Lens Related Dry
Lens Related Dry
By Jordan Kassalow, OD,MPH,
Cary Hirschfield, FNAO, HFOAA, Richard S. Kattouf, OD, and
Richard S. Kattouf II, OD
The goal of any practitioner who fits contact lenses is to help his patients achieve good vision, good comfort and good health. Unfortunately, dry eye is one of those defined conditions that can render the best contact lens useless against mucous, aqueous or lipid deficiency.
Understanding Dry Eye
The ocular surface creates a deficient tear layer due to three defined factors. The first factor is the lipid layer, which is variable on the surface of a hydrogel lens and causes the surface of the lens to dehydrate according to the polymer characteristics. The second factor, which is typically extremely thin, is the amount of tear layer between the contact lens and the ocular surface. Evaporation develops, there is increased metabolism, which creates heat, and there is increased friction between the lens polymer and the ocular surface. The tear layer becomes variable from ocular surface irregularities, which provide poor tear adherence. These factors contribute to a patient's dry eye symptoms and to uncomfortable contact lens wear. Added to these factors is the third factor, creating tear evaporation through the use of computers, prolonged reading, automobile ventilation, air conditioners and low humidity, thereby promoting complaints of dry eye.
Dry Eye-Related Problems
As contact lens practitioners, we are constantly challenged to meet the needs of our dry eye patients. A growing problem that we face with these patients is properly defining, quantifying and resolving dry eye symptoms. Diagnosis is guesswork without the proper tools to define, quantify and qualify the condition. Practitioners apply lenses in a trial-and-error fashion, trying to find the one that satisfies the patient's definition of comfort. All hydrogel lenses lose water during their wearing cycle. Additionally, dehydration occurs when the temperature of a lens increases from room temperature to eye temperature. Lens design and polymer characteristics can have a major effect on the success or failure of the environmentally induced dry eye patient.
The goal of this study was to provide data comparing the Preference lens to the Proclear lens. The question we set out to answer: "Is the Preference polymer capable of promoting lens comfort for patients who experience environmentally induced dry eye? The Preference lens possesses those properties that would work well with defined dry eye patients. Low water content, good edge design, deposit resistance and frequent planned replacement are the optimal characteristics to promote comfortable lens wear.
This study included 18 well-adapted Proclear soft lens patients who were 18 years and older with a prescription between -1.00D and -4.00D with unremarkable ocular history. The study required patients to report for three office visits (dispensing, one-week follow-up and one-month follow-up). At the dispensing visit, each patient wore one Preference lens (test lens) and one Proclear lens (control lens) placed on the contralateral eye simultaneously. Each patient was asked to compare the two lenses for comfort, vision, dryness and handling, and the practitioners were asked to compare fitting characteristics. The lenses were then switched and a repeated evaluation was performed. Responses were recorded and lenses were dispensed. Patients used the same lens care system they had been using prior to the start of the evaluation. Patients were asked to compare the two lenses for comfort, fit and deposit resistance. Finally, each patient was asked to select a preferred lens.
Two practitioners tested nine subjects each. The subjects compared vision, comfort, dryness and handling, while the practitioners compared fit and deposit resistance between the test and the control lens.
Vision -- Ten of the 18 subjects (56%) reported superior vision with the Preference lens, seven (39%) reported their vision to be the same and one subject (6%) reported superior vision with the Proclear lens. Thus, vision with the Preference lens was preferred or equal to the Proclear lens 97 percent of the time.
Comfort -- The Preference lens was preferred by five patients (28%), and two patients (11%) found the Proclear lens to be more comfortable. Of the subject population, the Preference lens was ranked as being as comfortable or more comfortable than the Proclear lens 89 percent of the time. Comfort was reported as equal for each lens by 11 patients (61%).
Dryness -- The results of dryness between the Preference lens and the Proclear lens was reported equal by 13 patients (72%). The Preference lens was preferred by five patients (28%) with respect to dryness. Thus, 100 percent of the patients reported that the Preference lens was equal to or better than the Proclear lens with regard to dryness.
Handling -- The handling characteristics were determined by 10 patients (56%) to be equal between the Proclear lens and the Preference lens. Six patients (33%) preferred the Preference lens to be better with regard to handling. Two patients (11%) felt that the Proclear lens was superior with regard to handling. Of the total subject population, the Preference lens was equal to or better than the Proclear lens 89 percent of the time.
