Tuesday, May 2, 2017

Brief Summary of Cataract

A common cause of vision loss, a cataract is a gradually developing opacity of the lens or lens capsule of the eye. Cataracts commonly occur bilaterally, with each progressing independently. Exceptions are traumatic cataracts, which are usually unilateral, and congenital cataracts, which may remain stationary.
Cataracts are a part of aging and are most prevalent in patients older than age 70. Surgical intervention improves vision in 95% of affected people.
Cataracts have various causes, depending on their type:
Senile cataracts develop in elderly patients, probably because of degenerative changes in the chemical state of lens proteins.
Congenital cataracts occur in neonates as genetic defects or as a result of maternal rubella during the 1st trimester.
Traumatic cataracts develop after a foreign body injures the lens with sufficient force to allow aqueous or vitreous humors to enter the lens capsule.
Complicated cataracts develop as secondary effects in patients with uveitis, glaucoma, retinitis pigmentosa, or a detached retina or in the course of a systemic disease, such as diabetes, hypoparathyroidism, or atopic dermatitis. These cataracts can also result from exposure to ionizing radiation or infrared rays.
Toxic cataracts result from prolonged drug or chemical toxicity from prednisone, ergot alkaloids, naphthalene, or phenothiazines; they also result from excessive exposure to sunlight.
Signs and symptoms
Characteristically, a patient with a cataract experiences painless, gradual blurring and loss of vision. As the cataract progresses, the normally black pupil turns milky white (in extreme cases). Otherwise, lens opacity is revealed during a slit-lamp examination.
Some patients complain of blinding glare from headlights when they drive at night; others report an inability to recognize people or things at a distance. Patients with central opacities report better vision in dim light than in bright light because the cataract is nuclear and, as the pupils dilate, patients can see around the lens opacity.

When shining a penlight on the pupil, observation of a white area behind the pupil suggests an advanced cataract. Ophthalmoscopy or slit-lamp examination helps to confirm the diagnosis by revealing a dark area in the normally homogeneous red reflex.
Surgery is indicated when the patient complains of functional visual impairment. Cataracts require surgical extraction of the opaque lens and intraoperative correction of visual deficits with a lens implant (intraocular lens) for best visual results. This procedure is usually performed as same-day surgery.
Surgical procedures
Extracapsular cataract extraction removes the anterior lens capsule and cortex, leaving the posterior capsule intact. Typically, this is done using phacoemulsification equipment, which fragments the lens with ultrasound. The fragments are then removed by irrigation and aspiration. With this procedure, a posterior chamber intraocular lens is implanted where the patient’s own lens used to be. This procedure can be used with patients of all ages.
Some patients who have an extracapsular cataract extraction develop a secondary membrane in the posterior lens capsule (which has been left intact), which causes decreased visual acuity. But this membrane can be removed with a laser, which cuts an area out of the center of the membrane, thereby restoring vision. However, laser therapy alone can’t be used to remove a cataract.
Intracapsular cataract extraction removes the entire lens within the intact capsule by cryoextraction (the moist lens sticks to an extremely cold metal probe for easy and safe removal with gentle traction).
Complications of surgery include the loss of vitreous (during surgery), wound dehiscence from loosening of sutures and flat anterior chamber or iris prolapse into the wound, hyphema, pupillary block glaucoma, retinal detachment, and infection.
Correction of visual deficits
A patient with an intraocular lens implant may experience improved vision almost immediately if the retina is intact. The implant usually corrects only for distance. To protect the eye postoperatively, some patients wear an eye patch for 6 to 8 hours, whereas others may wear a collagen shield (similar to a contact lens) that dissolves in 24 hours. The patient will then need either corrective reading glasses or a corrective contact lens, which will be fitted 4 to 8 weeks after surgery.
If no lens has been implanted, the patient may be given temporary aphakic cataract glasses; in about 4 to 8 weeks, he’ll be refracted for his own glasses.

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