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ORIGINAL ARTICLE
Year : 2023 | Volume
: 37
| Issue : 1 | Page : 43-47
Short-term visual outcome with sclerocorneal contact lens on irregular cornea
K Husna Noufal, Shruthi P Babu
Department of Cornea, Comtrust Eye Hospital, Kozhikode, Kerala, India
Correspondence Address:
K Husna Noufal
Comtrust Eye Hospital, Puthiyara, Kozhikode, Kerala
India
Source of Support: None, Conflict of Interest: None
DOI: 10.4103/sjopt.sjopt_268_21
PURPOSE: The purpose is to study the change in visual acuity obtained with sclerocorneal contact lens (SCL) in patients with irregular corneal astigmatism.
METHODS: A prospective pre–post observational study was designed to include consecutive consenting patients with irregular corneal astigmatism and best-corrected visual acuity worse than 6/12 and fitted with SCL. Visual acuity was assessed using Snellen charts before fitting SCL and 1 week after the fit and converted to the equivalent logMAR units for analysis.
RESULTS: We included 51 eyes of 41 patients with a mean age of 26.31 ± 8.86 of which 32 (78%) were men. Keratoconus was the most common indication (n = 42 eyes, 82.35%), followed by corneal scar (n = 3, 4%), post keratoplasty (n = 2, 4%), high myopia (n = 2, 4%), pellucid marginal degeneration (n = 1, 2%), and aphakia (n = 1, 2%). The mean overall uncorrected visual acuity improved significantly (P < 0.001) with SCL from 1.18 ± 0.34 logMAR (6/120 Snellen's equivalent) to 0.27 ± 0.15 (6/9 Snellen's equivalent) at 1-week post-SCL fitting. The mean overall best spectacle-corrected visual acuity improved from 0.89 ± 0.45 logMAR (6/36 Snellen's equivalent) to 0.26 ± 0.15 (6/9 Snellen's equivalent) at 1-week post-SCL fitting.
CONCLUSION: Sclerocorneal contact lens improves visual acuity significantly in patients with irregular corneal astigmatism and reduces the need for corneal transplantation.
Keywords: Irregular corneal astigmatism, keratoconus, sclerocorneal contact lens, visual outcome
Irregular astigmatism that occurs in a variety of corneal diseases causes pronounced visual deterioration.[1] Scleral lenses are used to improve vision in patients with high or irregular astigmatism such as keratoconus, keratoglobus, pellucid marginal degeneration, and postkeratoplasty astigmatism.[1]
Contemporary advances in contact lens designs and materials provide more fitting options for patients with corneal ectasia and irregular astigmatism.[2] A fitting sclerocorneal contact lens (SCL) is a reasonable alternative option for treating irregular corneas. They are supported by the sclera and therefore can be fitted on eyes with markedly irregular corneas. They provide significant improvement in visual acuity, high subjective comfort ratings, and prolonged usage times.[3] This is particularly important for patients with corneal irregularity when vision cannot be improved with rigid gas permeable lenses either because of the patient's poor tolerance level or inability to fit such a lens. The fluid reservoir between the lens and the ocular surface provides the moistening of the ocular surface.[4] It provides an effective option for the correction of residual ametropia and high-order aberrations and masking surface corneal irregularities with the tear lens between the posterior lens surface and the anterior corneal surface.[5] There are only few studies which have studied the visual outcome with scleral lenses in irregular corneas. In this prospective pre-post, observational study design, we evaluated the visual outcome of the patients fitted with SCLs.
MethodsThe study protocol that adhered to the tenets of the Declaration of Helsinki was approved by the Institutional Ethics Committee. Informed consent was taken from all patients before enrollment. The patients were enrolled in outpatient clinics of a tertiary eye care hospital in South India, between 2017 and 2019. Patients with irregular astigmatism due to keratoconus, keratoglobus, pellucid marginal degeneration, irregular cornea following keratoplasty, corneal opacity, high myopia, and aphakia who were unable to achieve visual acuity of 6/12 Snellen's or better with spectacles or standard designs of soft or corneal RGP contact lenses were included. Patients with severe eye dryness (Schirmer's 1 <5 mm at 1 min), endothelial decompensation with corneal stromal and epithelial edema, and active coexistent ocular disorders that might affect visual acuity were excluded from the study. Age, gender, laterality of disease, and etiology were documented.
The patients seen by two ophthalmologists were recruited for the study. The ophthalmologist seeing the patient performed a comprehensive ocular assessment including measurement of uncorrected and best spectacle-corrected visual acuity (BSCVA) using Snellen chart assessment converted to logMAR charts, dilated anterior and posterior segment examination, applanation tonometry and corneal topography (Visante AS-OCT, Zeiss, Atlas, Germany) was performed on all study patients before fitting the SCL.