Fit and deposit resistance -- The investigators found no significant difference between the test and control lenses in the categories of fit and deposit resistance. This one-month evaluation was not long enough to sort out any significant differences between the two lens types. Future tests will have to be carried out for a longer duration to find out if there are any significant differences with respect to fit and deposit resistance. We can not rule out a placebo effect for the Preference lens.
Practitioners' wish to improve comfort and permeability with soft lens materials might include a high water content polymer. Because lens dehydration is often the culprit when patients complain of uncomfortable lenses, the obvious conclusion is that the more water content a soft contact lens has, the more comfortable it will be. High water content lenses may initially feel more comfortable, but as the lens dehydrates, the parameters change. Dehydration is an important factor to consider when selecting a polymer of first choice. A high water content lens that is exposed to ambient conditions loses water, thus resulting in a lower Dk value, lens parameter instability, less durability, poor handling characteristics and dry eye symptoms. As practitioners, we need to search for lens materials that bind strongly with water, creating a more stable lens polymer.
The Proclear lens represents this new era of enhanced polymers. The key component of omafilcon A is phosphorylcholine, which is responsible for maintaining surface and bulk dehydration. Using phosphorylcholine results in sustaining oxygen flow, moisture retention and deposit resistance. This comparison study evaluated the Preference lens to the Proclear lens, which has an indication for patients with dry eye discomfort. The investigators compared these two lens materials and designs to discover if the Preference lens, made of tetrafilcon, is substantially equivalent to the Proclear polymer and design.
The tetrafilcon material is a 42.5% low water nonionic lens polymer. The characteristics of this lens material are low dehydration and deposit resistance. The FDA governs the indicated use of a lens polymer, which is stated in its labeling section on the package insert, in addition to any marketing materials. Practitioners are able to use any device they deem appropriate to solve a patient's health-related problem. In order to receive a change in labeling description, a well-controlled FDA regulated investigation must be performed.
Although artificial tears and lens lubricants temporarily relieve dry eye symptoms, they need to be used frequently throughout the day due to their rapid drainage through the lacrimal system. This inconvenience creates a loss of enthusiasm among contact lens wearers. Punctal plugs can provide some relief, but again, this procedure can provide another barrier to successful contact lens wear. A lens polymer that reduces dry eye sensation is still the best remedy for patients who are experiencing discomfort and reduced wearing time.
Only one patient (6%) out of the 18 tested preferred vision through the Proclear lens. Two patients (11%) preferred the comfort of the Proclear lens. No patients reported that the Proclear lens provided less dry eye symptoms than the Preference lens. The Proclear lens was favored by two patients (11%) out of the 18 with regard to ease of handling. This small sample size suggests that the Preference lens, Group I nonionic low water content lens, would be an option for the practitioner to select when fitting patients with dry eye symptoms in addition to the nonionic Proclear lens polymer. Practitioners now may have a choice of a high water content Group II or a low water content Group I nonionic lens to address mild discomfort or dry eye symptoms.
Patients challenge practitioners to resolve their dry eye symptoms while wearing contact lenses. The problems in developing lens materials, designs or modalities that resolve dry eye symptoms resides in the patient's subjective assessment. Contact lenses increase tear evaporation loss five to eight percent, and hence, stress the tear layer. As the water content of a lens polymer increases, this has a magnified effect. The ability to coat a lens with tear lipids when it is placed on the eye will determine lens evaporation. All contact lenses disrupt tear film and result in reduced tear break-up time after a few hours. Finding a lens that retards on-eye dehydration will have an effect on post-lens tear film depletion. The Proclear lens was approved by the FDA, labeled with the claim "may provide improved comfort for contact lens wearers who experience mild discomfort or symptoms related to dryness." In this two-investigator field study evaluation, the Cooper Preference lens performed equal to or better than the Proclear Compatibles lens in most cases with regard to dryness, comfort, vision and ease of handling.
This study was sponsored by CooperVision.
Dr. Kassalow is a partner at Drs.
Kassalow and Resnick, ODPC in Manhattan and in Rosyln, Long Island. He specializes in hard-to-fit contact lens cases and laser vision correction. He is also an adjunct senior fellow for Global Health Policy at the Council on Foreign Relations, and a board member at Lighthouse International.
Mr. Hirschfield has been in practice with Drs. Farkas, Kassalow and Resnick since 1989. He is an honored fellow of the Opticians Association of America and a fellow of the National Academy of Opticianry.
Dr. Kattouf is in private practice in Warren, Ohio, and is president and founder of two management and consulting companies.
Dr. Kattouf II specializes in orthokeratology, low vision and pediatric optometry. He is a member of the American Optometric Association.
Contact Lens Spectrum, Issue: March 2000