Presbyopia

PRESBYOPIA

Presbyopia is an eye condition associated with aging. It’s common among people who fall under the age group between 40 and 50 years.

Usually, when you switch from looking at something at a distance to something up close, the lens in your eye changes shape in order to focus on the close object. With age, the lens loses its elastic qualities and hence the ability to clearly see small things up close. Fine objects close to you look blurred. Although this condition gradually worsens, it does not cause blindness and can easily be corrected with bifocals or reading glasses. It is not the same thing as farsightedness.

Causes

People with no refractive error tend to notice presbyopia in their mid-40s. Whereas people with farsightedness detect presbyopia earlier, especially when they are not wearing their glasses.

Though it’s largely an age related condition and affects alomost everyone, other conditions like diabetes can result in an earlier onset of presbyopia.

Signs & Symptoms

Difficulty in reading fine print up close is the most common indicator, besides decreased focusing ability, eyestrain and frequent headaches.

People with presbyopia must hold reading material farther from their eyes. Nearsighted people may need to take off their distance glasses to read. So if you have trouble reading the newspaper or threading a needle, it’s time to see a doctor.

Another symptom of early presbyopia is when distance vision stays blurred a few moments after a person looks up from reading. The symptoms become worse with fatigue.

Diagnosis

The reading card is the most basic test for presbyopia. The patient reads a card with various sized letters and numbers, held 14 or 16 inches away. The patient is then allowed to try different lenses to ascertain what correction is needed.

This is followed by a general eye examination and tests to determine various measurements:

• Visual acuity test
• Refraction test
• Muscle integrity test
• Slit-lamp test
• Retinal examination

Treatment

People diagnosed with presbyopia need not go in for correction immediately after symptoms begin, at least for a year or two. Some simple steps can help ease the reading difficulty, like:

• Changing the reading distance
• Increasing illumination
• Taking frequent breaks while reading
• If nearsighted, removing the regular glasses to read

Correction of presbyopia would involve compensating for the lost accommodative power of the lens of the eye. This is achieved by using a plus lens, which is quite similar to a magnifying lens. And as the lens of the eye continues to change with age, upgrading to a stronger reading glass is required every two years until the mid-50s or 60s. Little change is needed after that, provide that other visual problem don’t develop.

Several options are available for correcting presbyopia. For most, reading glasses would do the job. Here the whole lens of the eyeglass contains the necessary correction for reading. Which lets you see close objects clearly, but makes distant objects look blurred. For that reason, reading glasses must be removed to see objects in the distance. These glasses are recommended for those who don’t mind switching between two glasses – for reading and otherwise, those who don’t need distance correction and for those who wear contact lenses for distance vision. They are also prescribed for people who cannot wear bifocals.

Reading glasses can be obtained with or without a prescription. Over-the-counter glasses are also available and they cost much less than custom-made glasses. Even the readymade type of glasses is very effective and suits most patients.

People who do not need glasses for distance vision may only need half glasses or reading glasses. Half-glasses leave the top of the glasses open to facilitate distance vision without the need to remove the glasses.

Then there are bifocals, which have two lenses in one. One segment, usually the one at the bottom, is made to adjust the eye for close focus, and the other one has a different strength for distant focus. Wearing bifocals require patients to make some adjustments, as they need to learn to automatically look through the proper part of the glass.

Images through the lower segment look like they are in a slightly different place than they really are. As the plus segment magnifies objects, things appear closer to the wearer than they really are. Walking down stairs may be difficult until the person learns to hold a different head position. And as the eyes cross the junction of the distance and near segments, the image jumps up for a split second. Some styles of bifocal lenses can lessen this image jump.

But after the initial problems of getting used to the glasses, most people find bifocals quite convenient. And for people concerned about their appearance, invisible bifocals or bifocal contact lenses may also be an option.

Invisible bifocals are glasses that don’t have a visible line dividing the upper and lower segments. These seamless bifocals have the segment line polished so that it is not visible as a distinct line. In the area where both the segments blend, some blurry vision results. This means the wearer experiences more difficulty getting adjusted.

Patients can also opt for a progressive addition lens or variable-power lens. This has no visible line either. This acts like a trifocal lens that provides clear vision for far distance, intermediate distance and short distances as well. But, unlike bifocals or trifocals, it has a gradual change in power over the area of the lens. With this, objects below the line of direct vision and to the side are somewhat blurred. Progressive addition lenses often take longer to adjust to and may cost more than bifocals.

Contact lenses can be used to correct one eye for near vision and one eye for far vision. This is termed “monovision”. It eliminates the need for bifocals or reading glasses, but can interfere with depth perception.

Contact lenses that can correct for both near and far vision with the same lens are also prescribed for some. But bifocal contact lenses aren’t as successful as conventional single-vision contact lenses and some find it extremely inconvenient. The problems associated with bifocal lenses are fluctuating distance vision and poor near vision. But those opting for contact lenses find better image quality with rigid gas- permeable lenses than hydrogel (soft) bifocals.

Trifocals are prescribed for people with difficulty seeing clearly at an intermediate distance (3-5 feet away) with bifocals. These lenses have a middle section to correct vision for midrange distances. A person wearing trifocals looks through the top segment to see distant objects, through the middle to see just past arm’s length and through the bottom to see close objects.

For choosing the right kind of reading glasses, it is important to take into consideration the patient’s occupation, hobbies and visual needs.

There are some new surgical procedures that patients can explore, to do away with wearing glasses or contacts.

References

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• “http://lasik.wustl.edu”

• “http://www.uic.edu”

• “http://www.nlm.nih.gov”

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