Fitting of lens and follow-up schedule
All patients were fitted with a semiscleral type of sclerocorneal lens made of Flouro Silicone Acrylate (Hesafocon B, Boston XO2, Mc Asfeersclerocorneal lens), with oxygen permeability of 141, and diameter of 14.5. The trial set consisted of 14 lenses with a base curve ranging from 6.6 to 8.2 mm. A preservative-free sterile saline solution was instilled with sodium fluorescein into the concave side of the lens and it was gently inserted on to the ocular surface to avoid pressure due to suction or unwanted impingement on the conjunctiva. The central tear reservoir was checked immediately after fitting and a progressively flatter or steeper base curve was selected accordingly till an ideal vault with a tear reservoir of at least 300 μ thickness at the highest point on the cornea was obtained. The lens landing was also checked and the edge lift was evaluated. An ideal edge lift of 0.8–1 mm width, without excessive movement, impingement, or blanching of conjunctival vessels was attempted. If there was excessive movement on the peripheral landing zone, the landing zone was lowered and vice versa. If both central and peripheral fittings were acceptable, the lens was allowed to settle for a further 20 min and the fit was re-evaluated. Finally, we aimed for a lens that sat evenly approximately 1.5 mm outside the limbus [Figure 1]a and [Figure 1]b. If a decentered apex that could cause the lens to dislocate inferiorly was found, an increased diameter or steep base curve that could improve centration was used.
Figure 1: (a) SCL without fluorescein stain. (b) SCL with fluorescein stain. SCL: Sclerocorneal contact lensThe lens movement was judged at 6 o'clock by asking the patient to look up and blink. A lens movement of about 0.5 mm was considered adequate. Decreasing the edge lift, steepening the base curve, increasing the diameter, or a combination of these that could help to decrease the excessive lens movement were adopted. Opposite parameter changes were applied to increase the movement. Once the lens with appropriate parameters was obtained, an accurate over-refraction was performed. The fitting was evaluated twice, first after 20 min of lens insertion and second after 4–6 h. The over-the-lens acceptance of power was checked with fogging method for distance and also for unilateral near vision. Unwanted near addition could be due to over or incorrect acceptance for distance. In such cases, refraction was repeated with fogging. The final lens was ordered from the manufacturer by adding the power to the trial lens power.
At the time of dispensing the lens to patients, all Instructions regarding the proper way of lens insertion, removal, and cleaning, were given. In addition, users were educated on the use of the lens and made to practice insertion and removal multiple times under supervision.
Uncorrected and best-corrected visual acuities were assessed at the time of dispensing and after 1 week.
Statistical analysis
Data analysis was done using the Spyder is a free and open-source scientific environment written in Python, for Python which is also free and open-source software that is GNU General Public License(GPL)-compatible. The paired-t-test was used to assess the difference between pre and post-fitting data and a P < 0.05 was considered statistically significant. Visual acuity measurements were converted to logMAR for analysis.
ResultsWe included 51 eyes of 41 patients with irregular corneal astigmatism, with a mean age of 26.31 ± 8.86, and majority of cases belonged to 20–30 years of age group.
[Table 1]. Thirty-one patients were fitted with the lens in one eye and ten patients in both eyes. Of the 41 patients evaluated, 32 (78%) were men and 9 (22%) were women. The most common indication for SCL was keratoconus-42 eyes (82.35%). This was followed by the corneal scar in three eyes (5.88%), postpenetrating keratoplasty in two eyes (3.92%), high myopia in two eyes (3.92%), pellucid marginal degeneration in one eye (1.96%), and aphakia in one eye (1.96%).
There were 34 patients with keratoconus of which 27 were male. The mean keratometry value in the keratoconus population was 55.07 ± 8.6 [Table 2].
Visual outcome
The mean overall uncorrected logMAR visual acuity improved significantly from 1.18 ± 0.34 (6/120 Snellen's equivalent) to 0.27 ± 0.15 (6/9 Snellen's equivalent) with sclero-corneal contact lens fitting (P < 0.001). The mean overall best spectacle-corrected log MAR visual acuity improved (P < 0.001) from 0.89 ± 0.45 to 0.26 ± 0.15, with P = 3 * 10^-14, P < 0.05 [Table 3].
Table 3: Improvement in uncorrected and best-corrected visual acuity after fitting with sclerocorneal contact lensKeratoconus was the major indication for fitting of corneoscleral contact lens. The mean overall best spectacle-corrected logMAR visual acuity improved significantly (P < 0.001) from 0.90 ± 0.46 to 0.26 ± 0.15. [Table 4] presents a comparison of the change in visual acuity with respect to underlying etiology.
Table 4: Change in visual acuity with sclerocorneal contact lens in different aetiologies of irregular corneal astigmatism[Figure 2] represents the box plot comparison of the best spectacle-corrected logMAR visual acuity and that obtained with SCL. Vision improved significantly with SCL.
