International Ophthalmology 16: 123-127, 1992. �9 1992 Kluwer Academic Publishers. Printed in the Netherlands.

Extended-wear of high oxygen-permeable quantum contact lenses

J.H.C. Kok, H.J. Hilbrink, R.M. Rosenbrand & R. Visser Academic Medical Center, Cornea and Contact Lens Unit, Department of Ophthalmology, Amsterdam, The Netherlands

Accepted 4 November 1991

Key words: contact lens, high gas permeability, permanent wear

Abstract

This study was performed to investigate the effects of extended-wear of rigid aspherical high gas-permeable contact lenses on the cornea. In the study 32 subjects (62 eyes) were followed over a period of 3 to 24 months. A high gas-permeable contact lens (Dk 92), made of fluoro-silicone-acrylate copolymer, was used. Vision remained constant during the studied period. The corneal thickness decreased significantly (p < 0.05) during the first six months. Significant changes (p < 0.05) were found after three months in the corneal curvature, especially in the vertical meridian. No further topographical changes were noted in the period between three and six months of extended-wear. Complications, like acute red eye syndrome and bacterial infections, which may be encountered in soft lens extended-wear, were not noticed. At the end of the study 20 subjects (38 eyes, 61%) were still on extended-wear, 9 subjects (18 eyes, 29%) changed to daily wear and 3 subjects (six eyes, 10%) became unavailable for follow-up. Extended-wear of rigid aspherical high gas-permeable contact lenses may be considered as an acceptable alternative for soft lens extended-wear.

Introduction

In several studies researchers found clinical limita- tions to the extended-wear of soft contact lenses, for instance disturbances of corneal metabolism, morphological changes (polymegathism), bacterial and fungal infections, staining of the cornea and impaired or insufficient vision (1-4). The devel- opment of rigid high gas-permeable materials seems to be very promising, giving the patient the possibility of extended-wear without the high num- ber of complications found in extended-wear of soft contact lenses. This is based on a better oxygen supply of the cornea by rigid high gas-permeable lenses than by soft lenses (5). Furthermore, a rigid lens has a warning nature. In case of a corneal complication the lens will cause so much pain that the patient will immediately remove the lens. A

soft lens has a bandage effect and for this reason it may mask corneal complications. The patient will consult an eye specialist in a later stage than the case in rigid lens wear.

A further improvement in rigid contact lens wear is the introduction of an aspherical lens design, consisting of a contact lens surface which runs in alignment with the corneal topography. This helps to make the lens comfortable under daily wear conditions (6).

The Quantum lens was chosen for this project for the reason that it was the first high Dk aspherical rigid lens, commercially available on the European market.

The purpose of this study was to determine the complication rate of long-term extended-wear of rigid aspherical high gas-permeable contact lenses. The long-term clinical effects on corneal thickness

124 J.H.C. K o k et al.

0.54

0 . 4 9

0.48 I I I t 0 3 6 12 24

time ( m o n t h s )

Fig. 1. Corneal thickness change (mm) during extended-wear of rigid gas-permeable lenses.

and the horizontal and vertical meridians were fol- lowed. The assessment of the endothelial cell mor- phology is presented in another publication (7). Also, the success rate over a long period of perma- nent wearing of rigid lenses, which can be ex- pressed in the number of drop outs, was noted.

Materials and Methods

The lens material properties are shown in Table 1. The lens used has a sphero-elliptic design. The lens has a spherical optical zone with an aperture of 14 degrees from the optical axis. The lens flattens progressively towards the periphery, without junc- tion zones. An aspherical flattening, according to a curvature with an eccentricity (E) of 0.6, is manu- factured by computer-guided machinery. The lens is produced by Bausch and Lomb, Ireland, and marketed as Quantum 92.

Thirty-two consecutive subjects, (18 females and 14 males, 62 eyes) with an average age of 33.2 years, s.d. 7.4 years, range 24-57 years were fitted. Sixty eyes were myopic, 2 hyperopic. The spherical correction, spherical equivalent, ranged from + 5 to - 17.5 diopters with an average of - 5.0 D, s.d. 4.1 D. The mean central corneal astigmatism had a range from 0 to 3 diopters with an average of 0.72 D, s.d. 0.62 D. The total lens diameter was 9.30

mm for 5 eyes, 9.60 mm for 47 eyes and 10.20 mm for 10 eyes. Of the extended-wear subjects in the study five were previous soft lens wearers and 22 had used a rigid PMMA or a first generation low gas-permeable rigid lens. Five had no previous con- tact lens history.

