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 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 4  |  Issue : 2  |  Page : 73-76

Scleral contact lenses for visual rehabilitation in keratoconus and irregular astigmatism after refractive surgery


1 Department of Ophthalmology, Mackay Memorial Hospital, Taipei, Taiwan
2 Department of Ophthalmology, Mackay Memorial Hospital; Mackay Medicine, Nursing and Management College, Taipei, Taiwan

Date of Web Publication6-Jun-2014

Correspondence Address:
Huey-Chuan Cheng
Department of Ophthalmology, Mackay Memorial Hospital, Number 92, Section 2, Zhongshan North Road, Zhongshan District, Taipei City 104
Taiwan
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Source of Support: None, Conflict of Interest: None


DOI: 10.1016/j.tjo.2014.02.002

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  Abstract 


This study aims to report our experience of using fluid-ventilated, gas-permeable scleral contact lenses (SCLs) for visual rehabilitation of patients with keratoconus and irregular astigmatism after refractive surgery. This is a noncomparative interventional case series reporting eight consecutive patients fitted with SCLs because of irregular astigmatism following the failure of other optical corrections. Retrospective chart review and data analysis included age, sex, etiology prior to lens fitting, visual outcomes, follow-up time, and complications. Twelve eyes of eight patients were studied. All eyes were fitted with SCLs due to unsatisfactory vision with spectacle correction or other contact lens modalities. Five eyes had keratoconus and seven had irregular corneas post refractive surgery. The mean follow-up period was 14.4 ± 1.3 months (range 11–17 months). The mean age was 32.63 ± 7.68 years (range 18–48 years). The average steepest keratometry(Kmax) of our series was 49.56 ± 12.2 D. The mean refractive astigmatism was 5.50 ± 5.3 D. The mean best corrected visual acuity (BCVA) in logarithm of the minimum angle of resolution improved from 0.71 ± 0.50 (range 0.10–1.40) to 0.05 ± 0.07 (range 0.00–0.15) after SCL fitting (p < 0.001). All reported eyes achieved significant improvement in the BCVA with SCL fitting. None of the patients discontinued to wear SCLs. SCLs should be considered lenses of choice in irregular corneas refractory to conventional optical correction.

Keywords: ectasia, irregular astigmatism, keratoconus, refractive surgery, scleral contact lens


How to cite this article:
Lo HL, Yeh SI, Cheng HC. Scleral contact lenses for visual rehabilitation in keratoconus and irregular astigmatism after refractive surgery. Taiwan J Ophthalmol 2014;4:73-6

How to cite this URL:
Lo HL, Yeh SI, Cheng HC. Scleral contact lenses for visual rehabilitation in keratoconus and irregular astigmatism after refractive surgery. Taiwan J Ophthalmol [serial online] 2014 [cited 2020 Sep 21];4:73-6. Available from: http://www.e-tjo.org/text.asp?2014/4/2/73/204029




  1. Introduction Top


Scleral contact lenses (SCLs) have lately become an important tool for visual rehabilitation of patients with irregular corneas or severe ocular surface disorders. The first description of SCLs in the medical literature was provided in a report on contact lenses by Adolf Eugen Fick in 1888. The early SCLs were made of glass, which were impermeable to oxygen and difficult to manufacture. The introduction of polymethyl methacrylate as a lens material made the manufacture of lenses easier, but significant hypoxia of the cornea caused by the lens material remained a critical drawback; meanwhile, inadequate limbal clearance and problems with back surface junctions were also noticed.[1],[2],[3] The introduction of rigid gas-permeable (RGP) materials with sufficiently high gas permeability (Dk) reduced corneal hypoxia significantly. Technological innovations in the design and manufacturing of SCLs, such as fenestration design that allows air ventilation or haptic design with channels or contours that allows fluid ventilation with no intrusion of air bubbles, solved problems related to lens suction and opened new perspectives for SCL use.[4],[5]

Conventional RGP contact lenses can mask complex optical aberrations by allowing a tear lens to form between the contact lens and the irregular corneal surface. However, they may not be suitable in patients who cannot adapt to lens sensation or in those with significant irregularities of the anterior corneal surface that preclude an adequate lens centration and stability, leading to frequent contact lens dislocations.[6] SCLs are advantageous as they are supported by the sclera without any touch of the cornea, thus remaining stable in a centered position and providing nonsurgical options for visual correction. The constant precorneal liquid reservoir between the lens and the cornea both neutralizes irregular astigmatism and confers a continuous moist environment that protects the cornea from exposure to air and friction of blinking.[7] SCLs have gained popularity among contact lens practitioners worldwide and are used in a spectrum of corneal disorders to promote optical correction of an irregular corneal surface. Successful visual rehabilitation with SCL fitting was reported in primary corneal ectasias such as keratoconus, keratoglobus, and pellucid marginal degeneration; and in secondary irregular corneas post refractive surgery, penetrating keratoplasty, or trauma.[8],[9],[10],[11],[12],[13] The use of SCLs has become an important therapeutic strategy in the treatment of irregular corneas refractory to conventional nonsurgical therapy.

