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Q: What are disposable contact lenses? | Ask Dr. Chet

A: Disposable contacts are based on a very simple premise: the more often they are replaced, the clearer they stay, the more comfortable they are, and the healthier they are to wear. Soft lenses are made of a porous material and contain a significant amount of water so many parts of our tears are absorbed into the matrix of the lens.

Oil, mucus, calcium and especially protein, build-up in and on the surface of the lens and no matter how well one might clean and disinfect (many wearers don't do one or either) the lens still collects this debris. Over time the lens transmits less oxygen, which is needed to keep the cornea healthy. With less oxygen transmission, the eye is at increased risk of infection and other complications.
There is no better way to keep contacts clean than to replace them on a frequent basis. This is what makes disposable contact lenses so attractive and why Dr. Chet recommends that all soft-lens wearers use them.

Any contact lens that is replaced on a regular schedule can be considered a disposable lens. By convention, today's disposable contacts are replaced on three schedules depending on the lens design and Dr. recommendation.

Quarterly replacements are the least frequently discarded. These are usually non-disposable products that manufacturers sell in multiples at a reduced price to make it more attractive to replace sooner than one-year. Some of the most complicated astigmatic prescriptions fall into this category.

The most common replacement schedules are weekly to monthly. Most prescriptions can be filled with these lenses, as most manufacturers make these kinds of lenses. Single use lenses are the latest addition to join the disposable lens arsenal. For occasional wearers what could be better than putting on a fresh pair each time? These are available mostly in simple near and farsighted designs.

Q: My prescription is very strong. The thin lenses I got a few years ago aren't that thin looking I.e. "the coke bottle effect." Can you do any better? | Ask Dr. Chet

A: While newer and thinner lens materials have been introduced in the past few years, and some new ones in the final stages are awaiting FDA approval, one of the most important factors that influences edge thickness is the size of the lens. Nearsighted (minus) lenses are thinner at the center and thicker at its edge. Therefore, smaller lenses are thinner.

The simple fact is that finding the smallest size frame that look good on your face, combined with the newest thin lenses will result in the best looking lenses possible. An additional feature that helps to hide as much thickness as possible is a wide side-edge such as with a plastic frame. If the side-edge of a metal frame is 1 to 1½ mm, and the side-edge of a plastic frame is 3 to 5 mm that lens edge in a plastic frame looks thinner because more is hidden.

All those factors and more are considered at Visual Effects Optical.

Q: I love my new progressive bifocal, but why don't they work so well at my computer? | Ask Dr. Chet

A: Progressive Addition Lenses have a variable focus that allows for clear vision from distance through near; today's newer designs have been compressed to fit into smaller size frames. While Progressive Addition Lenses work great for almost all situations because of that variable focus ability, computer work is a tough situation for many people with no great solution for some.
To allow for maximum size of the reading zone and minimal interference with clear distance viewing, the compromise with the new progressive designs is to shorten the mid-range zone, which is the part that is in focus at the usual distance of the CRT screen. Since the CRT screen is usually at eye level, it requires a head tilt back to put that mid-range focus zone in view of our eyes. We then get a combination that is less than optimal for some people.

Some suggestions to help are: 1. Back the monitor away and raise it up so the distance part of the lens can be used. 2. Lower the monitor so it is in view of the reading zone. 3. Consider a pair of computer glasses that have only midrange and near, or single vision near only. 4. Get a notebook computer, as these sit on the desk usually within the mid-range and near zone of the lens. 5. Consider line segment bifocals or trifocals.

The use of computers and a potential need for bifocals should be discussed with your doctor and/or your optician to maximize performance and comfort in this situation.

Q: What exactly is astigmatism? | Ask Dr. Chet

A: We see an object clearly when light from it or reflecting off it enters the eye and forms a focused image on the retina. Consider the simplest example of this, a point source of light like a star. If there is no astigmatism present, light entering the eye from the star will be focused forming an image that is also a point. (If the focused image forms in front of the retina, the eye is myopic or nearsighted. If it forms in back of the retina, the eye is hyperopic or farsighted. If it forms on the retina, there is no refractive error and the eye is said to be emmetropic.)

If there is astigmatism present, the light from the star will not focus as a point but instead will be distorted. (Actually, the image of the star focuses as two lines, one in front of the other and separated by some distance, with one line oriented 90 degrees from the other.) Don't bother trying to understand what astigmatism is. Just remember it distorts vision and can be corrected with special lenses called cylinders. The cornea having a shape that resembles a football instead of the normal case, a basketball, usually causes astigmatism. In most cases astigmatism occurs with either myopia or hyperopia. Some people have astigmatism only but not many. Astigmatism can be easily corrected with glasses, with rigid glass permeable contact lenses or with so-called "toric" soft contact lenses. "Toric" refers to the shape of one of the lens surfaces. It is the toric surface that is responsible for correcting the astigmatism.

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