Cataract - Ophthalmology _ Fastbleep

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/ Biology Notes/ Ophthalmology

Cataract

Written by: Tay Xue Chao, Brian Diaz from Manchester University,

Introduction

A cat aract is opacity within the lens of the eye, and may affect either one or both eyes. The

opacity changes the transparency and refractive index of the lens, resulting in the blurring of a

persons vision. According to the World Health Organisation (WHO, 2007), cataracts account for

47.9% of blindness worldwide. The reported prevalence of childhood cataracts ranges from 1-15

per 10,000 children.
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Nuclear Cataract

Cortical Cataract

Subcapsular Cataract

This occurs at the centre of the lens, and

interferes with distance vision. It is the most

common type of cataract, and is usually the

result of advancing age.

This begins at the outer rim of the lens, and

gradually works towards the centre of the

lens. It resembles the spokes of a wheel. It is

most commonly found in patients with

diabetes.

This affects the back of the lens, causing

glare and blurring of vision. It is the most

rapidly progressing type of cataract. Risk

factors for the development of a

subcapsular cataract are use of steroids,

diabetes, and myopia.

Types of Cataract

Aetiology


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Risk Factors

The following are associated with acquired cataract in developed nations:

Age (above 60 years of age)

Smoking

Phys ical trauma

Alcohol consumption

Sunlight exposure

Low educational levels

Poor lifest yle habits inclusiv e of malnutrition and physic al inactiv ity

Metabolic sy ndrome

Diabetes mellitus

Sys temic cortic osteroid use and possibly prolonged administration of high doses ofinhaled corticosteroids

Pathogenesis

The lens of the eye is composed of specialised cells arranged in a highly ordered and complex


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manner. These cells are stratified epithelia and have a very high content of cytoplasmic protein

the crystallins. These proteins, along with the complex structure, impart transparency to the

lens.

Unlike other epithelia, the lens does not shed nonviable cells. As such, it is particularly

susceptible to the degenerative effects of aging on cell structure. The exact pathogenetic

mechanisms of this are not known. It has, however been observed that most of the risk factors

identified are environmental stressors that lead to the formation of toxins or the impairment ofantioxidants.

Clinical Presentation: Symptoms and Signs

Opacification of lens is painless, progressive, and highly variable

Often bilateral but asymmetrical

Common complaints inc lude problems with night driving, reading road signs, and

reading fine print

"Myopic s hift" (an increase in nearsightedness) happens prior to opacificati on of lens Cataracts may present as immature (transmits red reflex), mature (does not transmit

red reflex), or hypermature (cortex of lens has liquefied and lens nucleus is mobile within

capsule)

Mature and hypermature cataracts can give rise to secondary glaucoma that is

associated with a red and painful eye (unlike many other glaucoma's)

With regards to the presentation of congenital cataracts:

Approximately one-third of congenit al cat aracts in chil dren are inherited, one third are ass ociat ed

with systemic diseases, and one-third are idiopathic or sporadic.

Parent's observation of cataract

Visual behaviour that deviates from normal

Asy mmetry of red reflex identified on Bruckner testing (simultaneous red reflex tes t)

Leukocoria (white pupillary reflex)

Nystagmus

Strabismus (Squint)

Photophobia

Delayed development

Family history of hereditary cataracts

Genetic disorder assoc iated with cataracts

Cataracts detected in infants and young children must be referred to a specialist as soon

as possible in order to allow for normal visual development and to prevent blindness.

Differential Diagnosis

Macular degeneration

Presbyopia Retinal disease

Retinoblastoma (in children)

Diagnosis


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The slit lamp is a binocular

microscope

Provides a three dimensional view of

the eye

A beam or "slit " of light is used as

opposed to diffuse light

Height and width can be adjusted

Anatomic features of the eye can be

accentuated

Provides greater magnification and

illumination than most handheld devices

Is used to diagnose a number of

traumatic and non-traumatic disorders,

Slit lamp examination
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including cataract

Posterior capsular opacification on retroillumination with slit lamp

Prevention

There is no proven therapy to prevent either cataract formation or its progression once it

has developed. However, the following have been observed to be of benefit in decreasingrisk:

Eating a healthy diet

Eating a diet rich in lutein and zeaxanthin

Smoking cessation

Postmenopausal oestrogen use (longer than 10 years)

