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Understanding the Eye: Cataracts

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  What is a cataract?   Cataract Surgery

 What is a Cataract

A cataract is an opacity or cloudiness in the natural lens of the eye. It is still the leading cause of blindness worldwide and represents an important cause of visual impairment in the United Kingdom. The development of cataracts in the adult is related to ageing, sunlight exposure, smoking, poor nutrition, eye trauma, systemic diseases, and certain medications such as steroids.

Just as a smudged or dirty camera lens may spoil a photograph, opacity in the natural lens of the eye can result in a blurred image. Patients with cataracts usually complain of blurred vision either at distance, near, or both. This may interfere with tasks such as driving or reading. Other common complaints include glare, haloes, and dimness of color vision.

A diagnosis of cataract can only be made by a thorough eye examination including slit lamp (microscopic) evaluation. Other devices are sometimes used to determine if glare interferes with vision. If cataract surgery is being considered, an ophthalmologist will also examine the posterior aspect of the eye, which will include evaluation of the retina and optic nerve. If a cataract is mature (extremely dense) or hypermature (white), an ultrasound device known as a B-scan may be used to rule-out retinal detachment and ocular tumors prior to proceeding with cataract surgery.
  Clear Lens

The progression of cataracts is highly variable, however, they will invariably worsen in severity. Changing glasses may sometimes be useful in improving vision as the cataract progresses, since cataracts may induce relative nearsightedness This is the answer as to why some patients with hyperopia (farsightedness) will actually have better vision without glasses in the early stages of cataract development. For most patients, however, changing glasses has minimal impact on overall visual quality. Besides changing glasses, the only other option for treatment of cataracts is cataract surgery.

The decision for cataract surgery is reached only between the ophthalmic surgeon and the patient. In general, this decision is based on the degree to which the patient's vision is impaired, and the impact that impairment has on his or her quality of life. When a patient is significantly bothered by symptoms of cataract, cataract surgery is usually offered. Many patients will ask if a cataract must be "ripe" before surgery. The answer with today's technology is "no." Before the development of small incision cataract surgery and intraocular lens implants, outcomes with cataract surgery were far inferior to outcomes today. Therefore, ophthalmologists would typically wait until a cataract was very advanced before offering surgery. Today, with advanced surgical techniques and equipment, cataract surgery can be offered at a much earlier stage. In fact, many ophthalmologists will agree that it is safer to proceed with cataract surgery at an earlier stage of development rather than waiting until the cataract is advanced and very dense.

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 Cataract Surgery

Cataract surgery today is typically performed using a microincisional procedure. To the patient, this means minimal discomfort during or after surgery, a more speedy recovery of vision, and reduced risk of induced astigmatism. This means less dependence on glasses afterwards. The major steps of cataract surgery are detailed below using a microincision procedure, phacoemulsification (ultrasonic cataract removal), and a foldable lens implant. This type of procedure is considered state-of-the-art for cataract surgery today. The procedure demonstrates basic principles only.
The most commonly used cataract incision is about 3 millimeters in size - just about one-eighth of an inch! Because of the careful construction of this incision, and its small size, the incision is generally self-sealing. This translates to a "no-stitch" type operation.   Phacoemulsification Cataract Surgery
The surgeon then creates an opening in the capsule, which is a micro-thin membrane surrounding the cataract. This procedure, called capsulorhexus, requires extraordinary precision since the capsule is only about four-thousandths of a millimeter thick. This membrane is actually thinner than a red blood cell and the surgeon must delicately remove the capsule while manipulating instruments within the anterior chamber - a space only 3 millimeters deep.   Capsularhaxis
Phacoemulsification is the aspect of the procedure in which ultrasonic vibrations are used to break the cataract into smaller fragments. These fragments are then aspirated from the eye using the same instrumentation.  
The surgeon may elect to create grooves in the cataract, and subsequently break the cataract into smaller pieces using the phacoemulsification tip and a second instrument passed through a smaller "side-port" incision.
The lateral view of the procedure shows the phacoemulsification tip being placed into the substance of the cataract by the eye surgeon. The "phaco" aspect of the procedure is used to remove the denser central nucleus of the cataract.
Once the denser central nucleus of the cataract has been removed, the softer peripheral cortex of the cataract is removed using an irrigation/aspiration handpiece. The posterior or back side, of the lens capsule is left intact to help support the intraocular lens (IOL) implant.
The intraocular lens is often folded and passed through the tiny incision where it is opened (implanted) inside the "capsular bag". In this illustration, the lens is being inserted via an "injector". This is an instrument designed to help keep the incision size small while allowing implantation of a 6 millimeter lens through a 3 millimeter (or even smaller) incision.
The IOL is shown here implanted within the "capsular bag" where it is neatly centered. The springy "arms" of the IOL, known as haptics, hold the lens implant within the capsular bag. The IOL does not generally require sutures to remain in good position.  
This lateral view of the IOL implant shows the lens within the "capsular bag," which is the desired location. This position is the same as that of the natural lens (cataract) of the eye and, therefore, is generally tolerated best and provides the most optimal visual results. At this stage, the cataract operation with IOL implantation is complete.  

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