William J. Benjamin, OD, PhD, contributing editor, University of Alabama at Birmingham School of Optometry/The Medical Center

Clinical R&D

"Super-Perm" or "Normo-Perm": What Risks Accompany

High Oxygen Permeability? '11" / oday ' s silicone-acrylate and fluo- ropolymer rigid lenses have given the practitioner opportunities to indi- vidually tailor contact lens materials to patients or modes of contact lens wear. However, "tailor-made" mate- rial selections for the patient are pretty much still obtained by the "trial and error" method, so that the prac- titioner will generally only prescribe one or two rigid lens materials for most of his patients. Beneficial qual- ities that may distinguish one mate- rial from another have become in- tangible, for instance, "functional wettability", "flexibility", "biocom- patibility", "optical quality", "stability", and "durability", to name just a few attributes of contact lenses.

Oxygen permeability, one of the few aspects of today's contact lens materials that is acceptably measur- able, is thought to be a positive attri- bute of any contact lens. And so, manufacturers and practitioners alike have tended to emphasize its impor- tance, if for no other reason, be- cause of the lack of other "tangible" lens factors which could spell the difference for a patient. Everyone knows that more oxygen is better, but in order to build oxygen perme-

ability into new contact lenses, sev- eral "intangibles" have had to be compromised. For extended wear, if deemed appropriate, the risk/benefit ratio of compromises may be per- missibly low for some patients. How- ever, highly oxygen-permeable rigid lenses (even the so-called "super perms") are recommended also for daily wear, to perhaps enhance cor- neal and reduce long-term changes,

i.e. endothelial pleomorphism, for most patients wearing rigid lenses.

High-Dk Rigid Lenses: Steep Fits May Induce Suction

Deleterious epithelial effects of rigid extended wear notwithstanding (peripheral ulcers, 1 central spot ero-

2 3 4 sions, central abrasions,' etc.), the use of "high-Dk" rigid lenses for

Figure 1: Grade 3 fluorescein staining of the central corneal epithelium of the right eye following removal of a steeply-fit (+0.5OD) Boston IV high-Dk rigid lens. The lens had been immobile, probably adherent to the cornea, previous to loosening by application of eye drops and removal by the patient. The epithelium healed rather slowly without contact lens wear, and was intact by slit-lamp examination four days after this photo was taken.

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daily wear has begun to bring in patients with an increasing, albeit lesser, incidence of similar complica- tions, s,6 If daily wear of high-Dk rigid lenses is to be pursued, the fitting and follow-up of such lenses will be- come less tolerable of error or ne- glect. Figures 1 and 2 show central staining in areas of about 3mm di- ameter on the right eye (Figure 1) and left eye (Figure 2) of a patient who had been fit with Boston IV lenses in a daily-wear mode, in my opinion about half of a diopter steeper than alignment in the right eye and slightly steeper than that in the left. The lenses had ceased to move upon the blink during daily wear, and were most likely adherent to the cor- nea before the patient removed the lenses.

The patient's corrected vision was reduced by 2 lines of acuity with and without contact lenses on. The epi- thelium in this case did not heal rapidly and the epithelial defects were evidently of the recurrent vari- ety, possibly due to the long-term nature of this epithelial trauma over months of contact lens wear. The right cornea healed in approximately 4 days without contact lens wear, but the left cornea (the epithelium of which was more severely injured-- see fluorescein in the stroma in Fig- ure 2) required nearly two weeks for the epithelium to become intact! Even then, while the spectacle acui- ties of the two eyes had reached an acceptable 20/20, keratometric cor- neal reflections were slightly dis- torted for the left eye.

In another incident, a daily wearer of SGP-II high-Dk lenses placed his contact lenses in the wrong eyes one morning. This produced a lens on the left eye which was approxi- mately half of a diopter steeper than alignment. Figure 3 shows the cen- tral staining that occurred after the immobile, probably adherent lens on the left eye was removed. Interest- ingly enough, the lens on the right eye moved well, although it was then slightly flat relative to the right cor- nea. This patient's cornea healed

Figure 2: Central corneal disruption revealed by Grade 4 fluorescein staining of the left eye of the same patient whose right eye is shown in Figure 1. The Boston IV lens had been fit slightly steeper for this eye than in the right eye. The epithelium was so affected here, that fluorescein quickly made it into the stroma, thus obscuring the actual epithelial lesions in this photograph. Affer four days without contact lens wear, this cornea looked approximately as did the right eye in Figure 1. Slowly, the epithelium healed and only became intact by slit lamp examination after two weeks. It is possible that the epithelium in both eyes, but particularly for the left eye, did not adhere properly or quickly to the stroma having undergone long-term trauma and therefore recurrently showed staining on successive days.

Figure 3: A wearer of SGP-II high-Dk oxygen-permeable rigid contact lenses switched his lenses one morning and inadvertently placed them in the wrong eyes. This created a lens/cornea litting relationship in the left eye that was +O.50D steeper than alignment, and the lens became immobile when it (probably) bound to the epithelium. The fluorescein staining pattern of the left eye is shown here. Fortunately, the epithelium had been traumatized for only a short time, therefore, the epithelium healed overnight.

the trauma endured by the corneal epithelium was of only short duration in this case.

In order to "enhance the oxygen", rigid lens polymers have attained qualities that allow them to adhere to the cornea, 1 sometimes even in daily-wear situations. 6 This causes problems for the practitioner and po- tential harm to the patient. 3,s The

lens that doesn't "stick". But until that is achieved, in practice I will tend to prescribe rigid lenses made of Iow-Dk or medium-Dk materials ("normo perms") for daily wear, admittedly perhaps neglecting the long-term corneal benefits of lots of oxygen, but avoiding more immediate and perhaps devastating epithelial com- plications of high-Dk rigid lenses rapidly and by the next day the epi-

thelium was intact, possibly because answer is, of course, a high-Dk rigid should the cornea become infected.

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Figure 4: Biomicroscopic photo with fluorescein from Benjamin and Boltz, 6 revealing arc-like "compression ring" due to an adherent Boston IV lens and resultant sterile ulceration found on a daily-wear patient. Because the corneal defects did not become infected, this cornea healed within several days and the patient did not sustain permanent eye damage.

References

1. Levi, B. Rigid Gas-Permeable Lenses for Extended-Wear A One-Year Clinical Evaluation. Am J Optom Physiol Opt 62(12): 889, 1985.

2, Benjamin, WJ. Learning From Aphakes. Rev Optom 122(4):49, 1985.

3. Pole, JJ. Corneal Abrasion Due to Lens Adhesion Phenomenon With Rigid Gas-Permeable Lens Ex- tended Wear. ICLC 14(12):493, 1987.

4. Benjamin, WJ and Simons, MH. Extended Wear of Oxygen-Perme- able Rigid Lenses in Aphakia. ICLC 11 (9):547, 1984.

5, Benjamin, WJ. Corneal Abrasions: Possible Etiology "of EW Ulcer- ations? ICLC 15(4): 134, 1988.

6, Benjamin, WJ and Boltz, RL. Pho- tographic Atlas: RGP Lens Adhe- sion is not a Benign Phenomenon; ICLC 16(2):61, 1989.

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