Contact Lens and Anterior Eye, Vol. 21, No. 3, pp. 85-88, 1998 © 1998 British Contact Lens Association Printed in Great Britain

A NEW RIGID GAS-PERMEABLE SEMI-SCLERAL CONTACT LENS FOR TREATMENT OF CORNEAL SURFACE DISORDERS

Willem Vreugdenhil *, Annette J.M. Geerards~ and Charles J.W. Vervaet* (Received 7th January 1998; in revised form 2nd April 1998)

Abstract - - Some extreme corneal irregularities cannot be treated adequately with corneal contact lenses. For such cases a rigid semi-scleral lens can be prescribed. We evaluated the use of a highly gas-permeable rigid semi-scleral lens in patients with diseased

corneas for whom conventional contact lens strategies had failed. Twenty two patients (29 eyes) were successfully fitted with individually manufactured semi-scleral lenses. Corneal hypoxia, which has previously limited the use of polymethylmethacrylate

(PMMA) scleral contact lenses, did not occur. The semi-scleral lenses were well tolerated. Two cases were selected to illustrate the fitting of these lenses.

KEY WORDS: rigid gas-permeable semi-scleral contact lens, ~ corneal surface disorders, keratoconus, keratoplasty

Introduction

S evere corneal distortion, which occurs in keratoco- nus and other corneal diseases, is a major obstacle

to the fitting of corneal contact lenses. 1 Inability to fit contact lenses is often due to a variations in the corneal bearing areas which make it impossible to achieve a satisfactory fit and can also result in subjective irritation. It is possible to use the 'Piggy Back' system in which a rigid corneal lens is fitted onto a soft lens, or to fit a SoftPerm ® (Sola/Barnes-Hind) lens in order to improve subjective complaints and to diminish ilTitationY

Since the bearing area of scleral lenses is scleral, a good fit can be achieved in most cases. Fick fitted lenses with a scleral or haptic design that were made of glass 4 and Feinboom ~ introduced scleral lenses with a plastics scleral zone to overcome some of the technical difficulties associated with the manufacture of glass lenses. Extensive use of these lenses was, however, limited by a short wearing time which was due to severe corneal hypoxia resulting in corneal oedema.

The use of gas-permeable materials in a scleral design was first described by Ezekiel, who reported the successful rehabilitation of patients with keratoconus, aphakia, severe myopia, and corneal scarring with f e n e s t r a t e d , g a s - p e r m e a b l e sc le ra l l e n s e s (Dk 16 × 10 -~) (cm~/sec) (ml Q m l × mm Hg) at 36°C. s However, these lenses had low oxygen permeability. Successful fitting of high gas-permeability scleral lenses, made of rigid fluoro-silicone acrylate coplymer with a Dk of 110 × 10 -11 (cm2/sec) (ml O2/ml × mm Hg) at 35°C, was reported by Schein et al. and Kok et al. 7,8

Significant advances in rigid gas-permeable materials have occurred over the past 10 years, encouraging further consideration of their application to a scleral design in the rehabilitation of diseased corneas. 9,1°

*Optometrist, Oculenti Contact lens Practice, Rotterdam. tOphthalmologist, The Rotterdam Eye Hospital, Cornea and Contact Lens Department.

Materials and methods A total of 29 eyes (22 patients) were fitted with a new rigid gas-permeable (RGP) semi-scleral contact lens; 14 patients were males and nine were females. The mean age was 42 years (SD 11.5 years; range 15 -75 years). The mean follow up was 7.3 months (SD 3.8 months; range 1 - 1 5 months) . T h e r e were 18 eyes with ketatoconus, five eyes with keratoplasty after keratoco- nus, four eyes with a keratoplasty after corneal dystrophy and two eyes with a keratoplasty following a corneal ulcer. All these patients had previously at- tempted to wear other forms of contact lens without success before they were fitted with semi-scleral lenses. The cases included 22 eyes fitted with rigid lenses, one eye fitted with a 'Piggy Back' system, three eyes corrected with spectacles due to intolerance of contact lens wear, and two eyes fitted with PMMA scleral lenses. The main goals in fitting semi-scleral contact lenses were to achieve better tolerance and visual rehabilitation.

The material Used was a fluoro-silicone acrylate copolymer with a high oxygen permeability (Dk 120). A button of this material was machined to the patient's specification using Sub Micron Lathe cut (SML) technology which is said to have an accuracy of 0.001 ram. Reproducibility is claimed to be 100% and polishing is unnecessary.

The semi-scleral lens has an optic zone comprised of three aspheric curves and a mono-curve scleral zone. The lens has a multi-curve front surface design with a front optic zone diameter of 8.50 ram. The front peripheral radii maintain a thickness of 0.40 mm irrespective of the sagittal height of the optic zone. There are four fenestrations in the optic zone and six in the scleral zone and their purpose is to prevent binding of the lens (Figure 1). Each fenestration has a diameter of 0.20 ram. The centre thickness of the semi-scleral lens is always less than 0.45 mm and the total diameter is 17.20 ram. This design saves more than 40% of the weight compared to the earlier scleral lenses and is

85

WILLEM VREUGDENHIL, ANNETTE J.M. GEERARDS AND CHARLES J.W. VERVAET

better to handle. The trial set consists of 18 lenses with optical zone sagittal heights which range from 2.7 to 4.1 mm in 0.10 mm intervals). The required sagittal height is determined by trying different lenses in order to achieve minimal corneal clearance together with limbal clearance (Figure 2).

