Contact Lenses Care

Though many factors should be considered during the discussion between you and your contact lens specialist, generally, hard lenses will be the lens of choice if you:

• Must have the sharpest visual acuity possible.
• Have a high amount of astigmatism.
• Have moderately “dry eyes.”
• Are concerned about the cost.
• Use topical eye medications.
• Prefer an easy lens care system.
• Desire a durable lens.

NEW DEVELOPMENTS IN COMFORT

One of the reasons for rigid-lens failures is due to the fact that PMMA allows neither oxygen-rich air nor oxygen-rich tears to pass through it. Your cornea needs oxygen to remain healthy; in hard lenses it relies mainly on the tears that flow under the lens and are replenished with each blink. If the tears‘ supply of oxygen isn’t sufficient, the lens is uncomfortable and can’t be worn for very long. (Gas-permeable contact lenses, which are not made of PMMA, are a big threat to the future of conventional hard contact lenses because they retain most of the hard lens’s advantages and few of their disadvantages. Another cause of discomfort in hard lens wear is the constant rubbing of the upper lid as it crosses the inflexible lens edge during each blink. Standard lenses are being made more comfortable in several ways to overcome these discomforts.

SIZE AND THICKNESS

The modern conventional rigid lens is usually between 8 and 10 mm in diameter and doesn’t cover the cornea completely. Earlier hard lenses were much larger and covered not only the cornea, but the sclera (white part of the eye) as well. Over the decades improved fitting and manufacturing techniques have allowed the lenses to gradually shrink in diameter and thickness. Now we even have “ultra-thin mini-lenses” with a center thickness of .035 mm and less than 8 mm in diameter. These contacts are very comfortable for a hard lens but difficult to fit, since they have to be centered perfectly over the pupil. Unlike the larger lenses, which have a large tolerance of movement without adversely affecting vision, these small thin lenses should move only slightly with each blink; otherwise blurred vision will occur. If a cornea is too steep or too flat or has too much astigmatism, the mini-lens should not be prescribed. For people who can wear them, however, small, thin lenses are more comfortable for several reasons. Well-fitted ones are more likely to float on a layer of tears and less likely to touch the cornea, so there’s less sensation. They also touch the lids less, further increasing comfort. In addition, small lenses that are thin enough to flex during the blink help tear circulation, thereby reducing the possibility of overwear syndrome. (The larger the lens, the greater the distance tears have to travel once they’ve entered under the lens edge. By the time they reach the center of the cornea, much of the oxygen has been depleted.) Contacts must, however, remain large enough to cover a fully dilated pupil so that night vision isn’t adversely affected. Thin mini-lenses must also be handled more carefully to avoid loss and warpage.

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