Comfort, Convenience and Acuity Understanding Factors Leading to Contact Lens Success

BY JOEL A. SILBERT, O.D., F.A.A.O.
SEPT. 1996

But even the planned replacement proponents still must decide whether to use high or low water lenses, thin or ultrathin, visitint or enhancement tint. And then we must choose a replacement schedule that can vary from quarterly to as short as one day!

Despite the merits of planned replacement, now and then we should remind ourselves of the basics.

BACK TO BASICS

If you can't make a lens comfortable, it doesn't matter how sharp the vision is or how much oxygen you're sending to the cornea. Our patients want COMFORT more than anything else. How else can we explain why so many people in this country wear soft lenses. To achieve comfort, remember these basic tenets:

1. Use a lens design that fully covers the cornea, overlapping the limbus 360 degrees. The lens should have a good edge that does not cause mechanical trauma.

2. The lens should move -- not a lot, but not too little -- about 0.5mm for ultrathin, disposable lenses and about 1.0mm for thicker, conventional lenses. The lens should move freely with the blink and in up-gaze. If in doubt, use your finger to nudge the lens with the patient's lower lid to see if it has some free, gliding movement. (No, conjunctival 'drag' doesn't count!) Remember, too, that a tight-fitting lens may initially feel very comfortable, yet after several days, comfort declines as physiological problems develop.

3. Finally, good comfort depends not only on short-term requirements, but also on long-term corneal health. While many individuals wear lenses on an extended wear basis, more and more practitioners are starting to realize the risks inherent with this modality, and the benefits of comfort, good vision and outstanding eye health with planned replacement daily wear. Daily wear lenses, whether prescribed as planned replacement or conventional modalities and regardless of water content, do meet the physiological needs of the cornea for most patients. This is not the case, however, when patients wear hydrogels on an extended wear basis.

OPTIMIZING O(2)

Even with daily wear lenses, our patients may not achieve long-term comfort because HEMA-based hydrogel polymers are so prone to losing water. This may occur through evaporation on the anterior lens surface, pervaporation through the lens or from competition for tears from marginally dry eyes. If high water content were the answer, we'd all be using lenses that are 70+ percent water. This obviously is not the case. Orsborn (1988) showed us that high water, thin hydrogel lenses, theoretically the most oxygen transmissive combination, can cause significant desiccation, corneal staining and dry eye symptoms after just a few hours of wear.

Andrasko showed us that the use of lower water, thicker hydrogels slows the rate of water loss. Thus, for the patient with marginal dry eye, prescribing an ultrathin conventional lens or a thin disposable lens may not be 'just what the doctor ordered.' A low or mid water content lens (less than 60% water) that is not so thin as to cause desiccation, but thin enough to allow good oxygen transfer is today's optimal lens for all-day comfort.

Patients' tear quality and quantity vary greatly, as do their work and play environments. HEMA-based hydrogel lenses may perform well for some, yet fail miserably for others.

Remembering the basics will help us narrow the field and select a suitable lens. For some, this may be a planned replacement disposable lens. For others, the conventional lens may be the best choice. And for a certain subgroup, no HEMA-based lens polymer or design will do, and an RGP lens or a non-HEMA lens material will be the answer.

Good vision with soft contact lenses contributes to ultimate patient comfort and satisfaction. It results from good optics, good surfaces and good wettability with minimal deposits; it suffers when lenses dehydrate. Front surface tear thinning or tear break-up should significantly exceed the interblink period. Good vision also depends on a good fit. And a lens that resists deposits or that stays clean reduces patient dependence on lubricating/rewetting drops, which also improves patient convenience.

MINIMIZING DEPOSITS

No discussion of contact lens comfort and convenience would be complete without a few words about minimizing deposits. We know that hydrogels with higher fluid content and ionically charged surfaces are the most likely to attract deposits. Deposited lenses can certainly reduce comfort and compromise vision and long-term eye health.

Again, the basics remind us that there are two approaches to minimizing deposits: either dispose of lenses frequently, or use a lens that resists deposits. Until someone develops the perfect soft contact lens, a lens which will neither dry out nor develop deposits, these fundamental approaches will enable you to help your patients achieve higher degrees of success. CLS

Dr. Silbert is director of the Cornea & Specialty Contact Lens Service at The Eye Institute of Pennsylvania College of Optometry in Philadelphia.