The more you know about cataracts, the easier it is to focus on cataract prevention.
What is a cataract?
At birth, with rare exceptions, most of us arrive in the world with a clear crystalline lens within each eye. The pathway of our visual images start with light passing through the cornea (the clear front window of the eye), through the pupil (the opening in the center of the iris, or colored portion of the eye) and through crystalline lens which functions to focus light onto the center of the retina (the film of the eye). The retina, via the optic nerve, will then transmit visual images to the brain. When the crystalline lens becomes opacified (cloudy), this system becomes disrupted, and vision becomes impaired. Opacification of the crystalline lens is called “cataract”, and there are many variations in appearance and type and many causes and can present at any age. The word cataract originates from the Greek word “cataracta”, which means waterfall. The ancient Greeks used this term as they noticed a similarity in the appearance of the white opaque rushing water of a waterfall and the appearance of a white mature cataract.
To understand the different types of cataracts and causes, it is important to understand the anatomy of the lens. Using a metaphor, the lens anatomy can be compared to a Peanut M&M candy™. There is an outer candy coating (the lens capsule), a chocolate layer inside (the lens cortex), and a peanut in the center (the lens nucleus).
The most common cause of a cataract is an age related nuclear clouding which is due to long term accumulation of metabolic and oxidative waste products within the lens and possibly UV-B/Sunlight light exposure. Cortical clouding (within the cortex of the lens), due to similar causes, is also a common cause of an age related cataract.
Cataracts can occur earlier in life with poorly controlled diabetes resulting in cortical and nuclear cataract. Patients who are exposed to steroid medications in any form (orally, topically as eye drops, skin creams etc.) are at an increased risk to develop a posterior subcapsular (PSC) cataract which occurs on the posterior lens capsule. PSC cataracts can have a much more abrupt and earlier onset in life than nuclear or cortical cataract. Smoking has also been known to predispose patients to formation of a PSC cataract. Other less common varieties of cataract can occur with any trauma to the eye or even present at birth as a congenital cataract with a large variety of causes.
What can be done to prevent cataracts?
I often joke with patients that a cataract is such a common occurrence that just like birth, death, and taxes, it is an issue we must all face at some juncture in life (hopefully later than earlier). I am often asked if there are any dietary measures or vitamin supplementation to reduce the formation of a cataract, however this is not as well studied as the use of vitamins in the prevention of macular degeneration. Several scientific epidemiological studies following populations over many decades have shown some merit however that using multivitamins regularly (Vitamin B6 and B12, Vitamin C, beta carotene, antioxidants and possibly lutein and zeaxathin) can reduce the degree of lens opacification over time. As with all medications, you should consult with your physician before deciding to use any vitamin supplementation to clarify if you have any contraindication to using them.
There is conflicting evidence regarding the role of UV-B exposure in sunlight as a causative agent for cataracts. There is some support that using sunglasses on a regular basis to block UV-B light may help to reduce cortical cataract formation. Smoking cessation can also help to reduce the formation of cataract. If a patient is diabetic, strict blood sugar control is also an important measure to reduce the formation of a cataract. If possible, reducing or avoiding the use of steroid medication can reduce the formation of a PSC cataract.
What can be done if a cataract is worsenening and glasses cannot help improve vision significantly?
If you are experiencing gradual painless loss of vision, you should consult with your ophthalmologist as cataract can be a common cause. If you are found to have cataract formation, there is generally a shift in the glasses prescription in the early stage. Having your glasses prescription checked to see if your vision can be improved with glasses is the first step in determining how significant your cataract has become. If glasses are not able to sufficiently improve your vision and your daily activities are affected by the decrease in vision your experience, you may be a candidate to have cataract surgery.
Modern cataract surgery has improved a tremendous degree compared to decades earlier. It is the most common and successful surgery in the world, and is typically performed on an outpatient basis with topical anesthetic and often without any sutures or eye patch. Prior to surgery the pupil is dilated, and once in the operating room, a small self-sealing incision is made on the side of the cornea. The surgeon then makes a circular opening in the anterior lens capsule (the candy coating of the peanut M&M), and uses an ultrasound instrument to emulsify and vacuum out the nucleus (the central peanut), and remove the cortex (the chocolate layer). The inside of the lens capsule is polished and an intraocular lens is folded and introduced into the eye through the corneal incision and seated into the remaining lens capsule to conclude the surgery.
Prior to surgery, measurements are taken to determine the power of lens necessary to achieve the best vision after surgery based on the curvature of the cornea and anterior-posterior length of the eye. Intraocular lenses (IOLs) can potentially have several features depending on a patient’s needs. The most common IOL used is a monofocal lens, which does not typically require an additional out of pocket expense. This lens is chosen to have a point of focus either for distance vision (driving, TV) or near vision (reading), but not both. Typically patients who have the monofocal lens will choose to have distance focus and use reading glasses for near vision. There are multifocal/accommodating IOLs available for patients who are appropriate candidates, to allow the patient a larger range of vision at far, near and intermediate (computer) distance and may allow great independence from glasses. There are still other IOLs which can correct astigmatism (a special type of glasses prescription) at the time of cataract surgery. After discussion of the patient’s needs and preferences, the surgeon can best advise their patient regarding which type of IOL may best suit them.
Anand B. Bhatt, MD
Assistant Professor of Glaucoma and Cataract Surgery, Gavin Herbert Eye Institute
UC Irvine School of Medicine