Nuclear Cataract

Nuclear cataract is opacification and hardening (sclerosis) of the central lens nucleus. It is the commonest form of age related cataract.

• Mechanism: progressive compaction of old lens fibres, oxidation, and crystallin cross linking with chromophores, causing yellow brown colouration (brunescence) and increased refractive index.
• Risk factors: age, smoking, ultraviolet exposure, family history, and heavy alcohol use; high myopia and vitrectomy accelerate it.
• Grading: LOCS III nuclear opalescence (NO) and colour (NC) scales from 1 to 6; Emery-Little grades 1 to 4 for hardness.

• Gradual blurring of distance vision with myopic shift (index myopia), and temporary improvement of near vision without glasses ("second sight").
• Monocular diplopia or polyopia from irregular refractive index.
• Dulling and yellowing of colours, difficulty distinguishing blue and purple, reduced contrast sensitivity; relatively mild glare.
• Slit lamp: yellow to brown central nucleus; in brunescent or black cataract, the red reflex is lost and the nucleus is hard.
• Dense nuclear cataract can cause phacomorphic angle closure (swollen lens) in small eyes.

• Visual acuity with pinhole and refraction (myopic shift against stable previous prescriptions).
• Slit lamp grading, anterior chamber depth, pupil dilation, zonule check; gonioscopy if narrow angles.
• Fundus examination, macular optical coherence tomography.
• Preoperative planning: biometry, endothelial cell count (specular microscopy) for dense nuclei, which need more ultrasound energy.

• Early: updated spectacle correction, lighting, magnifiers, and monitoring.
• Surgical removal when visual function is reduced or when there is a medical indication:
  • Phacoemulsification with a nucleus fracture technique (divide and conquer, stop and chop, or phaco chop), and foldable intraocular lens, for most nuclei.
  • Dense (grade 4 to 5 and brunescent) nuclei: high viscosity dispersive and cohesive viscoelastic (soft shell technique) to protect the endothelium, lower flow rates, ultrasound torsional mode, or manual small incision cataract surgery or extracapsular extraction when nucleus is extremely hard or the endothelium is poor.
  • White or brunescent cataracts with poor view: stain the anterior capsule with trypan blue 0.06 percent, and perform capsulorhexis with care to avoid radial extension.
• Perioperative drops: preoperative NSAID, postoperative prednisolone acetate 1 percent four times daily tapered over 4 weeks, antibiotic for 1 week.
• Intracameral cefuroxime 1 mg in 0.1 mL at the end of surgery.
• Postoperative target refraction, plan for the second eye, and counselling about resolution of colour perception (patients may find colours bluer after surgery).