without phenylephrine 5-10%) is instilled every 15 minutes starting 60 minutes before surgery, aiming for a pupil of at least 6-7 mm. Pilocarpine is a miotic — it would constrict, not dilate, the pupil.

Preoperative mydriasis for cataract surgery requires tropicamide 1% instilled every 15 minutes starting 60 minutes before surgery, targeting a dilated pupil of 6-7 mm. Pilocarpine is a miotic (causes constriction) and must never be used before cataract surgery.