Not all subjects entered this study at the same time. One subject was followed for three months (2 eyes), 12 subjects for six months (23 eyes), 3 sub- jects for one year (5 eyes) and 16 subjects for two years (32 eyes). Each patient was free to finish the extended-wear program when he chose.

The lenses were removed for cleaning and exam- ination only. The following clinical parameters were recorded during the study: visual acuity, pa- chymetry, keratometry and slit-lamp findings.

The corneal thickness was determined with a pachymeter modified according to Mishima (8) and mounted on Haag-Streit slit-lamp in combination with fixation lamps. To facilitate precise measure- ments, the tear layer was stained with fluorescein. All measurements were taken within two to four hours after awakening. The corneal curvature was assessed on the basis of two central K-readings. The flattest corneal meridian served as a starting point for the selection of the base curve radius of the contact lens. In cases with an astigmatism over 1.5 D the base curve radius of the contact lens was decreased according to the amount of astigmatism. The fitting was checked with the use of fluorescein. An optimal fit was considered to have good lens centration and movement. In addition the lens should exhibit alignment with the corneal topo- graphy. This was controlled by examination of the fluorescein pattern of the tears under the lens. An

Table 1. Properties of Quantum 92 contact lens material

Lens material Fluoro-silicone/acrylate copolymer (Siflufocon A)

Oxygen permeability

Hardness Wetting angle Refractive index

92 x 10 -11 cm ml 02/sec Fatt method (35 ~ ) 114.6 Rockwel R scale or Shore D81 24 1.43 at 25 ~ dry

even distribution of the fluorescein without dark oppressive zones was required.

For statistical analysis a Mann-Whitney U-Test was used.

The study was approved by the Medical Ethical Committee of the Academic Medical Center. In- formed consent was given by each subject.

Results

In the course of this study there were three drop- outs: two lost for follow-up due to change of ad- dress, one because of protocol noncompliance (a total of 6 eyes). Seven subjects preferred using the lenses on a daily wear basis because of discomfort or personal reasons (a total of 14 eyes). One subject was withdrawn from the study in an early phase on the basis of the evaluation of endothelial photo- graphs. The poor state of the endothelium was probably related to previous PMMA contact lens wear (a total of 2 eyes). One subject switched to daily wear because of lens binding (a total of 2 eyes). The maximum follow-up time was two years. Thus at the end of the study 20 subjects (38 eyes , 61%) were still wearing the lenses on an extended,wear basis.

Visual acuity remained unaltered in all patients during the study period (data not shown).

There were no significant changes in corneal thickness in the first three months (Fig. 1). Extend- ed-wear for longer periods (6-24 months), how- ever, did induce a significant (p < 0.05) decrease in corneal thickness compared to the initial values at the beginning of the study. The most important decrease in corneal thickness occurred in between three and six months, whereafter the corneal thick- ness remained stable.

The vertical central corneal radius (Fig. 2) showed a significant (p < 0.05) flattening in the

Table 2. Positive slit-lamp findings ( N = 32 eyes).

Staining (mild) 8 (25%) Microcysts (< 10) 3 (9%) Dimpling 2 (6%) Lens Binding 1 (3%)

Extended-wear of contact lenses 125

800

E g .2 "o

F o (J

2

795

790

785

780

775 c

770 0

I I I I

3 6 12 24 time (months)

Fig. 2. Horizontal and vertical keratometer readings during extended-wear of rigid gas-permeable lenses, horizontal, verti- cal

first three months. The horizontal central corneal radius also showed a flattening, which was not statistically significant. After six months of lens wear both the horizontal and vertical K-readings did not change any more.

Few positive slit-lamp findings were assessed (Table 2). One subject was dismissed from the study due to lens binding and one due to the poor state of the endothelium. Both switched to success- ful daily wear.

Discussion

In 1989 excellent tolerance, lack of adverse reac- tions and stable visual acuity were reported in a daily wear study of a new rigid gas-permeable as- pherical lens (Quantum) (6). In this study the clin- ical consequences of extended-wear of the same lens were assessed. Despite the decrease in corneal thickness and the flattening of the horizontal and vertical central cor- neal radii, no impairment of visual acuity was ob- served. A change of the base curve radius of the cornea is probably compensated by the tear layer under the contact lens. Therefore the total refrac- tion of the combination of the contact lens, the tear layer and the cornea does not change. Consequent- ly visual acuity is of no use as a follow-up parameter

126 J.H.C. K o k et al.

in an extended-wear study. Lenses should be re- moved and K-readings should be measured at each follow-up visit to assess alterations in central cor- neal curvature.