Vitamin supplementation

Management


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Most widely used

Most effective

Safest

The hard lens nucleus is liquefied by

an ultrasonic probe

Fragments are aspirated, along with

soft lens fibres

Replacement lens (folded) is placed

into empty capsular bag where it gradually

unfolds

The incision made through lens

capsule heals on its own

Phacoemulsion
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Early complications

Rupture of posterior capsule (3%)

Trauma to iris

Prolapsed iris

Wound gape

Haemorrhage in anterior chamber

Rupture of lens capsule with loss of

vitreous

Vit reous haemorrhage

Choroidal haemorrhage

Post-operative endophthalmitis

Late Complications

Opacification of posterior capsule(20%)

Cystoid macular oedema

Uveitis

Retinal detachment

Open and closed angle glaucoma

Age-related macular degeneration

Complications that may result from surgery

Postoperative thickening of the lens capsule frequently occurs over time causing gradual

deterioration of vision. This can be treated by splitting the capsule with a laser.

Prognosis

Postoperatively 95% of patients that have no other complications achieve a corrected acuity of

6/12.

The major risk factors that affect prognosis are diabetes and diabetic retinopathy. Diabetes

causes fluctuating blood glucose levels. Occasionally, high blood glucose levels cause

oedema and subsequent swelling of the lens. When the blood glucose diffuses, the swelling in

the lens also reduces. This repeated action causes cataracts.

In paediatric cataracts, visual acuities of 20/20 to 20/40 may be achieved if cataracts are

diagnosed and treated early.

Summary

Cataracts are lens opacities that can range in severity from unnoticed dots to total fogging of

vision. Cataracts are by far the commonest cause of preventable blindness worldwide.

Age-related causes are most common, although there are also familial or congenital caus es.

Gradual painless deterioration of vision is the most common symptom reported, with other

possible co-existing symptoms such as glare and problems with night driving dependent on the

type of cataract.

Early symptoms can be alleviated with spectacles, but to correct vision, surgery is required.

Surgery involves the insertion of an intraocular lens to replace the affected one. The exact

technique used is determined by the aetiology and density of the cataracts. Phacoemulsification

(a form of small incision surgery) is the most frequently used technique. Further investigations

such as blood glucose, serum calcium, and liver biochemistry should be considered in order to


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diagnose any possible underlying metabolic disorder.

It is also worth noting that cataracts may not always be bilateral, and hence, eyes may be

managed and treated individually according to the severity of the cataract within each eye.

Useful resources

Websites:

http://www.cataract-doctor.com/

Videos:

http://www.careflash.com/video/cataracts (http://www.careflash.com/video/cataracts) (Cataracts

explained in lay terms)

http://www.rootatlas.com/wordpress/video/866/cartoon-cataract-surgery-video/

(http://www.rootatlas.com/wordpress/video/866/cartoon-cataract-surgery-video/)

(Cataract surgery, Phacoemulsification) My favourite!

References

Kumar and Clark Clinical Medicine 7th edition

UpToDate articles "Cataract", "Cataract in children", and "Slit lamp examination"

http://www.patient.co.uk/doctor/Cataracts-and-Cataract-Surgery.htm

(http://www.patient.co.uk/doctor/Cataracts-and-Cataract-Surgery.htm)

All images tak en from: http://en.wikipedia.org/wiki/Cataract_surgery

(http://en.wikipedia.org/wiki/Cataract_surgery)

SkillsEye Examination & Vision AssessmentIdentifying and Treating Eye EmergeOcular History TakingUsing an OphthalmoscopeConditions

Age-related Macular DegenerationAllergic Eye Diseas esBlindness: Global EpidemiologyCataractCorneal DisordersCranial Nerve III, IV and VI PalsiesEyelid, Orbital and Lacrimal DisordersGlaucomaIntraocular TumoursOcular InflammationOphthalmic InfectionsOphthalmic Involvement in Systemic DiseaseRetinal DetachmentRetinitis PigmentosaRetinoblastomaRetinopathySquintPresentationsDiplopiaDry EyeEyelid Lumps, Bumps and Rashes

Floaters, Flashers and HalosForeign BodyLoss of VisionOcular Pain and HeadachesOphthalmic TraumaOptic Disc Swelling and Optic AtrophyOrbital Swellings
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