A cataract is a clouding of the natural crystalline lens of the eye. The lens -- located just behind the iris and pupil -- is normally transparent, focusing light precisely onto the retina to produce a sharp image. When proteins within the lens aggregate and break down with age, they scatter incoming light rather than transmitting it clearly, producing the blurry, glary, and dim vision characteristic of cataracts.
Cataracts are the leading cause of correctable vision loss worldwide and affect the majority of people to some degree by the seventh decade of life. In Singapore, cataracts are extremely prevalent -- the ageing population, high rates of diabetes, and intense ultraviolet light exposure from the equatorial climate all accelerate lens opacity. The encouraging fact is that cataract surgery is one of the safest and most successful procedures in modern medicine, with an exceptionally high success rate and rapid visual recovery.
The crystalline lens is a transparent, biconvex structure approximately 10 mm in diameter, enclosed within a thin elastic capsule. It is composed primarily of specialised protein fibres called crystallins, arranged with extreme regularity to maintain optical clarity.
The lens serves two critical functions: it contributes approximately one-third of the eye's total focusing power (the cornea contributes the remaining two-thirds), and in younger eyes it changes shape to focus at different distances -- a process called accommodation. From the mid-40s onwards, the lens gradually loses this accommodating ability, producing presbyopia (the need for reading glasses). From the 50s and 60s onwards, protein aggregation begins to cause measurable opacity.
There are no blood vessels in the lens -- it relies on the aqueous humour (the fluid in the anterior chamber of the eye) for nutrition. This avascular environment means the lens is vulnerable to metabolic insults from elevated blood glucose (diabetes), free radical damage from UV radiation, and the cumulative effects of systemic medications including corticosteroids.
Cataracts are classified by the location of opacity within the lens. Each type has a characteristic visual symptom profile, rate of progression, and in some cases a specific set of associated risk factors. Many patients have more than one type simultaneously.
Nuclear cataracts develop gradually in the core of the crystalline lens. As the nucleus hardens and yellows with age, it progressively reduces optical clarity and shifts the lens towards greater refractive power. A characteristic early symptom is 'second sight' -- a temporary and paradoxical improvement in near vision as the lens becomes more myopic, occasionally allowing a patient who previously needed reading glasses to read without them. This improvement is short-lived; as the cataract matures, overall vision deteriorates. Nuclear cataracts are the most common type in Singapore's ageing population.
Cortical cataracts form in the cortex -- the outer layer of the lens surrounding the nucleus. They appear as white, wedge-shaped opacities radiating from the periphery toward the centre, resembling the spokes of a wheel. As they extend toward the optical axis, they scatter and split light, causing prominent glare, halos around lights, and difficulty driving at night. It is more common in individuals with diabetes, and often co-exists with nuclear cataract in older patients.
Posterior subcapsular cataracts develop on the back inner surface of the lens capsule, directly in the visual axis. Because of their central location, PSCs cause symptoms disproportionate to their size -- even a relatively small PSC significantly affects reading vision and causes intense glare and halos in bright light. PSC cataracts are associated with long-term corticosteroid use (oral, topical, or inhaled), diabetes, high myopia, and previous ocular trauma or inflammation. They tend to progress faster than nuclear or cortical cataracts and often require earlier surgical intervention.
Posterior polar cataracts are a congenital or early developmental form, present at birth or appearing in childhood. They sit at the posterior pole of the lens and are associated with a weakness or defect in the posterior lens capsule. This makes surgical removal technically demanding -- the risk of posterior capsule rupture during phacoemulsification is significantly higher than in other cataract types. Surgery should be performed by an experienced cataract surgeon familiar with posterior polar techniques, including the hydro-delineation approach. This distinction is particularly relevant when patients are choosing where to have their surgery.
Cataracts in Singapore are influenced by several factors that are more prominent than in Western populations:
These factors mean that Singaporean patients often present for cataract assessment earlier than Western counterparts, and that the ophthalmologist's consideration of associated conditions (myopia-related retinal pathology, diabetic retinopathy) alongside the cataract is particularly important at every assessment.
Cataract symptoms develop gradually and may not be noticed until the opacity has progressed significantly. The pattern of symptoms depends partly on the type of cataract:
The fundamental mechanism in age-related cataract is the denaturation and aggregation of lens crystallin proteins over decades. As these proteins clump together, they scatter rather than transmit light, producing opacity. This process is universal with ageing and cannot be prevented -- only slowed by limiting modifiable risk factors.
Cataract diagnosis requires examination by an ophthalmologist with a slit lamp -- a specialised microscope that illuminates and magnifies the structures of the anterior eye. Pre-surgical biometry provides the measurements needed to select the correct IOL power.
