Contact Lenses Care

Conventional soft contact lenses cannot be used to correct moderate to large amounts of astigmatism. Their pliable nature causes them to conform to irregularities in the shape of the cornea and thus duplicate the astigmatic refractive error. Hard contact lenses are firm and hold their shape; they are able to correct high amounts of astigmatism because the spherical undersurface of the lenses and the tears beneath them create a new, smooth optical surface.

Until recently, therefore, patients had two contact lens options: to either wear a hard lens and get sharp vision, or wear a conventional soft lens and live with less-than-perfect vision. Now there is a new type of soft contact lens, the toric lens, which give astigmatics a third choice. While it is still in the early stages of use and development, this lens will eventually be perfected, and will certainly be a part of the professional contact lens practitioner’s armamentarium.

Currently the cost of such lenses is about half again as much as conventional soft lenses; they are technically difficult to manufacture; production and delivery tend to be slower than for conventional lenses; duplication is difficult; and they are trickier to fit. In addition, they don’t always produce a favorable or predictable visual correction. This is due in part to the problem of lens rotation, which the toric lens shares with the bifocal lenses discussed earlier. As soon as the lens rotates on the eye, the axis of astigmatism becomes displaced and the vision becomes blurred, particularly when the astigmatism is severe. To solve this problem, a variety of solutions have been devised, similar to those used to stabilize bifocal contact lenses.

Most commonly, prisms are placed in the lower parts of the lenses; the added plastic orients the lens by using gravity to keep the lens in alignment. Or a small segment may be cut off the bottom of the lens; this truncation results in a straight edge that stays aligned and parallel with the edge of the bottom eyelid. A lens may have the top or bottom portions or both portions made especially thin so they remain aligned underneath the eyelids; this is known as slab off. Finally, orientation grooves, a series of tiny vertical lines, may be cut into the top edge of the lens. The inner surface of the upper eyelid crosses the grooves, and with each blink the lid pulls the lens toward the top, keeping the lens oriented.

Most people think that cataracts develop only in their grandparents. In fact, though the average patient is seventy years old, cataracts can occur in anyone from the time of birth to over one hundred years of age. Another misconception is that a cataract is a film growing over the eye, when in reality it is the natural, transparent, crystalline lens of the eye that becomes cloudy. The light rays passing through the cloudy lens become obstructed and vision becomes more and more blurred as the condition worsens. Most often cataracts are part of the normal aging process, but they may also be caused by injury, disease, birth defects, infection, vitamin deficiency, radiation, and enzyme deficiencies.

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