Cataract

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Cataract is a clouding of the lens in the eye leading to a decrease in vision. It can affect one or both eyes. Often it develops slowly. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognizing faces. Poor vision may also result in an increased risk of falling and depression. Cataracts are the cause of half of blindness and 33% of visual impairment worldwide. Cataracts are most commonly due to aging, but may also occur due to trauma, radiation exposure, be present from birth, or occur following eye surgery for other problems.

Signs & Symptoms- Signs and symptoms vary depending on the type of cataract, though considerable overlap occurs. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Those with posterior subcapsular cataracts usually complain of glare as their major symptom. The severity of cataract formation, assuming no other eye disease is present, is judged primarily by a visual acuity test. The appropriateness of surgery depends on a patient’s particular functional and visual needs and other risk factors, all of which may vary widely.

Causes-

Age– Age is the most common cause. Lens proteins denature and degrade over time, and this process is accelerated by diseases such as diabetes mellitus and hypertension. Environmental factors, including toxins, radiation, and ultraviolet light, have cumulative effects, which are worsened by the loss of protective and restorative mechanisms due to alterations in gene expression and chemical processes within the eye.

Trauma- Blunt trauma causes swelling, thickening, and whitening of the lens fibers. While the swelling normally resolves with time, the white color may remain. In severe blunt trauma, or injuries which penetrate the eye, the capsule in which the lens sits can be damaged. This allows fluid from other parts of the eye to rapidly enter the lens leading to swelling and then whitening, obstructing light from reaching the retina at the back of the eye. Cataracts may develop in 0.7 to 8.0% of cases following electrical injuries.

Radiation- Ultraviolet light, specifically UVB, has been shown to cause cataracts, and some evidence indicates sunglasses worn at an early age can slow its development in later life. Microwave radiation has also been found to cause cataracts. The mechanism is unclear, but it may include changes in heat-sensitive enzymes that normally protect cell proteins in the lens. Another possible mechanism is direct damage to the lens from pressure waves induced in the aqueous humor. Cataracts have been associated with ionizing radiation such as X-rays. The addition of damage to the DNA of the lens cells has been considered. Finally, electric and heat injuries denature and whiten the lens as a result of direct protein coagulation. This same process makes the clear albumin of an egg become white and opaque after cooking. Cataracts of this type are often seen in glassblowers and furnace workers. Lasers of sufficient power output are known to damage the eyes and skin.

Genetics- The genetic component is strong in the development of cataracts, most commonly through mechanisms that protect and maintain the lens. The presence of cataracts in childhood or early life can occasionally be due to a particular syndrome. Examples of chromosome abnormalities associated with cataracts include deletion syndrome (part of chromosome gets deleted), cri-du-chat syndrome (rare genetic disorder due to missing part of chromosome), Down syndrome (presence of third copy of chromosome), Patau’s syndrome (chromosomal abnormality), trisomy 18 (Edward’s syndrome) and Turner’s syndrome (female misses all or part of X chromosome), and in the case of neurofibromatosis type 2 (an inherited disease), juvenile cataract on one or both sides may be noted. Examples of single-gene disorder include Alport’s syndrome, Conradi’s syndrome, myotonic dystrophy, and oculocerebrorenal syndrome or Lowe syndrome.

Skin Diseases- The skin and the lens have the same embryological origin and can be affected by similar diseases. Those with atopic dermatitis (inflammation of skin) and eczema occasionally develop shield ulcers cataracts. Ichthyosis (scaly skin) is an autosomal recessive disorder associated with cuneiform cataracts and nuclear sclerosis. Basal-cell nevus and pemphigus have similar associations.

Drug Use- Cigarette smoking & consumption of alcohol has been shown to double the rate of nuclear sclerotic cataracts and triple the rate of posterior subcapsular cataracts. Evidence is conflicting over the effect of alcohol. Some surveys have shown a link, but others which followed patients over longer terms have not.

Medications- Some drugs, such as corticosteroids (steroid hormones) can induce cataract development. People with schizophrenia (abnormal social disorder) often have risk factors for lens opacities (such as diabetes, hypertension, and poor nutrition) but antipsychotic medications (psychiatric medicines) are unlikely to contribute to cataract formation. Miotics (construction of excessive pupil) and triparanol may increase the risk.

