[6] Cataract Flashcards
What is a cataract?
A clouding of the lens of the eye leading to decreased vision
How is lens transparency normally maintained?
By multiple factors including microscopic structure and chemistry
What are the 3 main parts of the lens?
- Capsule
- Epithelium
- Fibres
Describe the capsule of the lens
Elastic
What is the capsule of the lens made of?
Collagen
Where is the epithelium of the lens situated?
At the anterior portion between the capsule and fibres
What is the role of the epithelium of the lens?
It regulates the homeostasis and constantly lays down new fibres
What forms the bulk of the lens?
The fibres
What are the fibres of the lens?
Long, thin transparent cells arranged lengthwise from the posterior to anterior poles
How are the lens fibres organised?
In concentric layers
How does the lens fibre structure maintain transparency?
- Arrangement of fibres
- Lack of nuclei and other intracellular bodies
- Cytoskeletons retaining architecture
What can disruption of the lens fibres do?
Affect the integrity of the structure and lead to protein deposition
How do cataracts form?
From the deposition of aggregated proteins in the lens
What does protein aggregation in the lens do to vision?
- Clouding
- Light scattering
- Obstruction
What (other that protein aggregate deposition) contributes to the development of cataracts?
Accumulation of yellow-brown pigment in the lens that occurs with ageing
What aspects of vision are affected by the deposition of yellow-brown pigment in the lens?
- Colour vision
- Contrast
What can be made difficult as a result of the yellow-brown pigment deposition in the lens?
Reading
What are the causes of cataract?
- Age
- Trauma
- Metabolic disorders
- Medications
- Congenital problems
What are the main risk factors for cataract in the developed world?
- Age
- Smoking
- Diabetes mellitus
- Systemic corticosteroids
What are the risk factors for cataract in the developing world?
- Malnutrition
- Acute dehydrating diseases
- Cumulative exposure to sunlight
What are the less common risk factors for cataract?
- Female gender
- Uveitis
- UV exposure
- Poor nutrition
- Alcohol
- Inflammatory and metabolic eye diseases
What do the symptoms of cataract depend on?
The size, location and number of eyes affected by the opacity
What are the most common presenting symptoms of a patient with a cataract?
- Gradual, painless loss of vision
- Difficulty reading
- Failure to recognise faces
- Diplopia in one eye
- Haloes
How are most cataracts detected?
Noticed on a routine eye check before they are symptomatic
How can cataracts be described and categorised?
By the part of the lens that is affected
What are the three broad types of cataract?
- Nuclear sclerosis
- Cortical
- Posterior subcapsular
What forms a nuclear sclerosis cataract?
New layers of fibres added with ageing causing compression of the nucleus of the lens
What are the typical symptoms of nuclear sclerosis cataract?
- Gradually reduced contrast
- Reduced colour intensity
- Reading which may be surprisingly good for acuity level
- Difficulty recognising faces
What causes cortical cataract?
New fibres added to the outside which cause cortical spokes with age
When may cortical cataract not cause symptoms?
If the cataract is not on the visual axis or the entire cortex isn’t affected
What symptoms may present with a cortical cataract?
- Light scatter
- Problems with glare when driving at night
- Difficulty reading
- Daytime activity relatively unaffected
What is a posterior subcapsular cataract?
Opacity in the central posterior cortex
When do posterior subcapsular cataracts cause the most problem?
In good lighting
When are posterior subcapsular cataracts less trouble?
In low light levels when the pupil is dilated
What problems can be caused by a posterior subcapsular cataract?
- Difficulty in daytime driving
- Difficulty in reading
What may be seen on examination in cataract?
- Opacities seen as a defect in the red reflex
- Lens may appear brown or white under bright light
How is cataract diagnosed?
Clinically
What investigations can be done to rule out other causes when suspecting a cataract?
- Dilated fundus examination
- Measurement of intra-ocular pressure
- Glare vision test
- Slit lamp examination of the anterior chamber
What should be seen in examination of the fundus in cataract?
Normal (unless other pathologies)
What should be seen on measurement of intra-ocular pressure in cataract?
Normal (unless associated glaucoma)
What is seen on glare vision test in significant cataract?
Reduced visual acuity
What should be visible on slit lamp examination in cataract?
Cataract
What are the differentials for cataract?
- Macular degeneration
- Presbyopia
- Retinal disease
What is the only proven therapy for cataract?
Surgery
What is involved in modern cataract surgery?
Lens extraction and replacement
What is it called when a patient has a replacement lens?
Pseudophakia
What are the two types of procedures to remove the cataract lens?
Intracapsular and extracapsular
Which form of cataract removal is more commonly performed?
Extracapsular
When is surgery given in cataract?
No set threshold, consider risk of surgery against patient’s quality of life impact
What does extracapsular lens extraction involve?
Removal of the anterior capsule and extraction of the lens nucleus and cortex with the posterior capsule left to support the implanted lens
How can the lens be removed in extracapsular lens extraction?
- Via a large incision at the limbus
OR
- After phacoemulsification of the lens with ultrasound via a smaller incision
How are cataract surgeries performed in terms of anaesthetics?
Under local injection or anaesthetic eye-drops
How are cataract surgeries usually performed in terms of length of stay
Day-case
What post-operative care is required with cataract surgery?
Use of topical antibiotics and steroids and avoiding strenuous activity
What does intracapsular lens extraction involve?
Removing the entire lens and replacing with a plastic lens
What can cause poor visions after cataract surgery?
- Inadequate correction of refractive error post-op
- Failure to detect pre-existing eye conditions
- Surgical complications
What are the early surgical complications of cataract surgery?
- Posterior capsule rupture with or without loss of vitreous
- Protruding or broken sutures
- Trauma to iris
- Endophthalmitis
What is endophthalmitis?
A rare but devastating infection caused by Staph. epidermidis
In what percent of post-cataract surgery cases does endophthalmitis occur?
0.05-0.1%
What are the late complications of cataract surgery?
- Posterior capsule opacification
- Cystoid macular oedema
- Uveitis
- Retinal detachment
- Open or closed angle glaucoma
What percentage of post-cataract surgery cases does posterior capsule opacification occur in?
Around 40%
What advice should be given to patients with severe bilateral cataracts or failed extractions?
Not to drive and contact the DVLA
What are the potential complications of cataracts?
- Falling
- Depression
- Blindness
