The lens of the eye needs to be clear so that light can pass through it uninhibited and cast an image on the back of the eye (retina). Clouding or opacification of the lens of the eye, which is clear under normal circumstances, is known as a cataract. This usually develops over a long time, impairing vision and may ultimately lead to blindness if left untreated. Cataracts are most commonly seen in older people (senile cataracts) but congenital cataracts may be present at birth. The other types of cataracts that may be seen are traumatic cataracts that may occur after an injury to the eye, and secondary cataracts such as those occurring due to a medical condition such as diabetes. Cataracts may develop in one or both eyes.
There are various other causes of visual disturbances that may be similar to that of cataracts. It is therefore important that high risk patients, like those with diabetes, undergo routine screening. Cataracts develop gradually in most cases and may only be evident once it is significantly impacting on normal vision. A number of tests and diagnostic investigations will help to identify a cataract and differentiate from other ocular conditions.
The extent of vision loss and its effect on normal activities such as reading and driving will determine whether surgery is necessary at that point of time. The amount of visual impairment, indicating the severity of the cataract, can be determined by a comprehensive eye examination which may include one or more of the following investigations.
- Visual acuity test. A visual acuity eye test is similar to the routine eye test done throughout life by an optometrist or opthamologist (eye doctor). Each eye is tested individually by using an eye chart (Snellen chart) or a viewing device to determine the ability to see letters of gradually decreasing sizes. By this method, the doctor can assess to what extent the vision has been affected by the cataract. Visual acuity is a measurement of how well a person can see.
- Refraction test. This test will determine whether glasses can help to improve the vision.
- Contrast sensitivity testing. This test is similar to visual acuity testing but it shows more emphatically the decreased image contrast caused by a cataract, as a result of light scattering and glare caused by the cataract. The ability to differentiate between various shades of gray forms the basis of this test since this ability may be hampered in the presence of a cataract.
- Glare Testing. With a cataract, vision may be altered depending upon different lighting conditions, such as in brilliant sunshine and at night. These glare symptoms may be checked with different types of lighting by having a patient read the chart twice, once with and the next time without bright lights.
- Color vision testing. This test helps to detect acquired color vision defects, as may be seen in cataract patients.
- Potential acuity testing. this is a test that can give an approximate idea about the vision following cataract removal. It may be taken as the eye’s vision potential if there was no cataract.
- Slit-lamp examination. This is done with a special microscope known as the slit-lamp, which projects a thin, intense beam of light into the eye to give a magnified three-dimensional view of the interior of the eye. The doctor is able to examine in section the structures at the front of the eye, including the cornea, iris and lens, as well as the area between the iris and cornea, and look for any abnormalities.
- Retinal examination. Prior to this examination, the pupils are dilated with eye drops so that the back of the eye or retina may be visualized better. A slit-lamp or an ophthalmoscope is used to look for signs of cataract, as well as signs of glaucoma, macular degeneration, and other problems related to the retina and optic nerves which could be the cause of vision impairment.
- Tonometry. This test may be done to measure the pressure within the eye, or intraocular pressure (IOP), by means of a special instrument. Anesthetic eye drops may be instilled before conducting the test. Increased IOP may indicate glaucoma.
- Spectacular photographic microscopy. A specialized microscope is used to take a photograph of the endothelial layer of the cornea, which is a single layer of cells that regulates the water content of the cornea. This is usually done prior to cataract surgery to determine the health of the endothelium, which is likely to affect the outcome of surgery.
Various other tests may be suggested as necessary, such as the Amsler grid testing, fluorescein angiography, A-scan and B-scan ultrasonography, and tonography.
Once a cataract has been detected, the next step is to examine the treatment options. Treatment in the early stages may be simple, such as the use of eyeglasses, alternative lenses, anti-glare sunglasses, or just an adjustment in environmental lighting.
Drug therapy cannot cure a cataract. Mydriatic eye drops which dilate the pupils may help in some cases for a short period of time by increasing the amount of light entering the eye. It is sometimes prescribed for young children who are waiting for cataract surgery so as to prevent vision loss in the interim.
Surgery is the only effective treatment option in the case of more advanced cataracts, especially when it affects routine activities or when it is associated with other problems. Cataract removal surgery is safe and highly effective in improving vision. If the vision is not impaired significantly then surgery may not be necessary once a cataract is detected. Surgery can be delayed till later until the vision impairment is inconveniencing the patient’s life or is on the verge of doing so.
During surgery, the cloudy lens is removed and is replaced with an artificial lens. If there are cataracts in both the eyes which require treatment, surgery is usually done one at a time with an interval of 4 to 8 weeks between the two procedures. Phacoemulsification (phaco) is the most common procedure for cataract extraction, where the cloudy lens is broken up by a probe which emits ultrasonic vibrations and the particles are then removed by suction. The other surgical procedure is known as extracapsular cataract surgery, where the cloudy lens is removed as a whole. Intracapsular cataract surgery is rarely done nowadays, where the lens, along with its capsule, is removed. Cataract surgery is usually done on an outpatient basis.
Phacoemulsification usually does not take more than 30 minutes, while extracapsular and intracapsular cataract surgery may take a little longer. The different surgical procedures are discussed in detail under cataract lens removal and replacement surgery.