In recent years, SCLs are increasingly gaining importance as a treatment option for ocular surface diseases. The large size and scleral bearing surface of SCLs can help retain a precorneal tear reservoir for corneal hydration, providing total protection from the external environment, lid margins, and lashes. SCLs may relieve pain, prevent exposure keratitis, and enhance epithelial healing in severe ocular surface diseases such as severe keratoconjunctivitis sicca,[14] chronic graft-versus-host disease,[14],[15] Stevens–Johnson syndrome,[16] toxic epidermal necrolysis,[16] ocular cicatricial pemphigoid,[17] limbal stem cell deficiency,[18] persistent corneal erosion,[19] exposure keratopathy,[20] neurotrophic keratopathy,[21] and atopic keratoconjunctivitis.[22] Moreover, SCLs may serve as a useful adjunct in drug delivery for corneal neovascularization, and maintenance of a healthy ocular surface and visual function during delayed repair of surface defects.[23],[24]

In this case series, we report our experience with fluid-ventilated, gas-permeable, corneoscleral lenses (HiClear; Taiwan Macro Vision Corp., Taipei, Taiwan) fitted in 12 consecutive eyes for visual rehabilitation due to keratoconus and irregular astigmatism post refractive surgery, which were refractory to conventional nonsurgical therapy, and a review of literature.


  2. Methods Top


We retrospectively reviewed the medical records of eight consecutive patients fitted with SCLs for visual rehabilitation of irregular astigmatism at Mackay Memorial Hospital, Taipei, Taiwan, from September 2012 to March 2013. The study was approved by the Research and Ethical Committee of the Mackay Memorial Hospital. All patients have been referred due to visual dissatisfaction after failure of nonsurgical methods of visual rehabilitation such as glasses or contact lenses. Patients who were unable to handle the SCLs or showed poor compliance for follow-up were excluded from the analysis. Data on age, sex, diagnoses, ocular history, previous contact lens experience, and indication for SCL fitting were collected. The best corrected visual acuity (BCVA) with any conventional optical correction and best corrected visual acuity with SCL fitting (BCVA-SCL) were recorded. Visual acuity was measured using the Landolt C chart and converted to the logarithm of the minimum angle of resolution (logMAR). Slit-lamp bio-microscopy findings such as conjunctival abnormalities, corneal opacities, and corneal vascularization and their location were recorded. Topographic images and simulated keratometry (OPD-Scan II; Nidek, Gamagori, Nagoya, Japan) were obtained prior to fitting SCLs for all patients unless the corneal surface was too irregular to provide meaningful videokeratoscopic data. SCL fitting was considered successful if a functional improvement was observed in patients’ quality of vision.

Our patients were fitted with HiClear corneal scleral lenses (Taiwan Macro Vision Corp.), which were made up of a highly gas-permeable material of fluorosilicone acrylate copolymer, Fluo-roPerm 60 (paflufocon B; Paragon Vision Sciences, Mesa, Arizona, USA). Its oxygen transmissibility (Dk) is 60 × 10 −11 Fatt units at 35°C (International Organization for Standardization/Fatt method). It is inherently wettable, making plasma treatment optional. All scleral lenses were lathe cut at an authorized laboratory (Taiwan Macro Vision Corp.). The overall lens diameter was in the range 7–16 mm and the optic zone was 7.30 mm. The average central thickness of the lenses was 0.22 mm and the power ranged from −20.00 D to +20.00 D in 0.25 D steps. Base curves ranged from 6.50 mm to 9.00 mm.

