Cataract

What is a cataract?

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

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, halos, and dimness of color vision.

The progression of cataracts is highly variable; however, they will invariably worsen in severity with time. Changing glasses may sometimes be useful in improving vision as the cataract progresses. Besides changing glasses, the only other option for treatment of cataracts is cataract surgery.

Decision for Cataract Surgery

In general, the decision to treat cataracts 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. With today's technology it is no longer necessary to wait until a cataract is "ripe" before it can be removed.

Selecting the right intraocular lens power

All of the intraocular lenses discussed in this article have a common objective to improve one's quality of vision with less dependence on glasses after cataract surgery. To achieve this, an accurate preoperative measurement of the eyeball dimensions is critical. The IOL Master is a new, highly accurate device to measure a patient's eyes prior to cataract surgery. Unlike traditional ultrasound, this high precision instrument utilizes non-contact optical coherence biometry to measure the eye length and surface curvature. More accurate measurements will enable a more accurate determination of the intraocular lens power, allowing patients to become less dependent on glasses after surgery.

Selecting the right intraocular lens

When a cataract is removed, it is replaced with an artificial intraocular lens (IOL). There are a variety of IOLs that can be used in cataract surgery, and they each have their own set of advantages and disadvantages. No single IOL works best for everyone. So it is important for you and your ophthalmologist to discuss your particular circumstances and visual needs to customize a treatment plan and IOL selection that is most appropriate for you.

Fixed Focus Monofocal IOLs are used in the majority of cataract procedures. These lenses have the advantage of excellent quality of vision. Since these lenses have a fixed focal point which is generally set for distance vision, reading glasses are typically required for good near vision. For patients willing to use reading glasses for near tasks, these IOLs are an excellent choice.

Recent refinements in the optical quality of these lenses have allowed an even higher quality of vision than previously achievable. This new generation of IOLs include the Tecnis and Softec HD lens both of which reduces the aberrations of the eye's optical system, thereby improves contrast sensitivity and quality of vision in varying lighting conditions. Another option is the AcrySof IQ lens, which in addition to the improved optical quality, it also incorporates a yellow-tinted filter which is aimed at reducing the risk of progression of age-related macular degeneration.

Astigmatism refers to an optical irregularity of the eye caused by unequal curvatures of the natural crystalline lens and/or the cornea. Since an astigmatic lens or cornea has more curvature in one direction than another (similar to a football shape), as light enters the eye, the eye is unable to bend the light equally to focus images at any distance clearly. Limbal Relaxing Incision (LRI) performed during cataract surgery causes the cornea to heal in a more spherical shape. By precise measurements and careful surgical planning, these incisions are suitable for treatment of low levels of astigmatism. However, for moderate to high astigmatism, the resulting healing may at times be imprecise and unpredictable.

For those patients with moderate to high levels of regular astigmatism, the Acrysof TORIC intraocular lens is the most accurate means to reduce or eliminate the astigmatism at the same time of cataract surgery. This implant is specially designed to incorporate astigmatism correction, eliminating the need for additional LRI in many cases. Some patients with unusually high amounts of astigmatism may require a combination of both technologies to fully correct their astigmatism, which greatly improves the range of patients who can benefit from this treatment and their independence from glasses after surgery.

Presbyopia is progressively diminished ability to focus on near objects with age. As part of the normal aging process, the eye's accommodative abilities decline. By the fourth and fifth decades of life, most individuals will notice a decrease in their ability to focus on near objects due to a loosening of ciliary muscle tissue, a progressive decrease in the clarity and elasticity of the crystalline lens as well as an increase in the lens's thickness, which affects its length, curvature and optical power. These lens changes begin very early in life, but tend not to interfere with clear near vision until after the age of 40. At this approximate age, when the lens tissue has hardened and lost its ability to change its curvature sufficiently enough to focus for reading vision, the condition is called presbyopia. When presbyopia occurs, individuals require reading spectacles to fine-tune vision for near tasks such as reading or sewing.

Multifocal IOLs have highly specialized optical properties that can divide light to bring it into focus at more than one point at the same time. This allows the eye to see both near and far, usually without glasses. The ReSTOR and Tecnis Multifocal intraocular lenses use diffractive optical design to divide light into two focal zones so that near and distance objects can both be seen without glasses. While multifocal IOLs have a slightly greater tendency to cause night vision complaints than other IOLs, one can expect to enjoy spectacle freedom for both distance and near activities over 80% of the time with these lens implants.

Accommodating IOLs provide a full range of vision by using the eye's natural forces activated during accommodation to move the optic forward and/or backward, which simulates accommodation and enables many patients to enjoy multiple ranges of vision without spectacle or contact lens dependence. Examples of these types of intraocular lenses include the Crystalens and Tetraflex.

Having flexible hinge designs and simple monofocal optics mean that these IOLs offer increased flexibility for clear vision at varying distances without compromising the quality of vision. By nature of the lenses' dependence on the normal accommodating mechanism of the human eye, the near extent of clear uncorrected vision may vary between individuals.

For more information on specific premium channel IOLs currently offered by the surgeons at eyeMD Institute, please visit the websites below:

Monofocal premium channel IOL:

Softec HD - http://www.lenstec.com/lenstec/menu_hd.html

Tecnis - http://www.tecnisiol.com/

Monofocal astigmatic IOL:

Acrysof Toric - http://www.acrysofiqtoric.com

Bifocal IOL:

Acrysof ReSTOR - http://www.acrysofrestor.com/

Tecnis Multifocal - http://www.tecnismultifocal.com/

Accommodating IOL:

Crystalens - http://www.crystalens.com/

Tetraflex - http://www.thetetraflex.com/