Presbyopia is considered a refractive error in the same category as nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. It is considered a result of the natural aging process, as hardening of the lenses causes inability to focus on near objects.
Definition & Facts
When aging causes the lens of the eye to harden, the eye is unable to focus light directly on to the retina, as in normal vision. Light is instead focused behind the retina, missing the target for up-close vision and resulting in blurred vision. Youthful eye lenses are soft and flexible, which allow the muscles of the eye to reshape focus in response to near or far vision.
People over the age of 35 are at risk for presbyopia. People with vision disorders like far-sightedness are more likely to experience early presbyopia, as are females. Presbyopia can arrive in tandem with astigmatism or near-sightedness as well.
Symptoms & Complaints
Brighter light becomes necessary to read, as light closes the pupil and constricts the lens for better viewing. Reading late at night may present problems due to tiredness of eye muscles working to contract the lens.
For most people, presbyopia is an inevitable part of aging. The age-related stiffening is caused by changes occurring in the proteins within the lens and the muscle fibers surrounding it.
Certain medical conditions, like diabetes mellitus and cardiovascular disease can cause people to experience presbyopia earlier than the age of 35. Both of these diseases may limit blood supply to the eye, thereby reducing oxygenation and causing stiffening of tissue. Certain drugs, such as antidepressants, diuretics and antihistamines have also been linked to premature presbyopia.
Diagnosis & Tests
A regular eye examination will detect presbyopia. Special eye drops will be given to dilate the pupil of the eye. Dilation helps the ophthalmologist to view the inside of the eye and evaluate the retina and test the eye muscles.
A vision test or refraction test of letters will determine ability to see at a distance and close-up. The doctor will measure ability to focus, see color, pupil health and side, or peripheral vision. A retinoscopy may be performed which determines how light reflects off of the retina. It can detect refractive errors.
Treatment & Therapy
Many people will simply buy an inexpensive pair of 'readers' from the pharmacy, and those who already wear eyeglasses to correct vision will frequently opt for a bifocal vision aid built into the lens.
The most popular bifocal today is called a progressive lens which eliminates the tell-tale line in bifocals, giving certain aesthetic and visual advantages over the former bifocal solution. Progressive lenses act more like the natural eye, providing several lens powers that seamlessly progress from one view to the next.
Contact lenses are made to correct presbyopia. Some of them have bifocals built into the lens, but many times, these are difficult to fit and do not satisfy vision requirements. Monovision contact lenses are satisfactory to many wearers. They provide distant viewing in the dominant eye and close vision in the other.
LASIK, or laser-assisted in-situ keratomileusis is the construction of a flap in the cornea and then the reshaping of the outer layer of the cornea, changing the curve. If thinning of the cornea has occurred with aging, this procedure is not recommended. Photorefractive keratectomy is very similar to LASIK, but the epithelium is removed and grows back, adhering to the reshaped cornea.
Because presbyopia is a progressive disorder, neither of these procedures may offer a permanent solution. Lens implants are available in many different formats, and they are considered fairly satisfactory. Some of the side effects are blurring and glare at night, and implants carry the risks of any surgery such as infection.
Some success has been reported via a treatment that inserts a tiny plastic ring at the edges of the cornea, changing its curve through pressure. Various kinds of corneal inlays (keratophakia) are being developed or are available. The inlays available seem satisfying for near and far vision and night vision. The biggest advantage is, if they are not satisfactory, they can be removed, unlike refractive surgery, which is permanent.
A new, topical treatment for presbyopia is being tested. The treatment is an eye drop with a formula that causes the lens to become more flexible via reducing the cross-linked protein which stiffens the lens. Random, double-blind studies showed very positive results for the eye drop. The drops were also well-tolerated and showed no appreciable side effects.
Prevention & Prophylaxis
- Controlling health conditions like diabetes and high blood pressure (hypertension). High blood pressure damages the tiny capillaries feeding blood to the eyes, as does diabetes. Complications of diabetes include blindness. Medication, diet, and regular exercise can help prevent these conditions.
- Having one's eyes checked regularly, even if vision seems good.
- Wearing protective eyewear during tasks like mowing the lawn or blowing leaves.
- Eating foods that contain high levels of antioxidants, like leafy greens and vegetables.
- Doing close work with good lighting, so eyes needn't strain to see.
- Making sure glasses prescriptions are up-to-date.
- Addressing symptoms like blurred vision, which may be a sign of presbyopia or something more serious.