LENS COMPARISON
A Comparison of Two Planned Replacement Contact Lenses
This practitioner fit his patients with two different planned replacement lenses to assess comfort, clarity and handling.
By D. L. Mormon, OD

In my May 1998 Contact Lens Spectrum article, "Validating Clinical Beliefs: A Disposable Lens Comparison," I compared Biomedics 55 UV to the other available spherical disposable/ planned replacement soft contact lenses for 289 patients. Because I have had such great success fitting the Biomedics 55 UV lens these past few years, I became intrigued when Ocular Sciences introduced the Hydrogenics 60 UV lens, with the assurance that it would meet or beat all the expectations and success which I had experienced with the Biomedics 55 UV lenses.

The primary difference between Biomedics 55 UV and Hydrogenics 60 UV is the lens material. Biomedics 55 UV is made of ocufilcon D, which has a 55 percent water content, whereas Hydrogenics 60 UV is manufactured with ocufilcon F, which has a 60 percent water content. This results in a 23 percent increase in Dk/L with Hydrogenics 60 UV lens compared to Biomedics 55 UV, which represents a significant increase in oxygen transmissability for those patients requiring more oxygen at the cornea and for those patients wearing their contact lenses on an extended wear basis.

The Hydrogenics 60 UV lens is manufactured by a dry cast molding procedure in ocufilcon F material. The lens has a sagittal depth of 3.75mm (8.5mm base curve.), 14.1mm diameter, Dk/L of 34.7 (at ­3.00D), UV monomer and center thickness of 0.07mm (at ­3.00D). The Hydrogenics 60 UV lens is similar to the Biomedics 55 UV in lens design, which is based on a low edge apex, CN bevel and a lenticular carrier design which ensures optimal comfort and handling. Biomedics 55 UV has a 8.6mm base curve, 14.2mm diameter, Dk/L of 28.2 (at ­3.00D) and a center thickness of 0.07mm.

In order to determine if patients preferred Hydrogenics 60 UV over Biomedics 55 UV, I randomly fit one myopic eye with one lens and the other myopic eye with its counterpart. The design was a double-blind study on patients who were either new contact lens wearers or those who currently were wearing Biomedics 55 UV or other brands of soft lenses. The lenses were allowed to equilibrate for approximately 15 to 20 minutes before assessment.

Subjects assessed the initial comfort, handling and clarity of each lens. In cases where a significant difference in clarity or comfort was appreciated (after 20 minutes), the lens which was causing the discomfort or lack of clarity was discarded, and this eye was dispensed a lens matching the fellow eye. In all cases, this solved the comfort or clarity problem. In cases where clarity and/or comfort were comparable (both were acceptable), the two different lenses were dispensed. All lenses were worn on a daily wear regimen with a one-week follow-up evaluation.

On the follow-up evaluation, the lenses were again evaluated for comfort, clarity and handling. Whichever lens provided the greatest comfort and clarity was dispensed in three- or six-month supplies. Because handling was not a consideration for either lens type, this factor did not affect which lens was initially dispensed on the fitting or on the one week progress evaluation. Slit lamp assessment involving centration, lens movement and practitioner assessment of lens performance showed no significant differences. Objective assessment of auto-refraction and keratometer mire appearance with lenses in place, likewise showed no significant variations.

Subject Groups

Three different classifications differentiated the performance of Biomedics 55 UV vs. Hydrogenics 60 UV soft contact lens wearers. Group I consisted of new contact lens wearers, Group II consisted of current Biomedics 55 UV wearers and Group III consisted of current soft contact lens wearers of other contact lens materials. This grouping seemed logical because I wanted to assess:

• Which lens was more successful in fitting new contact lens wearers
• How Hydrogenics 60 UV compared to the currently successful Biomedics 55 UV contact lens wearers
• Which lens was a better refit for the other prior soft contact lens wearers

None of the patients in the various groups manifested a significant astigmatism which would predispose them for astigmatic contact lens modalities.

