Cataracts are the most common cause of blindness worldwide, affecting 16 million people globally. In the UK, advancing age is the most common cause, with one in three people over the age of 65 years affected.
Cataracts can be congenital, traumatic or secondary to ocular or systemic disease (see box, page 32).
Childhood cataract can lead to failed development of visual pathways. Timely surgery may reduce the risk of permanent visual impairment or blindness. The most common cause of congenital cataract is infection in utero.
Retinopathy of prematurity predisposes to later cataract formation, while older children on long-term corticosteroid therapy (topical, inhaled or oral routes) are also at risk.
In congenital cataract, red reflexes may be absent at routine 24-hour and six-week baby checks and parents may report that an infant is not smiling or following moving objects.
Older children describe blurred vision or glare in bright light; pupils may appear white or grey, and there may be a squint or nystagmus dating back to infancy.
Age-related cataract typically presents with gradual onset of painless visual disturbance. As the cataract alters the converging power of the lens, patients describe frequent changes of spectacles, or long-sighted individuals become able to read without spectacles.
|Causes of cataract|
Cataracts are visible as dark defects which may partially or completely obscure the red reflex. The lens may appear white or brown and visual acuity is reduced on testing. Patients may present with some of the following symptoms:
- Blurred vision
- Loss of contrast
- Faded colour perception
- Difficulty recognising faces or reading car number plates
- Glare - dazzled by headlights and sunlight
- Poor vision in bright light
- Monocular diplopia
- Fixed spots or haloes around bright lights
Differential diagnosis includes other causes of painless visual disturbance including refractive error, age-related macular degeneration, diabetic retinopathy, open-angle glaucoma and retinal detachment.
Conservative measures include anti-glare sunglasses, magnifying lenses or new prescription spectacles, and optometry should be repeated annually.
There is no specific level of visual loss that triggers referral for surgery. However, there should be a significant degree of visual impairment which impacts on lifestyle (such as difficulty reading or driving).
A decision to operate can safely be deferred if the patient chooses to wait, although there is no clinical reason to delay surgery while cataracts mature.
Surgery is indicated at any age and may benefit a patient's general health, reducing the risk of falls or enabling patients with diabetes to undergo retinopathy screening. The most recent visual acuity test should be included with the referral.
Mental capacity should be considered, when relevant, because patients must be able to lie still during surgery and co-operate with examinations and post-operative treatments. BP control should be optimised before surgery, and warfarin therapy stabilised.
In the UK, 200,000 cataract extractions are performed annually. Day-case surgery and the use of local anaesthetic agents (topical or intraocular injection) are the norm.
Phacoemulsification with extracapsular cataract extraction is the standard technique, using ultrasound to liquefy the lens which is then aspirated via a small incision in the sclera. An artificial silicone or acrylic lens is then introduced into the empty lens capsule in this suture-free procedure.
Bilateral cataracts are usually extracted on separate occasions to reduce the risk of blindness from bilateral endophthalmitis. Surgery on the second eye improves binocular vision, enhancing driving performance.
Most NHS patients receive monofocal lenses which are focused at a fixed distance. Multifocal and accommodating lenses can reduce the need for spectacles but may be associated with additional visual disturbances; however, lens technology is rapidly evolving.
Cataract (centre) in the eye of a 50-year-old man, which was caused by a childhood injury (Photograph: SPL)
4. Prognosis and complications
Vision should improve within days of surgery and patients can resume normal activities, avoiding swimming and racquet sports for the first week (because of the risk of eye trauma).
Topical antibiotics and steroids are required for several weeks and uncomplicated cases are reviewed one to three weeks postoperatively. Deteriorating vision, significant pain or redness in the eye warrant urgent specialist review.
Most patients will require spectacles, with optometry assessment deferred until four to six weeks after surgery when refraction has stabilised.
Surgical outcomes are good with low complication rates and 95 per cent of healthy eyes achieve 6/12 corrected vision. Complication rates are higher in patients with existing ocular disease or diabetes mellitus, and those taking anticoagulant therapy and alpha-antagonists, particularly tamsulosin.
Complications of surgery include posterior capsular opacification, glaucoma, uveitis, retinal detachment, macular degeneration, astigmatism and endophthalmitis.
Posterior capsular opacification is a common complication, presenting months after surgery with cloudy vision. YAG laser capsulotomy forms a hole in the opacified capsule, allowing light through. Complications are rare but include retinal detachment and lens displacement.
Patients may resume driving when they can read a number plate at 20.5 metres. If there are any concerns, they should be advised to contact the DVLA or their ophthalmologist for clarification about fitness to drive.
- Dr Duckworth is a salaried GP in Cornwall
References1. NICE. Implantation of accommodating intraocular lenses during cataract surgery. IPG209. London, NICE, February 2007.
2. NICE. Implantation of multifocal (non-accommodative) intraocular lenses during cataract surgery.IPG264. London, NICE, June 2008.
3. The Royal College of Ophthalmologists Cataract Surgery Guidelines. September 2010.