Iatrogenic- Nearly every person who undergoes a vitrectomy — without ever having had cataract surgery — will experience progression of nuclear sclerosis at 6-months and 12-month after the operation. This may be because the native vitreous humor is significantly different from the solutions used to replace the vitreous (vitreous substitutes), such as BSS Plus. This may also be because the native vitreous humour contains ascorbic acid which helps neutralize oxidative damage to the lens and because traditional vitreous substitutes do not contain ascorbic acid. As such, for phakic patients requiring a vitrectomy it is becoming increasingly common for ophthalmologists to offer the vitrectomy with a combined prophylactic cataract surgeryprocedure to prophylactically prevent cataract formation.

Apart from these there are many factors or diseases which cause cataract such as-

  • Diabetes
  • Hypertension
  • Obesity
  • Prolonged use of corticosteroid medications
  • Medicines used to reduce cholesterol
  • Previous eye injury or inflammation
  • Previous eye surgery
  • Hormone replacement therapy
  • High myopia
  • Family history

Treatment- Cataract removal can be performed at any stage and no longer requires ripening of the lens. Surgery is usually ‘outpatient’ and performed using local anesthesia. Almost all patients can achieve all good vision  after surgery.

Phacoemulsification or Phaco is the most widely used cataract surgery. This procedure uses ultrasonic energy to emulsify the cataract lens. Phacoemulsification typically comprises six steps:

Anaesthetic – The eye is numbed with either a subtenon injection around the eye or using simple eye drops.

Corneal incision – Two cuts are made through the clear cornea to allow insertion of instruments into the eye.

Capsulorhexis – A needle or small pair of forceps is used to create a circular hole in the capsule in which the lens sits.

Phacoemulsification – A handheld probe is used to break up and emulsify the lens into liquid using the energy of ultrasound waves. The resulting ’emulsion’ is sucked away.

Irrigation and Aspiration – The cortex, which is the soft outer layer of the cataract, is aspirated or sucked away. Fluid removed is continually replaced with a saline solution to prevent collapse of the structure of the anterior chamber (the front part of the eye).

Lens insertion – A plastic, foldable lens is inserted into the capsular bag that formerly contained the natural lens. Some surgeons also inject an antibiotic into the eye to reduce the risk of infection. The final step is to inject salt water into the corneal wounds to cause the area to swell and seal the incision.

Extracapsular Cataract Extraction (ECCE) consists of removing the lens manually, but leaving the majority of the capsule intact. The lens is expressed through a 10- to 12-mm incision which is closed with sutures at the end of surgery. ECCE is less frequently performed than phacoemulsification, but can be useful when dealing with very hard cataracts or other situations where emulsification is problematic. Manual Small Incision Cataract Surgery (MSICS) has evolved from ECCE. In MSICS, the lens is removed through a self-sealing scleral tunnel wound in the sclera which, ideally, is watertight and does not require suturing. Although “small”, the incision is still markedly larger than the portal in phacoemulsion. Microincision Cataract Surgery (MICS) is an approach to cataract surgery through incision less than 1.8 mm with the purpose of reducing surgical invasiveness, improving at the same time surgical outcomes. Phacoemulsification requires expensive instrumentation which may not be available at all centres, whereas manual. Small Incision Cataract Surgery (SICS) requires only a minimum addition to the standard cataract surgery instrument armamentarium. Capsulorrhexis is mandatory for phacoemulsification, whereas manual SICS can be comfortably done with the envelope capsulotomy skills acquired previously.

Post-operative Care- The postoperative recovery period (after removing the cataract) is usually short. The patient is usually admitted only on the day of surgery, but is advised to move cautiously and avoid straining or heavy lifting for about a month. The eye is usually patched on the day of surgery and use of an eye shield at night is often suggested for several days after surgery. In all types of surgery, the cataractous lens is removed and replaced with an artificial lens, known as an Intraocular Lens (IOL), which stays in the eye permanently. Intraocular lenses are usually Monofocal correcting for either distance or near vision. Multifocal lenses may be implanted to improve near and distance vision simultaneously.