Q3 LONG ANSWER 10M ★ High-yield

Describe the techniques of cataract surgery with biometry and intraocular lenses.

Ophthalmology · 3rd Professional

Indications and Preparation

Indications for cataract surgery — visual, which is the usual one: the vision no longer meets the patient’s needs, and there is no fixed acuity threshold, since a driver or a surgeon needs more than a bedbound patient; medical, where the cataract itself threatens the eye — phacomorphic or phacolytic glaucoma, phacoantigenic uveitis, lens subluxation; diagnostic and therapeutic, where the lens prevents examination or treatment of the retina, as in diabetic retinopathy needing laser; and cosmetic in a blind eye with a white pupil
Anaesthesia — topical (proparacaine or lidocaine gel, with intracameral lidocaine), now used for most phacoemulsification; sub-TENON, safe and effective; peribulbar; retrobulbar, now largely abandoned because of its complications — globe perforation, retrobulbar haemorrhage, optic nerve injury and brainstem anaesthesia from inadvertent injection into the optic nerve sheath, which causes apnoea and requires resuscitation; and general anaesthesia for children, the uncooperative and the deaf

Surgical Techniques

Technique	Description, advantages and limitations
Intracapsular (ICCE)	The whole lens with its capsule is removed, using a cryoprobe after zonulolysis with alpha-chymotrypsin. Requires a large (160-degree) limbal section. Obsolete, because there is NO capsular support for a posterior chamber lens, and the vitreous is left in contact with the cornea — giving aphakic bullous keratopathy, cystoid macular oedema and retinal detachment. Retained only for a markedly subluxated or dislocated lens
Extracapsular (ECCE)	An anterior capsulotomy is made, the nucleus expressed whole and the cortex aspirated, leaving the posterior capsule intact to support an intraocular lens in the bag. Needs a 10 to 12 mm section with sutures, so there is more astigmatism and slower recovery. Superseded, but still valuable for a very hard nucleus
Manual small-incision cataract surgery (SICS)	The workhorse of high-volume Indian cataract surgery. A 6 to 7 mm self-sealing sclerocorneal tunnel is made, the nucleus prolapsed into the anterior chamber and delivered whole or in pieces, and an intraocular lens implanted. Requires NO sutures and NO expensive machine, is fast and cheap, and gives results comparable to phacoemulsification at a fraction of the cost. It is also safer than phaco for a very hard, brunescent or mature cataract.
Phacoemulsification	The nucleus is fragmented by an ultrasonic probe and aspirated through a 2.2 to 3 mm incision, and a foldable lens injected. Advantages: a small self-sealing wound, minimal astigmatism, a closed and stable chamber, and very rapid rehabilitation. Disadvantages: expensive equipment, a long learning curve, and greater difficulty with a hard nucleus, where the ultrasound energy may damage the corneal endothelium
Femtosecond laser-assisted (FLACS)	The laser performs the capsulotomy, nuclear fragmentation and incisions; greater precision but a substantially higher cost, and no clear outcome advantage

The steps of modern cataract surgery → incision — a self-sealing clear corneal or sclerocorneal tunnel, with a side-port for the second instrument → viscoelastic (ophthalmic viscosurgical device) to maintain the chamber and protect the endothelium → capsulorhexis — a continuous curvilinear capsulorhexis (CCC) of 5 to 5.5 mm, whose smooth continuous edge resists tearing and is what allows the whole of modern surgery.
It should be slightly smaller than the optic, so the capsule overlaps the lens edge through 360 degrees and suppresses after-cataract → hydrodissection — fluid injected beneath the capsule to separate the cortex from it; and hydrodelineation to separate nucleus from epinucleus → nucleus removal — by phacoemulsification (divide-and-conquer, stop-and-chop, or phaco-chop) or by prolapse and delivery in SICS → cortex aspiration by irrigation-aspiration, with careful capsular polishing to remove residual epithelial cells → intraocular lens implantation in the capsular bag → Removal of viscoelastic — which must be complete.

Biometry and Intraocular Lenses

Biometry determines the power of the lens to be implanted, and errors in it are the commonest cause of an unhappy patient after technically perfect surgery. It requires two measurements:
Axial length — by ultrasound, either applanation (which indents the cornea and therefore under-estimates the length, leading to a hypermetropic surprise) or immersion (more accurate); or by optical biometry (IOLMaster, Lenstar) using partial coherence interferometry, which is non-contact, more accurate and now the standard, though it fails in a dense cataract where ultrasound still succeeds. An error of 1 mm in axial length produces 2.5 to 3 dioptres of refractive error
Keratometry — the corneal curvature; an error of 1 dioptre in K gives 1 dioptre of error

Intraocular lens	Features
Material — PMMA	Rigid; requires an incision as large as the optic; cheap and used in ECCE and SICS
Material — hydrophobic acrylic	Foldable; the most widely used; low rate of after-cataract
Material — hydrophilic acrylic and silicone	Foldable; silicone is avoided where silicone oil may be used for retinal surgery.
Design — square-edged optic	The single most important design feature: a sharp posterior edge forms a mechanical barrier to migrating epithelial cells and markedly reduces after-cataract
Monofocal	The standard; gives excellent distance vision, and reading glasses are needed
Multifocal and extended depth OF focus	Provide spectacle independence at the cost of reduced contrast and glare and haloes; unsuitable where there is macular disease or high expectations of night driving
Toric	Corrects pre-existing corneal astigmatism; requires accurate axial alignment, and rotation of more than a few degrees loses the effect
Position	IN the bag is ideal; ciliary sulcus if the posterior capsule is torn; and anterior chamber, iris-fixated or scleral-fixated lenses where there is no capsular support

Choosing the Technique

Situation	Preferred technique and reason
Routine soft-to-moderate cataract, good facilities	Phacoemulsification — smallest wound, fastest recovery
Hard, brunescent or mature cataract	SICS — safer than phaco.
High-volume, resource-limited or camp-referred setting	SICS — no machine, no sutures, fast and cheap, with comparable outcomes
Very shallow anterior chamber or a compromised endothelium	SICS or careful phaco with a dispersive viscoelastic to protect the endothelium
Subluxated or dislocated lens	ICCE, or lensectomy with vitrectomy and a scleral- or iris-fixated lens
Paediatric cataract	Lensectomy with primary posterior capsulotomy and anterior vitrectomy
Uveitic cataract	Phaco or SICS in a quiet eye with steroid cover; a hydrophobic acrylic lens in the bag
Pseudoexfoliation with zonular weakness	Careful technique with a capsular tension ring; expect poor dilation and late lens dislocation

Applied Aspects

Get the biometry right; a perfect operation with a wrong lens power is a failure from the patient’s point of view, and refractive surprise is the commonest source of dissatisfaction
Use immersion or optical biometry rather than applanation; applanation indents the cornea, shortens the measured axial length and produces a hypermetropic result
Do not wait for a cataract to "ripen"; a hypermature lens is harder to remove, has weaker zonules and may present with phacolytic or phacomorphic glaucoma

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