By Eyecare NGOverview | Causes | Signs | Diagnosis | Treatment
Presbyopia is a normal age-related condition in which the eye gradually loses its ability to focus on near objects. Over time, it becomes increasingly difficult to perform near tasks with the unaided eye.
At about the age of 40, most people begin to experience some difficulty reading tiny prints. While some people may experience this earlier or later, at some point, everyone experiences it. Generally, people with hyperopia (long-sightedness) tend to develop presbyopia earlier than people without refractive errors while those with myopia (short-sightedness) tend to develop it later than those without refractive errors.
Many people in Nigeria live with uncorrected presbyopia, increasing the burden of avoidable visual impairment in the country. Visual impairment due to uncorrected presbyopia affects the quality of life, reduces productivity and can cause job loss due to the inability of an affected person to carry out the near tasks he or she used to do.
What causes presbyopia?
In childhood and early adulthood, the lens in the eye is flexible and can easily change shape to bring objects at different distances into focus. While looking at an object at a distance, the lens is relaxed and flat, but when you change focus to an object nearby, the lens curves or bulges to adjust its focusing power so as to bring about clear vision at near. This process by which the lens adjusts its focusing power as you change focus from a far object to a near one is known as accommodation.
As we get older, the lens gradually hardens making it less flexible and unable to change its shape to accommodate for near vision. Hence, vision gets blurry while performing near tasks.
Signs and symptoms of presbyopia
- Difficulty performing near tasks such as reading tiny prints, threading a needle or picking stones from grain.
- The tendency to move reading material and objects away to see clearly.
- Headaches and brow ache after reading or doing close work.
- Eye strain and fatigue.
Diagnosis of presbyopia
Presbyopia is diagnosed during an eye examination. It is usually diagnosed by checking your near visual acuity and carrying out refraction. While the visual acuity test determines the extent to which you can see while reading small prints on a standard card placed at 40cm, refraction determines the lens prescription that will compensate for the accommodative error observed and help you see clearly.
Treatment of presbyopia
Presbyopia can be corrected using eyeglasses, contact lenses or surgery
Eyeglasses (spectacle lenses)
This is the most common and cheapest means of correcting presbyopia. There are many lens types to choose from depending on your preference, occupation and whether there is an existing refractive error. Lenses could either be single vision lenses, bifocals, trifocals or progressive lenses.
Single vision lenses are lenses that have a single prescription all over. For the correction of presbyopia, they are usually prescribed as reading glasses. This means you can only put them on when you need to do some near tasks such as reading. If you try to look at a distant object with reading glasses, you will experience blurring of vision.
Bifocal lenses are lenses that have two prescriptions on them. One prescription is located at the top of the lens (for distance vision) and the other prescription is located at the bottom (for near vision). There are different types of bifocals based on the style of the bottom or reading segment of the lens.
- D top: This is also known as flat top. The reading segment of the lens has the shape of a D turned to its side with the flat part facing up.
- Roundtop: The reading segment of the lens has the shape of a semicircle
- Blended: Also known as invisible bifocal. It is similar to the round top but the demarcation between the distance and near segments of the lens is not visible.
Trifocal lenses, though no longer readily available, are prescribed when there is a need for good intermediate vision (vision in between distance and near). The lenses are made of three segments demarcated by two horizontal lines. It is not cosmetically appealing to most people.
Progressive lenses are the most modern lenses available for the correction of presbyopia. The power of the lens increases gradually from top to bottom enabling the wearer to have clear vision at almost all distances. Compared to bifocals, it takes a little more time to adapt to progressive lenses and they are more expensive. However, they are more cosmetically appealing because of the absence of visible segments on them.
In the past, presbyopia was corrected mainly with eyeglasses. In recent times, contact lenses are increasingly being used to correct presbyopia.
Just like eyeglasses, contact lens types include single vision lenses, bifocals, and multifocal lenses. To correct presbyopia with single vision contact lenses, the eye doctor corrects one eye (the dominant eye) for distance vision and the other eye (non-dominant eye) for near vision. This is known as the monovision technique. In this case, the eyes focus appropriately depending on the whether they are viewing an object at distance or near. Over time the two eyes may adapt to viewing both distance and near objects together. Alternatively, single vision contact lenses may be prescribed to correct distance vision and a pair of reading glasses given for near vision.
There are quite a few surgery options for the correction of presbyopia. One is the corneal inlays. The corneal inlays use the monovision technique to correct presbyopia. It involves the surgical insertion of a small lens in the corneal tissue directly in front of the pupil in the non-dominant eye so as to improve near vision in that eye without affecting distance vision.
Other surgical options include laser surgery, and natural lens extraction and its replacement with multifocal or accommodating intraocular lens.