Tear exchange is checked with fluorescein applied in the fornix and evaluated after blinking (Figure 3). After 1 h fitting is checked by pressing with a cotton tip on the scleral zone to induce spontaneous movement of the lens.

The semi-scleral contact lens is prescribed on daily wear basis with a wearing time restricted to 2 h on the first day of lens wear. On each subsequent day, 1 h of additional wear is advised. After I month, 2 months and every 6 months, a check-up examination was done which included measurement of visual acuity with the lens, keratometry and evaluation of the fit, with and without fluorescein, using the slit-lamp microscope.

Every day the patients have to remove the semi- scleral lens after 4 h of wear due to the accumulation of mucous. Afterwards the lens is cleaned and re-inserted with wetting solution. The lens is cleaned every day with a cleaning solution for RGP lenses and with 60% alcohol which is used to open the fenestrations. The lens is stored in a solution for disinfection of RGP lenses.

Results One keratoconic patient dropped out from fitting a semi- scleral lens as he was not motivated to try the lens because of its size. Successful initial RGP semi-scleral contact lens fitting was achieved in 28 eyes (17 keratoconus eyes and 11 keratoplasty eyes) All patients had an uncorrected visual acuity (VA) of less than 0.1 (6/ 60).

The mean corrected VA with the previous corrections was 0.59 (6/10)(SD 0.28) and the mean corrected VA

¢

d

F i g u r e 2 . Diagrammatic representation of the mode of fit of the semi-scleral lens. The scleral zone, a, aligns over a width of at least 2.0 mm with the sclera. In the optic zone, b depicts limbal clearance, and c represents ~orseshoe' like clearance. Apical touch is allowed at d.

R1 R2 R3 R4

F i g u r e 1. Plan and cross-section views of the semi-scleral lens. Small black circles depict the location of the fenestrations. The fourth back surface curve, R4 aligns with the selera.

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A NEW RIGID GAS-PERMEABLE SEMI-SCLERAL CONTACT LENS FOR TREATMENT OF CORNEAL SURFACE DISORDERS

with central epithelial corneal erosions and decreased visual acuity. A gas-permeable semi-scleral lens with the following specification was fitted for both eyes:

Figure 3. Fluorescein pattern of the semi-scleral lens.

~- 0.9 o

L

"6

.~ 0.7

<

. J

o . • • •

0,5 I I I I --~

0,5 0,6 0.7 0.8 0,9 1 VA with corneal lens

Figure 4. Graphical comparison of visual acuity measured with the semi-scleral lens and with a corneal lens. The correlation coefficient was 0.5 (27 data points are shown since one of these represents two eyes and results for an intolerant patient were excluded).

with the semi-scleral lenses was 0.75 (6/8) (SD 0.19) but this improvement was not statistically significant. Never- theless, all patients had higher visual acuifies with the semi-scleral lenses than with their previous lenses (Figure 3). Better tolerance was found in patients wearing semi-scleral lenses with a wearing time of 10-15 h per day compared with 4 - 6 h per day with their former lenses.

Case summaries

Case 1 A 28-year old man with bilateral keratoconus. Corneal radii measured by keratometry: RE 7.50 mm× 6.52 mm (irregular) and LE 7.15 mm x 5.94 mm (irregular). Un- corrected visual acuity was 0.1 (6/60). Repeated efforts to fit the eyes with RGP corneal lenses and also a 'Piggy Back' system failed because of discomfort associated

The sagittal height of the first three curves (optic zone) was 3.30 mm. The back vertex power of the right lens was - 11.25D and that of the left lens was - 10.50D. The patient has achieved a comfortable, 12 h, daily wearing time and visual acuities of right 0.8 (6/7.5) and left 0.7 (6/9). There have been no subjective symptoms of erosion or biomicroscopic evidence of epithelial oedema.

Case 2 A 62-year old man has a severe keratoconus affecting his right eye. In 1990, he underwent a penetrating keratoplasty in the right eye. For 6 years he has been wearing spectacles RE+1.75 s p h e r e / - 7.50 cylinder axis 120 VA 0.5. The corneal radii measured by keratometry were: RE 8.62 mm× 6.50 mm (irregular).

We fitted a gas-permeable semi-scleral lens with the following specification for the right eye:

Back vertex power 9 25D

The sagittal height of the first three curves (optic zone) was 3.80 mm. Wearing time with the semi-scleral lens has been 15 h a day on dally wear basis with a visual acuity of 0.8 (6/7.5). At the 6 months of follow-up the corneal graft has been stable. No vascularisation was found and no hypoxic signs of the graft were seen.