Figure 2: Box plot comparison of the mean of the best spectacle-corrected distance log MAR visual acuity (BSCVA) with the visual acuity obtained with SCL. SCL: Sclerocorneal contact lens, BSCVA: Best spectacle-corrected visual acuity Discussion The results of the study demonstrate the therapeutic efficacy of SCLs for visual rehabilitation of irregular corneas for which other treatment methods are less effective or not suitable. Keratoconus was the primary indication for sclero-corneal lens wear and experienced significant improvement in visual acuity. As the number of patients in other groups was very low, the statistical significance in the improvement of vision could not be assessed.
Fitting of scleral contact lens in keratoconus is indicated when all other lenses fail to improve the vision or because of the inability to get an optimal fit with RGP, RGP intolerance, advanced keratoconus, and stromal scarring. There is a renewed interest over the last few years because of the availability of high Dk material and newer designs. The fitting of contact lens can improve the vision and delay or obviate the need for keratoplasty in keratoconus. Corneal vaulting, centration, and excellent comfort have allowed expanding the use of corneoscleral lenses in less severe keratoconus cases too.[6] The disadvantages of the scleral lens are the care regimen, difficult insertion and removal technique using plungers, and the frequent change of saline bottles.[7] Optical coherence tomography imaging has allowed modern scleral lens fitting by providing accurate measurements for trial lens selection and contact lens fit assessment and preventing ocular complications associated with lens application.[8]
Collagen cross linking stabilizes the disease progression in keratoconus. Intracorneal ring segments flatten the cornea and are used to reduce refractive errors and PK, DALK, and Bowman's Layer transplantation are performed in the advanced stages of the disease.[9] Contact lenses have an important role as an effective option for visual rehabilitation in keratoconus. Choosing the appropriate type of lens and proper fitting can help avoid the need for corneal transplantation in severe cases of keratoconus. Even after corneal grafting, patients may need special contact lenses to correct residual astigmatism.[10] The use of specialty lenses specifically the sclerocorneal lens has led to a decreased need for corneal transplants in severe keratoconus as defined by K max ≥70 D.[11] Other indications of scleral lenses include mucous membrane pemphigoid,[12] persistent epithelial defect, and dry eye disease secondary to GVHD or chemical burns.[13]
We have got a very significant improvement in both uncorrected and best spectacle-corrected visual acuity after SCL fitting [Table 3]. Keratoconus patients are commonly adolescents or young adults and may require corneal surgery during their lifetime. Keratoplasty procedures are associated with risks such as infection, rejection, and severe astigmatism. Improvement in visual acuity with SCL can bring down the rate of keratoplasty in patients of keratoconus and thereby significantly reduces the cost, effort, and other issues related to the maintenance of corneal grafts.[1]
Five patients discontinued the SCL within 3 months. One high myopic patient who was dispensed with the SCL in both eyes discontinued the lens because of the cosmetic blemish. Other patients discontinued it because of the difficulties in insertion and removal.
In a study by Abou Samra et al.,[3] marked improvement in visual acuity was demonstrated in all studied patients with irregular corneas who were fitted with a new design of corneoscleral contact lens namely Rose K2 XL. They reported statistically significant improvement in nearly all measured subjective parameters with a high degree of patient comfort and satisfaction using a self-administered questionnaire. In another study of clinical application and therapeutic outcomes of scleral contact lenses by Preeti et al.,[14] scleral contact lenses were shown to be effective in the management of various degrees of irregular corneas of different aetiologies, with the major indication being keratoconus as in our study. Significant improvement in quality of life was also demonstrated in the study. In another study by Fuller and Wang,[15] excellent safety and efficacy of scleral contact lenses in keratoconus were demonstrated.
Ours is a single-center study in a tertiary eye care center in South India. The detailed ocular assessments and documentation were done by two ophthalmologists at the same center. We have a high number of patients compared to other studies and it is the strength of our study. The limitation of our study is that we did not assess the subjective comfort of the patients and the study was limited to the 1st week after the lens fitting. We chose the initial week after lens fitting because we can assess the difficulties in insertion and removal, comfortable wearing time, and address other related issues in the immediate days after lens dispensing. During lens dispensing, we give a good educational session for the patients regarding insertion, removal, and proper hygienic care of the contact lenses and make them practice themselves with insertion and removal. This helped to reduce the worries of patients well and helped to reduce the dropouts. We do not have long-term follow-up due to the pandemic as the follow-up visits were restricted to the hospital and we had to reach out to the patients through teleconsultation.
ConclusionIn summary, SCL provide an excellent visual outcome in patients with the irregular cornea and obviates the need for corneal transplantation. Further studies are needed to look into the long-term outcome and complications of the SCL in the long run.
Acknowledgment
The authors would like to acknowledge Dr. Praveen Nirmalan, Mentor at AMMA Education and Research Foundation for providing guidance in manuscript preparation. Similarly, the authors would like to thank Mr. Ajmal Ashraf, Research Assistant, Comtrust Eye Hospital for his support in the work.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
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