CATARACT AND PRESBYOPIA
A cataract is a clouding that develops in the crystalline lens of the eye or its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Cataracts typically progress slowly, causing vision loss, and are potentially blinding if untreated. The condition usually affects both eyes, but almost always one eye is affected earlier than the other. Cataracts develop for a variety of reasons, including long-term exposure to ultraviolet light, exposure to radiation, secondary effects of diseases (such as diabetes or hypertension), advanced age and trauma. As a cataract becomes more opaque, clear vision is compromised and a loss of visual acuity is noted. Contrast sensitivity is also lost, so that contours, shadows and colours become less vivid. Veiling glare can be a problem as light is scattered by the cataract into the eye.
A typical solution for cataracts is intraocular lens implantation. Many types of lenses have been developed. However, room for improvement exists in the following areas:
- Vision at all distances
- Quality of vision under all light conditions, including night and peripheral vision
- Presence of undesired optical phenomena
- Easy handling during eye surgery
- Occurrence of short- and long-term complications
Presbyopia is a condition where the eye is increasingly unable to focus on near objects. The exact mechanisms involved are not known with certainty. Research suggests a loss of elasticity in the crystalline lens, although changes in the curvature of the lens due to continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been postulated. Like grey hair or wrinkles, presbyopia occurs naturally with age. The first signs of presbyopia – eyestrain, difficulty seeing in dim light, problems focusing on small objects or fine print – are usually noticed between the ages of 40 and 50. The ability to focus on near objects further declines throughout life.
People with presbyopia can use reading spectacles as a solution. However, developments in advanced implantable lenses that can reliably restore long-term function offer hope of a medical solution for many patients in the near future.