The Lens Flashcards
What the displacement of the lens from its physiological position called, and what may it be associated with?
Ectopia lentis (rare). May be associated with glaucoma.
The refractive complications may necessitate contact lens wear, or even lens removal. Paradoxically, the optical effects of partial dislocation are more disabling than complete dislocation.
What is the most frequently seen disorder of the lens?
Loss of clarity, termed “cataract”.
Almost everybody over the age of 70 has some degree of lenticular opacity, although many remain asymptomatic and relatively few require surgery.
Congenital and infantile cataract differ morphologically and aetiologically from age-related opacity.
What is the majority of cataract encountered in clinical practice associated with?
Senile cataract (‘normal’ age-related degenerative change).
Pathogenesis unknown, but UV light has been implicated.
Cataract presenting in young or early middle aged person should prompt further Ix.
Name 6 systemic disorders causing pre-senile cataract.
- Diabetes mellitus
- Corticosteroid Rx
- Atopy
- Galactosaemia
- Hypocalcaemia
- Dystrophia myotonica
Name 7 ocular disorders/exposures causing pre-senile cataract.
- Blunt or perforating trauma
- High myopia
- Recurrent uveitis
- Topical steroid use
- Ionising radiation
- UV light
- Infrared irradiation
What are some causes of infantile cataract, and what is the breakdown of cases due to these causes?
One third are inherited autosomal dominant.
Another third are caused by birth trauma or maternal infection during pregnancy (particularly rubella and toxoplasmosis).
Galactosaemia is the most common metabolic cause of congenital or infantile cataract. Wilson’s disease, Lowe’s syndrome and Fabry’s disease are rare causes.
Describe the three possible morphological variants of senile cataract (p. 48 for diagrams).
- Nuclear sclerosis: gradually deepening diffuse brunescence (brown)
- Subcapsular: shallow opacification just beneath the capsule, more commonly posterior than anterior
- Cortical: discrete spoke-like opacities of the cortex
Senile cataract takes the form of one or a combination of these.
How may disturbance of vision present in cataract? Name four ways.
- Gradual loss of clarity with dimness of vision
- Progressive myopia caused by increasing density of the nucleus (nuclear sclerosis)
- Glare
- Monocular diplopia
Symptoms may vary with changes in ambient illumination, as the pupil constricts and dilates. If cataract is predominantly uniocular, it may go unnoticed until the other eye becomes affected.
How does cataract present in children?
They do not complain of visual loss.
Detected either by routine examination, or by obvious leukocoria in family photographs.
The prognosis for visual recovery after surgery depends especially on what?
Retinal health. Hence, dilated fundal examination is mandatory.
If the retina cannot be seen, field of vision testing using a light or hand-waving, pupil testing for RAPD, and US (to exclude retinal detachment or tumour) should be performed.
If the retina cannot be adequately examined preoperatively, the prognosis is guarded until the postoperative period.
What are history and examination directed at when exploring cataract?
Determining the level of visual impairment, and detecting a cause.
Snellen visual acuity is always measured but correlates poorly with functional impairment.
A cataract can be detected by examination of the red reflex after pupil dilatation using the direct ophthalmoscope.
In children, cataract must be differentiated from other causes of leukocoria. Name 4 acquired causes and 3 hereditary causes of leukocoria.
Acquired: 1. Trauma* 2. Hypermature cataractous lens* (hypermature cataract) 3. Anterior intraocular tumour 4. Syphilis Hereditary: 1. Marfan's syndrome* (upward dislocation) 2. Homocystinuria 3. Weill-Marchesani syndrome
Examination under GA, US and electrophysiology may be required.
* = only three listed in page summary, assume main ones.
What are 3 management difficulties in children with cataract?
Simple removal of opacity does not restore vision, because:
- Need correction of aphakia
- Need management of amblyopia (likely to limit visual improvement, especially in unilateral cataract)
- Eye may still be growing, so that lens implantation is controversial.
Name 4 indications for cataract surgery:
- Visual impairment poor for individual
- Diabetic retinopathy (when cataract prevents adequate retinal examination, or photocoagulation/laser treatment)
- Lens-induced glaucoma
- Lens-induced uveitis
Name four principle considerations in cataract surgery:
- Choice of anaesthesia
- Incision: via cornea or anterior sclera
- Technique of cataract removal
- Correction of aphakia: by intraocular lens implantation, contact lens or aphakic spectacles.
