Cataracts are a leading cause of blindness worldwide, accounting for nearly half of all blindness globally. According to the World Health Organization (WHO), nearly 20 million people worldwide suffer from poor visual acuity, of 3/60 or less, due to cataracts. These numbers are estimated to rise to 40 million by the end of 2020.
With populations of older individuals growing worldwide, this age-related disease has garnered great interest, especially regarding the cause of cataracts. Cataract research has involved studies using animals with induced cataracts as well as human lenses that have been removed from patients. Major focuses of interest in cataract research are potential underlying defects in the protein formation and structure of the lens as well as risk factors and control of the disease.
Certain research into the cause of cataracts has demonstrated a link between oxygen exposure and cataract formation, with some studies showing that statins (used to lower blood cholesterol) could have antioxidant effects that counteract the inflammation and oxidative stress that are thought to contribute to the development of cataracts.
In addition, eye drops containing acetyl-carnosine reduce the oxidation and glycation damage in the lens by reducing the cristallin cross-linking and could also help prevent cataracts. Furthermore, diets rich in the antioxidants lutein and zeaxanthin have been shown to reduce the risk of developing nuclear cataracts in some studies.
Cataracts can be classified using a grading system called the Lens Opacities Classification Scheme (LOCS III) which uses three slit lamp images to classify the type of cataract as nuclear, cortisol or posterior. This is achieved through comparison of the images with standard photographic transparencies. The cataract is further graded 1 to 5 according to severity.
Another slit-lamp based system is the Oxford Clinical Cataract Classification and Grading System (OCCGS), which uses diagrams and Munsell color samples to grade the cataract. These two systems have been shown to be comparable and are also highly reproducible. However, both are subjective techniques and an objective reproducible method is needed to standardize the grading system.
One new advance in cataract research is an imaging technique called Scheimpflug photography. This anterior eye segment analysis system can be used to objectively and accurately quantify the intensity and type of cataract. The advantage of this system is that it can create three-dimensional images of the lens by capturing several static slit images. This provides sixty images at three-degree intervals around a central axis, helping to show the degree of opacity and its exact location in the lens.
Wavefront aberrometry is another new technique that can be used to look at abnormalities in the whole eye and whole optical system. Previously used in corneal refractive surgery, the imaging technique is now being researched for its clinical use in cataract.
Reviewed by Sally Robertson, BSc