D i s c u s s i o n Contact lenses play a significant role in the rehabilita- tion of visual acuity in patients with corneal surface disorders. However, optimal visual acuity in irregular astigmatism cannot always be achieved because of inability to achieve a stable or comfortable fit. In this category are some patients with keratocononus, ex- treme topographic distortion caused by surgery or other trauma, and astigmatism following keratoplasty that makes corneal lens fitting desirable but problematic. It may be impossible to fit such patients with conventional contact lenses because their corneal surface cannot tolerate the friction of a rigid corneal or 'Piggy Back' lens system. We have fitted such patients with RGP semi-scleral lenses.

The use of scleral lenses dates back for more than 100 years but they have not outlived their use in many clinical situations. The main problem encountered with the scleral lens is restricted wearing time due to corneal hypoxia caused by limitations of the material used. Corneal vascularisation due to hypoxia is a well recognised complication of all forms of contact lens wear, including semi-scleral lens wear, but the cause of the hypoxia varies with different types of contact lenses. With corneal contact lenses, oxygen reaches the corneal epithelium either by diffusion through the lens or by the tear pump. Therefore, it is reasonable to consider rigid

87

WILLEM VREUGDENHIL, ANNEWI'E J.M. GEERARDS AND CHARLES J.W. VERVAET

semi-scleral lens wear for patients who develop corneal vascularisation associated with other types of contact lens wear.

Pre-existing corneal vascularisation may increase local oxygen supply and is not a contraindication to high gas-permeable semi-scleral contact lens wear, but in such cases close monitoring is essential.

published in the future. The availability of these rigid gas-permeable semi-

scleral contact lenses, with its simplified fitting techni- que and good reproducibility certainly has scope to increase the use of this lens and also rates as the first significant development in semi-scleral contact lenses for many years.

Conclusion We have outlined a method for the use of gas-permeable semi-scleral contact lenses for patients with corneal irregularities who were unable conventional contact lenses. Although still in development and clinical appraisal, the gas-permeable semi-sclerat lens appears to offer increased wearing time, higher visual acuity and a reduction in other problems commonly recognised as related to hypoxia, such as corneal vascularisation and epithelial oedema. It is also possible to incorporate almost any power into the semi-scleral lens which enables us to fit patients with very high refractive errors. Another advantage is that topical medications can be safely used in patients wearing these lenses, ff corneal vascularisation is aggravated, the wearing time must be decreased.

Our lens fitting strategy is to fit RGP lenses or soft lenses for treatment of corneal surface disorders. When inadequate tolerance is obtained, we fit the rigid semi- scleral contact lens. Without an experienced fitter and a well motivated patient, rigid gas-permeable semi-scleral contact lens is unsuccessful. Handling the semi-scleral lens, even in patients with low visual acuity, is generally no problem.

Once in 2 or 3 years the semi-scleral must be changed. The first check-up is i month after fitting, the second after 3 months and then every 6 months. Prior to fitting and annually we take endothelial photographs in order to monitor any changes. These results will be

Address for Correspondence Willem Vreugdenhil, Optometrist, Oculenti Contact Lens Practice, The Rotterdam Eye Hospital, William Boothlaan 16, 3012 VJ Rotterdam, The Netherlands.

REFERENCES

1 Geyer, O.C., Wagenbach, G. and Bohme, A. Scleral lenses today- applications and manufacturing methods. Contactologia, 17, 168- 176 (1995).

2 Vreugdenhil, W., Rijneveld, W.J., Koster, R. and Beekhuis, W.H. Cornea-pathologie en bandage lenzen. Visus, No. 2, 4-8 (1993).

3 Vreugdenhil, W., Pdjneveld, W.J. and Eggink, F.A.GJ. Fitting therapeutic SoftPerm contact lenses in the event of corneal pathology with highly irregular astigmatism. J. Br. Contact Lens Assoc., 17, 59-61 (1994).

4 Fick, A.E. A contact lens. Arch Ophthalmol., 19, 215-26 (1888). Feinbloom, W.A. A plastic contact lens. Am. J. Ophthalmol., 14, 41-49 (1937).

6 Ezekiel, D.F. Gas-permeable haptic lenses. ]. Br. Contact Lens Assoc., 6, 158-161 (1983).

7 Schein, O.D., Rosenthal, P.R., Ducharme, C. A gas-permeable scleral contact lens for visual rehabilitation. Am. ]. Ophthalmol., 109, 318-22 (1990).

s Kok, J.H.C. and Visser, R. Treatment of ocular surface disorders and dry eyes with high gas-permeable scleral lenses. Cornea, 11, 518-522 (1992).

9 Tan, T.H., Pullum, K.W. and Buckley, R.J. Medical applications of scleral contact lenses: 1. A retrospective analysis of 343 cases. Cornea, 14, 121-129 (1995).

lo Tan, D.T.H., Pullum, K.W. and Buckley, R.J. Medical applications of scleral contact lenses: 2. Gas permeable scleral contact lenses. Cornea, 14, 130-137 (1995).

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