Contact Lens Design & Materials
Better Vision With Contact Lenses
By Ronald K. Watanabe, OD, FAAO
Vision with contact lenses is sometimes taken for granted. We know contact lenses offer many advantages over spectacles, including a full field of vision, less chance that they will fall off or get damaged and superior self-perception through improved cosmesis. They are great for many activities, including sports, travel and work, and they are excellent options for both children and adults. Because most patients fall within the bell curve of normal eyes, contact lenses are also easy to fit in most cases. Yet, suboptimal vision is often accepted to keep the fitting short and simple. For example, the most common type of contact lens prescribed for a refractive error of –3.00 –0.75 x 180 is probably a spherical soft contact lens, because it is easy to fit and provides vision that is “good enough.” Yet, how often are spherical-powered spectacle lenses prescribed for such a patient? With today's advanced contact lens designs, it is easier than ever to provide better visual options for our patients, whether they wear soft or GP lenses.
Soft Lens Advances
Manufacturers can now design soft lenses—both spherical and toric—to correct spherical aberrations, so that the topic of higherorder aberrations has become a routine part of our discussions with patients about their vision. When fitted to a patient with an average amount of naturally occurring spherical aberration, these lenses provide improved visual quality, particularly in lowlight conditions.
I have found that most patients fitted with this type of lens design notice improved vision, even if they had no complaints about their vision previously. Asking a patient about his vision at night or in other low-light environments will help you determine if he may benefit from these designs. Be aware, however, that a patient who has an atypical aberration profile may not see an improvement in vision and may, in fact, report worse vision.
More Comfortable GP Lenses
GP contact lenses deliver better vision than soft lenses in most cases, mainly because:
1. Their rigid optics do not wrinkle or warp as easily as those of soft lenses.
2. They correct corneal astigmatism without the need for a toric design.
3. They reduce higher-order aberrations better than soft lenses (Hong, 2001; Dorronsoro, 2003).
Even though most patients would have clearer vision with GP lenses, they are often not prescribed because patients do not want to go through the necessary adaptation or because practitioners do not want to make their patients uncomfortable.
GP lens technology has improved considerably, however, enabling patients to enjoy sharper vision without the constant awareness of small-diameter lenses. Hyper-Dk materials can be manufactured thin, with precise curves and edge configurations that help initial comfort, and labs can make large-diameter designs that are more stable and easier to adapt to.
Newer, redesigned hybrid lenses made of hyper-Dk materials can provide the vision of GPs with improved comfort, compared to previous hybrid designs. For patients who want clear vision with better initial comfort, these new hybrids may be a good choice.
What's Best for Your Patient?
We are fortunate to have many excellent vision-correction options. Matching the best lens to your patient requires knowledge of these new products, acute evaluation of the patient's eyes and needs and a focused discussion with the patient. We can look forward to more advanced technology and better products as the knowledge base increases in the area of vision correction with contact lenses. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #194.
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a diplomate in the American Academy of Optometry's Section on Cornea and Contact Lenses and Refractive Technologies, and he is in private practice in Andover, Mass. You can reach him at email@example.com.