All patients in our series were fitted with 14.0–15.0-mm-diameter diagnostic lenses, including standard and keratoconus designs. These corneo-SCLs were designed to distribute pressure, equally, along the corneal and scleral surfaces. The selection of the initial diagnostic SCL differs from that of corneal lens, for appropriate sagittal deptph (SAG) is more important than alignment with the central cornea in SCL fitting.[8] SAG is determined by the rate of curvature as well as the area of the curve. We based our initial diagnostic lens selection on the reference sphere from the elevation map generated by a corneal topographer and external observation of the profile of the anterior corneal surface. Fitting goals included complete limbal clearance and scleral alignment, with little or no blanching of the conjunctival vasculature. A larger SAG lens would be tried if associated findings suggest the trial lens to be too shallow or lens SAG inadequate as sectorial edge lifts. A lens with smaller SAG would be tried if associated findings suggest the trial lens to be too deep or associated with excessive SAG, for example, tight peripheral fit (blanching of conjunctival vasculature) or excessive clearance (air bubble under optic zone). Once proper SAG was achieved, the base curve would be adjusted to achieve adequate mid-peripheral clearance. A change in the base curve alone will not change the SAG of the lens [Figure 1]. The peripheral curve was then adjusted to optimize the fit. The last step is spherocylindrical over-refraction. The optimal lens vault and perimeters of individual lenses were determined by on-eye evaluation. A single examiner (H.C.C.) fitted the lenses for all patients.
Figure 1: Changing the base curve while keeping the sagittal depth unchanged. The peripheral curve system compensates for the base curve changes to maintain sagittal depth. The base curve was flattened to increase the mid-peripheral vault and steepened to decrease it.

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Statistical analysis compared the outcomes according to the two reported diagnoses, keratoconus and irregular astigmatism post refractive surgery. The groups were compared using Mann–Whitney U test, and p < 0.01 were considered statistically significant.


  3. Results Top


In this case series, 12 eyes of eight patients were included. The main indication for scleral lens fitting was failure of other modalities (intolerance, instability, or unsatisfactory vision improvement). Regarding the etiology prior to lens fitting, five eyes had keratoconus and seven irregular corneas post refractive surgery. Five of these underwent post radial keratectomy and two post laser-assisted in situ keratomileusis. The mean follow-up was 14.4 ± 1.3 months (range 11–17 months). The mean age was 32.63 ± 7.68 years (range 18–48 years). The average steepest keratometry (Kmax) of our series was 49.56 ± 12.2 D and the mean refractive astigmatism 5.50 ± 5.3 D. Significant differences were observed among the outcomes when comparing keratoconus and irregular astigmatism post refractive surgery eyes. The mean age of patients with keratoconus and irregular astigmatism post refractive surgery was, respectively, 22.0 ± 5.3 years (range 18–28 years) and 39.0 ± 7.7 years (range 31–48 years). Patients with keratoconus who needed SCL corrections for visual rehabilitation were younger than those with irregular corneas post refractive surgery (p < 0.01). Moreover, higher corneal irregularity was observed in keratoconus eyes when compared with irregular corneas after refractive surgery. The average Kmax was 62.3 ± 6.9 D in keratoconus and 40.5 ± 3.0 D in post refractive surgery eyes (p < 0.01). Refractive astigmatism was 10.25 ± 5.6 D and 2.11 ± 1.79 D in keratoconus and post refractive surgery eyes, respectively (p < 0.01). The mean BCVA in logMAR improved from 0.71 ± 0.50 (range 0.10–1.40) to 0.05 ± 0.07 (range 0.00–0.15) after SCL fitting. This improvement was highly statistically significant (p < 0.001). All reported eyes achieved significant improvement in the BCVA with SCL fitting. Neither any patients discontinued to wear SCLs, nor any complications related to SCL fitting were observed during the follow-up period of at least 6 months. Diagnoses and data of the patients fitted with SCLs are summarized in [Table 1].
Table 1: Clinical features and data summary of patients fitted with scleral lenses.

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  4. Discussion Top


Several designs of SCLs have been described in published literature. Their classification is mainly based on the bearing and clearance relative to the average corneal diameter (12.8 mm) rather than the diameter of the lens. Corneo-SCLs (12.9–13.5 mm) have corneal bearing and scleral touch. Semi-SCLs (13.6–14.9 mm) have both corneal and scleral bearing. Mini-SCLs (15.0–18.0 mm) have scleral bearing and minimal corneal clearance, although the narrow haptics on mini-SCL provides a smaller area of landing over the sclera, a fact that frequently leads to excessive compression near the limbus. Full SCLs (18.1–24.0 mm) have complete corneal clearance and broader area of sclera alignment, resulting in reduced limbal compression.[4],[9],[25],[26] Full SCLs are individually built, with three distinct areas: corneal, limbal, and haptic. Every zone is made up of a series of smooth, constantly flattening multicurves, according to the ocular surface, thus enabling easy tear exchange under the lens. The bearing portion, the haptic, is supported completely by the sclera and does not contact the cornea. The central optic portion with its artificial tear-filled reservoir corrects front surface refractive error, including irregular astigmatism, and power can be added to correct axial refractive error. Fitting goals included complete corneal clearance, complete limbal clearance, and scleral alignment with little or no blanching of conjunctival vasculature.[8]

Despite increasing awareness of the potential benefits of the SCLs, their widespread use may be limited because of the perception that fitting is time consuming and troublesome. To date, no specific guidelines for fitting SCLs have been established or published. Schornack and Patel[27] reported that the base curve of SCLs correlates with the reference sphere and steep and flat keratometric powers from topographic analysis; however, the predictive relationship is weak. Our study findings were similar, as we could not find a close association between any single topographic index and the base curve of the final SCLs prescribed. Diagnostic fitting may be the most efficient method of fitting SCLs at present, which allows the patient to experience the sensation and vision that can be expected prior to the complete fitting process. With the use of standard diagnostic trial sets, the procedure of fitting SCLs may be similar to that of fitting corneal or corneo-SCLs.

