Cataract

Opacification of the crystalline lens of the eye, representing the leading cause of reversible visual impairment worldwide.

It is most commonly age related in aetiology, though it also arises from congenital causes (addressed with specific relevance to the risk of amblyopia if not promptly identified and treated), trauma, certain medications (particularly prolonged corticosteroid use), and specific metabolic conditions (including diabetes). Less commonly, it is secondary to intraocular inflammation or previous ocular surgery.

Cataract surgery is one of the most commonly performed and highly effective surgical procedures in contemporary medical practice. It generally produces substantial, durable visual improvement in appropriately selected patients.

Pathophysiology and classification

• Age related cataract is the commonest cause overall. It reflects progressive, cumulative oxidative damage and protein aggregation within the lens fibres over the course of life, producing progressive lens opacification.
• The pattern is classified by the predominant location of opacity within the lens: nuclear sclerotic, cortical, or posterior subcapsular. Each has somewhat differing characteristic visual symptoms and rate of progression.
• Congenital cataract, present at birth or developing in early infancy, carries particular importance given the risk of irreversible amblyopia.
• Visual deprivation from the opacified lens must be promptly identified and surgically addressed within the critical period of early visual development.
• Significant, visually obstructing congenital cataract is a time-sensitive paediatric ophthalmological emergency.
• Risk factors for accelerated cataract development or progression include diabetes, prolonged corticosteroid use (whether systemic or, particularly relevant, topical ocular corticosteroid use), significant ultraviolet light exposure, smoking, and previous ocular trauma or surgery.
• These associations are relevant to risk counselling and, in some cases, modifiable prevention strategies.

• The characteristic, gradually progressive symptom pattern is progressive, painless blurring of vision, typically affecting both distance and near vision to varying degrees according to the type and location of the cataract.
• Glare is common, and particularly problematic with bright light or oncoming headlights while driving at night.
• Contrast sensitivity is reduced.
• In some patients there is a perceived change in colour perception, with colours appearing more muted or yellowed.
• Nuclear sclerotic cataract characteristically produces a gradual myopic shift.
• Some patients, particularly those who previously required reading glasses, experience a temporary, paradoxical improvement in near vision as the lens becomes progressively more myopic, sometimes termed "second sight". Overall visual deterioration follows as the cataract advances further.
• Posterior subcapsular cataract characteristically produces disproportionate difficulty with glare and near vision, given its location directly in the visual axis.
• On examination, a visible lens opacity may be apparent on direct inspection with a pen torch or, more definitively, on slit lamp examination.
• The red reflex is characteristically reduced, dulled, or absent in the presence of significant cataract. This is a valuable screening finding.
• It is particularly critical in the assessment of infants: absence of a normal, symmetrical red reflex warrants urgent ophthalmological referral, given the possibility of congenital cataract or other serious causes of leukocoria, including retinoblastoma.
• Congenital cataract in infants may present with a visible white or grey pupillary opacity (leukocoria), poor visual fixation and tracking, nystagmus (reflecting poor visual development), or strabismus, with any of these findings warranting urgent, prompt ophthalmological assessment given the critical, time-sensitive relevance to preventing amblyopia.

• Diagnosis is established through slit lamp examination, allowing direct visualisation and characterisation of the type, location, and severity of lens opacity.
• Formal visual acuity assessment quantifies the functional impact of the cataract and supports the decision on the appropriate timing for surgical intervention.
• Full assessment of the remainder of the eye is an important component of preoperative evaluation. It includes the retina where visualisation permits, and any other coexisting ocular pathology that might independently limit visual potential following cataract surgery.
• It is directly relevant to appropriate patient counselling about the anticipated postoperative visual outcome.
• Biometric measurement of the eye (axial length and corneal curvature) is performed before surgery to calculate the appropriate power of the intraocular lens implant to be inserted at the time of cataract surgery, essential for achieving the desired postoperative refractive outcome.
• Any infant with suspected leukocoria or an abnormal red reflex requires urgent ophthalmological referral for full assessment.
• The referral is critical to prevent amblyopia in confirmed congenital cataract, and essential to exclude retinoblastoma, a serious, potentially life-threatening alternative cause of this same clinical sign.

• Cataract surgery is the standard, highly effective and, in contemporary practice, generally very safe treatment for visually significant cataract, typically performed under local anaesthesia as a day case procedure.
• It is typically performed as phacoemulsification (ultrasonic fragmentation and aspiration of the opacified lens material through a small corneal incision) with insertion of an artificial intraocular lens implant to replace the natural lens' focusing function.
• The timing of cataract surgery is generally guided by the degree of visual impairment and its functional impact on the individual patient's daily activities and quality of life, rather than any specific, fixed visual acuity threshold.
• This reflects a patient-centred approach to timing this generally elective, though highly beneficial, procedure.
• Preoperative counselling supports informed patient decision making on the choice of intraocular lens, an individually tailored aspect of surgical planning.
• Standard monofocal lenses provide clear focus at a single distance, typically selected for distance vision with reading glasses used for near tasks.
• Premium multifocal or extended depth of focus lenses offer the potential for reduced spectacle dependence across a range of distances. Recognised trade-offs include a higher likelihood of visual disturbances such as glare or halos, particularly at night.
• Congenital cataract requires urgent surgical management, given the critical, time-sensitive relevance to visual development during this critical period.
• Surgery is generally within the first few weeks of life for significant, visually obstructing bilateral cataract.
• Unilateral congenital cataract carries a particularly high risk of amblyopia even with prompt surgical treatment, given the strong competing visual input from the unaffected eye.
• It requires intensive, structured postoperative amblyopia management, including optical correction and patching therapy, addressed under amblyopia.
• Postoperative care following adult cataract surgery typically includes a course of topical antibiotic and anti-inflammatory (corticosteroid) eye drops over several weeks.
• Monitor for the recognised complications of this procedure.
• Posterior capsule opacification is a common, generally straightforward to treat late complication. It reflects proliferation of residual lens epithelial cells on the posterior lens capsule, and is managed effectively with a simple, outpatient laser capsulotomy procedure where it causes significant visual symptoms.
• Endophthalmitis is a less common, serious, sight-threatening postoperative infection requiring urgent recognition and aggressive treatment. It is addressed with the general principles applicable to any significant postoperative surgical site infection, combined with the specific, urgent ophthalmological management this complication requires.
• Regular postoperative follow up confirming satisfactory visual recovery and monitoring for the specific complications underpins full management of this generally highly successful, commonly performed procedure.