Cataract : Risk factors, Clinical Features, Management

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The word “Cataract” is actually derived from Latin word “Cataracta”, which implicate waterfall. The vision like looking through waterfall denotes trouble of cataract. Cataract is a vision disorder due to cloudiness, blurriness and lens opacity.

According to the world health Organization (WHO),

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“cataract is the lead cause of blindness in the world ( prevent blindness America, 2008 ).”

Cataract can develop in one or both eyes at any age as a result of a variety of causes. Cigarette smoking, long term use of corticosteroids especially at high dose, direct sunlight and ionizing radiation, diabetes, obesity,  and eye injuries an increase the risk of developing cataracts. The three most common types of senile (age-related) cataracts are defined by their location in the lens: nuclear, cortical and posterior subscapular. The extent of the visual impairment depends on their size, density and location in the lens. More than one type can be present in one eye.

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A nuclear cataract is caused by central opacity in the lens and has a substantial genetic component. It is associated with myopia (near-sightedness) which gets worse as the cataract progresses. If dense, the cataract severely blurs vision. Periodic changes in the prescription eyeglasses helps to manage this condition.

A cortical cataract involves the anterior, posterior or equatorial cortex of lens. Posterior subscapular cataracts occur in front of the posterior capsule. This type usually develops in younger people and sometimes associated with prolonged corticosteroid use, diabetes or ocular trauma.

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Risk factors for cataract formation

Aging

  • Loss of lens transparency
  • Clumping or aggregation of lens protein (( which leads to light scattering)
  • Accumulation of a yellow -brown pigment due to the breakdown of lens protein
  • Decreased oxygen uptake
  • Increase in sodium and calcium
  • Decrease in levels of vitamin C, protein and glutathione (an antioxidant)

Associated ocular conditions

  • Retinitis pigmentosa
  • Myopia
  • Retinal detachment and retinal surgery
  • Infection  (herpes zoster, uveitis)

Toxic factors

  • Corticosteroid especially at high doses and long term use
  • Alkaline chemical eye burns, poisoning
  • Cigarette smoking
  • Calcium, copper, iron, gold, silver and mercury which tend to deposit in the pupillary area pf the lens

Nutritional factors

  • Reduced levels of antioxidant
  • Poor nutrition
  • Obesity

Physical factors

  • Dehydration associated with chronic diarrhoea, use of purgatives in anorexia nervosa and use of hyperbaric oxygenation
  • Blunt trauma, perforation of the lens with sharp objects or foreign body, electric shock
  • Ultraviolet radiation in sunlight and x-ray.

Systemic diseases and  syndromes

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  • Diabetes mellitus
  • Down syndrome
  • Disorders related to lipid metabolism
  • Renal disorders
  • Musculoskeletal disorders

Clinical features of Cataract:

  • It is characterised by painless and blurry vision.
  • Perception that surroundings are dimmer (as of glasses need to clean)
  • Light scattering; reduced contrast sensitivity, sensitivity to glare and reduced visual acuity
  • Other effects include myopic shift (return of ability to do close work for [e.g. reading a fine print] without eyeglasses)
  • Astigmatism
  • Monocular diplopia (double vision)
  • Colour shift ( the aging lens becomes progressively more absorbent at the blue end of spectrum)
  • Brunescens (colour values shift to yellow-brown)
  • Reduced light transmission

Diagnostic assessment

  • Degree of  visual acuity is directly proportionate to density of the cataract
  • Snellen visual acuity test
  • Ophthalmoscopy
  • Silt-lamp bio microscopic examination.  

Management

Medical management

No non surgical ( such as medications, eye drops, eye eyeglasses)  treatment cures cataracts or prevents age-related cataracts. Studies have found no benefits from antioxidant supplements, vitamin C and E, beta carotene and selenium. Glasses or contact lenses, bifocal or magnifying lenses may improve vision. Mydriatrics can be used for short terms but glare is increased.

Surgical management

Generally, if reduced vision from cataract does not interfere with normal activities, surgery may not be needed. Surgery is performed on an outpatient basis and usually takes less than one hour, with patient being discharged within 30minutes as per the condition. Restoration of visual function through a safe and minimally invasive procedure is surgical goal, which is achieved with advances in topical anaesthesia, smaller wound incision (clear cornea incision), lens design (foldable and more accurate intra ocular lens measurement)

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When both eyes have cataracts, one eye is treated  first, with at least several weeks,, preferably months separating the two procedures. The delay also provides time for the first eye to recover, if there are any complications, the surgeon may decide to perform the second procedure differently.

The surgical options include

Phacoemulsification

In this method of extrascapular cataract surgery, a portion of the anterior capsule is removed, allowing extraction of the lens nucleus and cortex while the posterior capsule and zonular support are left intact. An ultrasonic device is used to liquefy the nucleus and cortex, which are then suctioned out through a tube. With increasing frequency, self healing  (sutureless) clear corneal incisions in the temporal part of the cornea are performed with Phacoemulsification, minimising post operative Astigmatism and thus decreasing bleeding and subconjuctival haemorrhage while speeding recovery of visual acuity.

Lens replacement

After the removal of the crystalline lens, the patient is referred as without lens. The lens which focuses light in retina must ne replaced for the patient to see clearly. There are three types of lens replacement options: aphakic eyeglasses, contact lenses and IOL implants.

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Aphakic glasses, although effective but are rarely used.  Objects are magnified by 25%, making them appear closer than they actually are. This magnification creates distortion.

Contact lenses provide patients with almost normal vision but because contact lenses need to be removed frequently, the patient also will need aphakic glasses. It is not advised for patients who have difficulty inserting, removing and cleaning them. Frequent handling and improper disinfection increases risk of infection.

IOL is the most common single-focus lens or monofocal IOL. Eyeglasses are still needed for distant or close vision because the single-focus lens, unlike natural lens of the eye cannot alter its shape to bring objects at different distances into focus. Insertion of IOLs during cataract surgery is the usual approach to lens replacement. A combined surgical approach using customised IOLs and refractive surgery for a customised vision correction is now proving beneficial for elderly patients (Fine, Hoffman & Packer, 2007).

 

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