Variable contact lens options are available, such as RGP lenses, hybrid lenses, custom hydrogels, and piggyback systems, which provide adequate management of most cases of irregular cornea astigmatism.[9] SCLs have been reported to improve visual acuity when these treatment modalities have failed. In our study, vision improvement was the primary indication, and the results support the ability of SCLs to promote visual improvement in these challenging cases. In our series, we could achieve a BCVA of better than 20/40 in all patients, and the mean BCVA-SCLs in logMAR improved from 0.71 ± 0.50 to 0.05 ± 0.07 after SCL fitting (p < 0.001). Compared with the study by Visser et al,[26] the level of improvement in the BCVA (with and without SCLs) differed significantly among the diagnosis groups, with the highest median increases being seen in eyes with keratoconus (0.50) and lowest in those with keratitis sicca (0.20). In our series, relatively good results may be attributed to the selection bias of our patients, because only patients satisfied with BCVA achieved by SCL fitting were included in the study.

Currently, the ideal lens fitting evaluation is performed clinically through slit-lamp observation. However, even very experienced practitioners can have difficulty in determining limbal clearance by slit lamp, and a very thin fluorescein layer may easily be missed by a human observer. Recently, the application of anterior-segment optical coherence tomography (AS-OCT) has been extended for custom design and evaluation of large-diameter scleral lenses. The modern AS-OCT with resolution as high as a few microns can be used to avoid refitting in cases with just enough limbal clearance. With the aid of AS-OCT, we can evaluate the interaction of the SCLs with the peripheral cornea and sclera, and possibly design varying landing profiles in different lens quadrants.[28] In recent years, the customized scleral lens prosthetic device with wavefront-guided optics was capable of correcting higher-order aberrations of irregular cornea. In a study by Sabesan et al,[29] this correction resulted in significant improvement of mean visual acuity (1.9 lines) and contrast sensitivity in patients with advanced keratoconus.

Despite all the benefits provided by SCLs, several unanswered questions regarding to its use still remain. SCLs are designed to rest on bulbar conjunctiva. The lens may depress this pliable tissue in some eyes and result in a swollen and injected paralimbal area due to compression, thus significantly decreasing the exchange of tears underneath the lens. When the exchange of liquid between the lens and the anterior ocular surface is dampened due to a lens seal-off, debris and metabolic waste accumulate over time and the cornea is exposed to a toxic swamp, which may lead to severe punctate epithelial keratopathy, corneal ischemia, and edema. Aspiration of fresh tears under the lens edge provides additional oxygen supply to the cornea and has been shown to be associated with successful fitting and increased wearing time.[13] Ortenberg et al[10] reported a 26% failure rate of SCL in a 6-year follow-up study of patients with irregular astigmatism from various reasons. They found a significant correlation between taking brief breaks during daily wearing time and the success rate, as patients who took a brief diurnal break had a 95.8% success rate for SCL wearing. Oxygen transmissibility is another issue, which is related to lens material, center lens thickness, and reservoir thickness. SCLs were designed with increasing center thickness to avoid flexure and reservoir thicknesses ranged from 100 μm to 400 μm; both inevitably decreased transmissibility of oxygen. To avoid hypoxic-related edema, Michaud et al[30] recommend to use lenses with the highest Dk (>150), with a maximum central thickness of 250 μm, and to not vault the cornea by more than 200 μm.[10] Moreover, limbal stem cells are vital to corneal epithelial health and integrity. SCLs may compromise the integrity of these stem cells, which can be attributed to corneo-SCL wearing or decentered SCLs. Long-term follow-up are required to determine whether corneo-SCL wear predisposes patients to limbal stem cell deficiency.

In conclusion, an SCL is a useful nonsurgical option that provides good visual rehabilitation in patients with keratoconus and irregular astigmatism post refractive surgery. It may postpone or even prevent the need for keratoplasty and should be considered as lenses of choice in irregular corneas refractory to conventional optical correction.

Conflicts of interest: All authors declare no conflicts of interest.



 
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