This study showed a decrease in corneal thick- ness after six months extended-wear of rigid as- pherical high gas-permeable contact lenses. In a similar study, using aspherical lenses with compa- rable oxygen permeability, no statistically signif- icant changes in corneal thickness were reported (9). However, the mean value of the corneal thick- ness in the beginning of the latter study was lower than in this study and comparable other studies (10,11). A difference in contact lens history prior to entrance of the study may have influenced the mean value for corneal thickness in the beginning of the study and the subsequent reaction in extend- ed lens wear.

A decrease in corneal thickness, mainly caused by stromal thinning, despite chronic corneal ede- ma, has already been reported earlier by Holden (1) in subjects wearing soft contact lenses. A specif- ic reason for this phenomenon has not yet been found but a possible reason is a contact lens-in- duced change in the composition of the corneal stroma (12). The same factor which causes corneal thinning in soft contact lens wear may result in the change in corneal thickness with the rigid gas-per- meable extended-wear of rigid gas-permeable lens- es in our study.

Our findings of central corneal flattening con- firm the results of a similar study, using comparable aspherical high gas-permeable rigid lenses on ex- tended-wear basis (9). Corneal topography chang- es after contact lens wear can at least have two causes, an unevenly distributed corneal thickness change, or a mechanical molding of the shape (13). For instance, central corneal edema in rigid gas- permeable contact lens wear may be related to steepening of the central corneal curvature (14). In our study the corneal base curve radius flattened statistically significantly within the first three months. The thinning of the cornea, however, be- came significant after three months. It is very un- likely that there is any relation between these two parameters in our study.

Without an increase in thickness of the cornea,

the corneal curvature will mold in the direction of the fit of the lens (13,15). In our study the base curve radius of the lens is chosen according to the flattest of the two central corneal keratometer readings, which is usually the horizontal. It follows that the change of the vertical keratometer reading is larger than the horizontal change in an approach to the curvature of the contact lens. A possible connection between flattening of the horizontal and vertical meridian might explain why the hori- zontal meridian becomes flatter.

Irregular, and generally increasing, astigmatism has been a long-term side-effect of rigid PMMA contact lens wear (15-17). The keratometer images in our study, however, have not been irregular or distorted and no progress in astigmatism was re- corded during a follow-up time of two years.

Only a few positive slit-lamp findings were re- corded during the study. The single case of lens binding was found in a subject who previously had worn PMMA rigid contact lenses for 15 years on a daily wear basis. This had changed the shape of her cornea to such an extent that inevitable high-riding of the lens was induced. The lens binding, and consequently the switch to daily wear, therefore, relates mainly to previous contact lens wear. One subject with a poor state of the endothelium, as assessed by endothelial specular photography, was excluded for further extended-wear in the begin- ning of the study for safety reasons. Other compli- cations like punctate staining, microcysts and dim- piing never necessitated exclusion from the study. In contrast with soft lens extended-wear studies (2,3), no ulcerative keratitis was found in our study.

The percentage of success in an extended-wear study may be influenced by personal motives, com- fort and complication rate. A reserved attitude towards the phenomenon of extended-wear exists in Europe compared with the United States and Australia. At the end of the study 20 subjects (38 eyes - 61%) were tolerant and motivated for ex- tended-wear. This percentage is somewhat lower than the 70% success rate of the CCLRU study (18). Nine subjects (18 eyes - 29%) switched to a daily wear schedule after at least six months of extended-wear. It was not clear whether this was

more re la ted to discomfort or lack of mot iva t ion

for ex tended-wear . However , apar t f rom min imal

corneal s ta ining no obvious reason to d i scont inue

ex tended-wear was found.

In the past, ex tended or con t inuous soft and rigid

contact lens wear has been l imited in Eu rope , prob-

ably due to the emphasis which is put on safety and

side effects. The prerequis i tes for safe ex tended-

wear have b e e n ou t l ined in the l i tera ture (5,19).

Ex t ended -wea r of rigid high gas-permeable contact

lenses may be cons idered as an acceptable a l terna-

tive for soft lens ex tended-wear . Such side-effects

as discomfort , lens b ind ing , changes in corneal

shape and s ta ining of the ep i the l ium need careful

mon i to r ing and long- te rm follow-up. They main ly

relate to the fi t t ing re la t ionship of the cornea and

the contact lens. D e v e l o p m e n t s in the knowledge

of corneal topography and lens design may help to

improve ex tended-wear of rigid lenses in the fu-

ture.

Acknowledgement

We thank Professor Dr. A. Ki j ls t ra for his suppor t

and advice in p repar ing this article.

References

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Extended-wear of contact lenses 127

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Address for offprints: J.H.C. Kok Academic Medical Center, Cornea and Contact Lens Unit, Department of Ophthalmology A2-130, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands