Lamellar (Zonular) Cataract - PG Ophthalmology

THEORY QUESTION

Definition

Synonyms

• Zonular cataract (because it involves a zone/lamella of the lens)
• Perinuclear cataract

Aetiology / Causes

• Autosomal dominant (AD) - most common inherited form
• Can occur as an isolated finding

PG High-Yield: Lamellar cataract is classically associated with neonatal tetany due to hypocalcaemia (hypoparathyroidism). The lens zone being laid down at the time of the hypocalcaemic insult becomes opaque.

Morphology / Slit-Lamp Appearance

• Discrete disc-shaped opacity affecting a specific lamella of the lens
• The nucleus within is clear
• The cortex outside is clear
• "Riders" - radial extensions of opacity projecting outward from the equatorial edge of the opacity like spokes; these are pathognomonic of lamellar cataract
• Typically bilateral and symmetrical

Visual Significance

• Partially visually significant - the clear nucleus and clear outer cortex allow some vision
• Vision is typically worse in bright light (pupil constricts, the opacity now fills the pupillary aperture) - this is the "paradoxical pupil" phenomenon or photophobia
• Vision is better in dim light (pupil dilates, allowing light through the clear cortex peripherally)
• This behavior is characteristic and clinically important

Genetics

• AD inheritance - most common
• Can also be sporadic (isolated) or secondary to metabolic/systemic disorders
• Gene mutations involved: GJA3 (connexin 46), GJA8 (connexin 50), CRYAA, CRYGD

Differential Diagnosis of Lamellar Cataract Morphology

Management

• Bilateral dense cataracts: Surgery between 4-10 weeks of age to prevent deprivation amblyopia
• Bilateral partial (lamellar): May not require surgery urgently; monitor closely. Dilating drops (cyclopentolate/atropine) may help by dilating the pupil to allow vision through clear outer cortex
• Unilateral dense cataract: Surgery within first 6-10 weeks

• Lensectomy + anterior vitrectomy (in infants)
• Posterior capsulorhexis + vitrectomy (to prevent posterior capsular opacification, which is nearly universal if the posterior capsule is left intact)
• IOL implantation increasingly performed even in young children

• Aggressive amblyopia therapy (patching of the fellow eye)
• Optical rehabilitation: contact lenses preferred for unilateral aphakia in infants; spectacles for bilateral aphakia in older children

• Serum calcium, phosphorus, PTH
• Urine reducing substances (after milk feeding) - for galactosaemia
• Urine amino acid chromatography - for Lowe syndrome
• Fasting blood glucose
• TORCH screen (intrauterine infections)

CLINICAL CASE (PG Viva / Long Case Format)

• Visual acuity: 6/36 (right), 6/24 (left) by Snellen (age-appropriate testing)
• Convergent squint (esotropia) right eye
• Nystagmus absent
• Pupils: Equal, reactive; both equal in size
• Red reflex: Diminished bilaterally, with a central grey disc-shaped opacity visible
• Slit-lamp examination: Bilateral lens opacities - discrete, disc-shaped zones involving the perinuclear lamella, with clear nucleus centrally and clear cortex peripherally. Radial "rider" extensions noted at the equatorial margins (arrow-like projections). Opacity measures ~4.5 mm in each eye.
• Fundus: Normal (viewed indirectly through dilated pupil past the clear cortex)

Viva Questions and Model Answers

Bilateral lamellar cataract. The slit-lamp shows a discrete disc-shaped opacity in a specific lamella of the lens with clear nucleus inside and clear cortex outside, and the classic radial "rider" extensions at the equator. Bilateral symmetrical involvement, better vision in dim light (when the pupil dilates to expose clear cortex), and the history of neonatal convulsions (suggesting hypocalcaemia) all support this.

"Riders" - radial spoke-like extensions at the equatorial margin of the lamellar opacity.

The lens grows by adding new fiber layers (lamellae) around the nucleus throughout life. An insult (e.g., hypocalcaemia) affecting the lens epithelium during a specific developmental period causes opacity limited to the zone of fibers being laid down at that time. The period of insult determines which lamella is affected. Since the insult is transient, only the affected zone is opaque; earlier and later fibers (nucleus and outer cortex) remain clear.

The opacity is in a central/perinuclear lamella. In bright light, the pupil constricts and the opacity fills the entire pupillary aperture, blocking vision. In dim light, the pupil dilates, allowing light to pass through the clear cortex peripherally, improving vision. This is a characteristic feature of lamellar cataract and should prompt dilation drops as a temporizing measure.

• Serum calcium, phosphorus, PTH - to confirm hypocalcaemia/hypoparathyroidism
• Urine reducing substances after milk feeding - to exclude galactosaemia
• TORCH serology - to exclude intrauterine infection
• Urine amino acid chromatography - to exclude Lowe syndrome
• Fasting blood glucose
• Chromosome analysis if dysmorphic features present

• Partial bilateral lamellar cataracts may be monitored if vision is only mildly affected; mydriatics (atropine drops) help by dilating the pupil
• If visually significant (>3 mm opacity or VA significantly reduced): bilateral lensectomy + posterior capsulorhexis + anterior vitrectomy; IOL implantation considered (age-appropriate target refraction)
• Post-operative: aggressive amblyopia therapy (patching), optical correction (contact lenses/spectacles), and regular follow-up for glaucoma (up to 20% risk by 5 years post-surgery)
• Treat underlying metabolic cause (calcium supplementation for hypoparathyroidism)

• Posterior capsular opacification (near universal if posterior capsule retained) - hence posterior capsulorhexis + vitrectomy done primarily
• Secondary membrane formation across pupil
• Glaucoma (open-angle in up to 20% by 5 years; angle-closure early post-op due to pupillary block)
• Amblyopia (main long-term threat to vision)
• Retinal detachment (rare, late)
• Lens epithelial proliferation / Soemmering ring

Between 4 and 10 weeks of age. Surgery before 4 weeks risks higher glaucoma incidence; surgery after 10 weeks risks irreversible deprivation amblyopia.

Summary Box (High-Yield PG Points)