The entire contact lens wearing group consisted of 387 new and current contact lens wearers. Some 214 females and 173 males comprised the gender groups (Table 1). Some 158 (41 percent) patients preferred the comfort of Biomedics 55 UV, 199 (51.5 percent) preferred the comfort of Hydrogenics 60 UV and 30 (7.5 percent) patients showed no comfort preference for either of the two lens materials (Table 2).

Some 89 of the total group of 387 demonstrated a clarity/visual acuity preference. Thirty-four (38 percent) patients had clearer vision with Biomedics 55 UV. Fifty-five (62 percent) patients indicated sharper visual acuity with Hydrogenics 60 UV. The 55 patients (62 percent) who preferred the clarity of Hydrogenics 60 UV had a mean refractive error of ­3.06D, whereas the 34 (38 percent) patients who preferred the acuity with Biomedics 55 UV had a mean refractive error of ­2.51D (Table 3).

The 79 new wearers (Group I) consisted of 33 females and 46 males (Table 4). Some 32 (40 percent) patients preferred the comfort of Biomedics 55 UV and 45 (57 percent) preferred the comfort of Hydrogenics 60 UV. Two new contact lens wearers indicated no comfort preference. Within this group of new contact lens wearers, 20 females preferred Hydrogenics 60 UV, and 12 females preferred the comfort of Biomedics 55 UV. In the male group of new contact lens wearers, 20 patients preferred Biomedics 55 UV , whereas 25 patients showed an affinity for Hydrogenics 60 UV .

The 110 (60 percent) to 84 (40 percent) preference for Hydrogenics 60 UV lenses for the current Biomedics 55 UV lens wearers indicates a slight preference for switching Biomedics 55 UV wearers to the Hydrogenics 60 UV lens based on improved comfort in contact lens wear.

Some 99 patients in Group III (59 females and 40 males) were currently wearing other brands of soft contact lenses (Table 6). Forty-two patients (42 percent) preferred the comfort of Biomedics 55 UV lenses. Forty-four patients (44 percent) chose the comfort of Hydrogenics 60 UV lenses. Thirteen patients (14 percent) showed no preference for either Biomedics 55 UV or Hydrogenics 60 UV lenses. Patients in this group with higher refractive error generally preferred Hydrogenics 60 UV lenses compared to those with lower refractive errors who preferred Biomedics 55 UV lenses.

This clinical study of 387 contact lens wearers demonstrates from comfort preferences that 199 patients (51.5 percent) preferred Hydrogenics 60 UV lenses, whereas 158 patients (41 percent) preferred Biomedics 55 UV lenses. Some 30 patients (7.5 percent) demonstrated no preference. Those preferring the Hydrogenics 60 UV lens had a higher mean refractive error (­2.93D) compared to the ­2.55D mean refractive error of the Biomedics 55 UV lens. I deduce that higher myopes are likely to be more comfortable with slightly higher water/ higher Dk lenses, whereas lower myopes may be more comfortable with moderate water/ moderate Dk lenses.

Visual acuity appeared to be a significant factor in 89 of the 387 patients, which indicates that this is still an important factor in fitting either Biomedics 55 UV or Hydrogenics 60 UV. Some 34 (38 percent) of patients had clearer vision with Biomedics 55 UV, and 55 (62 percent) preferred the clarity of Hydrogenics 60 UV. Those who preferred the visual acuity of Hydrogenics 60 UV demonstrated a higher mean refractive error compared to those wearing Biomedics 55 UV. This might suggest that water content or Dk value might have an influence on visual acuity.

Because I cannot predict which lens a patient will prefer, I am continuing to trial fit Biomedics 55 UV on one eye and Hydrogenics 60 UV on the other. Since both lenses provide excellent handling, I am dispensing the lens which provides the better comfort and clarity. This procedure ensures that my patients receive the better lens as well as assure them that I always try to improve their vision, comfort and clarity by demonstrating new contact lenses as they become available.

Dr. Mormon maintains a full-time private practice in Germantown, Tenn., which specializes in contact lenses. He is also a tenured professor at the Southern College of Optometry and received his Doctor of Optometry degree from the University of Indiana.