Korean J Ophthalmol > Volume 37(2); 2023 > Article
Lee, Moon, Nam, Jang, Kim, Tchah, and Lee: Scleral Lens Applications Focused on Korean Patients with Various Corneal Disorders

Abstract

Purpose

We aimed to report on the clinical outcomes of scleral lens applications in Korean patients with various corneal disorders.

Methods

This retrospective review was conducted for 62 eyes of 47 patients who had been fitted with scleral lenses for various corneal disorders. The patients were referred for inadequate spectacle-corrected visual acuity and rigid gas permeable (RGP) or soft contact lens intolerance. Uncorrected visual acuity, habitually corrected visual acuity, best lens-corrected visual acuity, topographic indices, keratometry indices, and lens parameters were evaluated.

Results

Twenty-six eyes of 19 patients with keratoconus were enrolled. Other conditions included corneal scar (13 eyes of 12 patients), phlyctenules (three eyes), laceration (four eyes), chemical burn (one eye), keratitis (one eye), Peters’ anomaly (one eye), fibrous dysplasia (one eye), ocular graft-versus-host disease (two eyes of one patient), irregular astigmatism (18 eyes of 12 patients), and corneal transplant status (five eyes of four patients). The mean topographic values of the eyes include flat keratometric value (43.0 ± 6.1 diopters [D]), steep keratometric value (48.0 ± 7.4 D), and astigmatism (4.9 ± 3.6 D). Of the eyes fitted with scleral lenses, best lens-corrected visual acuity (0.10 ± 0.22 logarithm of the minimum angle of resolution [logMAR]) was significantly better than the habitually corrected visual acuity (0.59 ± 0.62 logMAR, p < 0.001).

Conclusions

Scleral contact lenses are a good alternative for patients with corneal abnormalities and those who are intolerable to RGP contact lenses, resulting in both successful visual outcomes and patient satisfaction, especially concerning keratoconus, corneal scar, and corneal transplant status.

The rigid gas permeable (RGP) contact lens, which can mask irregular astigmatism as well as provide optical correction, appears to be a promising option for patients with irregular corneas resulting from scars and neovascularization [1,2]. However, it is difficult for patients with severe or advanced corneal lesions to center the RGP lens, and the visual acuity improvement is not significant due to poor fitting [3].
Scleral lenses have a large diameter, the smallest scleral lenses are approximately 14.5 mm in diameter, and the largest can be up to 24 mm. They are rigid, gas-permeable devices supported by the sclera and measurably vault the cornea and limbus. Thus, they can maintain a fluid reservoir in the space between the posterior surface of the lens and the anterior surface of the cornea [4]. The position of the lens is less affected by the cornea, especially in diseases such as keratoconus or scars resulting from keratitis or trauma [5]. Moreover, scleral lenses can correct refractive errors and even much higher order aberrations resulting from the irregularity of the anterior surface of the cornea [6].
In a survey conducted on practitioners in the United States, the average lens diameter prescribed by practitioners was approximately 16 mm, and the ranges of diameters used were <15 (18%), 15 to 17 (65%), and >17 mm (17%) [7]. Regular scleral lenses are large and sometimes difficult to fit in patients with ocular surface disease who may have a shortened fornix and multiple conjunctival problems [8]. Furthermore, Asian population has smaller palpebral fissures with tighter eyelids compared to the Western population, and it also may restrict patients’ tolerability of wearing a large scleral lens [9]. Thus, the approach to scleral lens prescription for Asian patients with a shallow or short conjunctival sac should be different. Proper fitting of the scleral lens avoids interaction with the irregular sclera, leading to more comfortable lens wear and better visual outcomes [10].
Despite the increasing number of prescriptions for scleral lenses, reports concerning scleral lens prescriptions that focus on corneal disorders in Asian patients are limited [8]. Therefore, in the present study, we reported the clinical features of patients fitted with scleral lenses (Onefit, Medi-Optics) with various corneal disorders referred for inadequate spectacle-corrected visual acuity and RGP or soft contact lens intolerance.

Materials and Methods

Ethical statements

The study was approved by the Institutional Review Board of Asan Medical Center, University of Ulsan (No. 2022-0097). All procedures adhered to the tenets of the Declaration of Helsinki. The requirement for informed consent was waived due to the retrospective nature of the study.

Study design

This retrospective review was conducted for 62 eyes of 47 patients who had been fitted with scleral lenses, and observations were conducted over 3 months. Patients were diagnosed with keratoconus, postpenetrating keratoplasty status, irregular astigmatism, corneal opacity due to phlyctenules, infectious keratitis, Peters anomaly, fibrous dysplasia, graft-versus-host disease, and trauma (e.g., lacerations and chemical burns). All patients were prescribed scleral lenses due to inadequate spectacle-corrected visual acuity, RGP, or soft contact lens intolerance. Patients with infectious keratitis, endothelial cell dysfunction, and glaucoma were excluded. The evaluation was also conducted after dividing into four causative disease groups: keratoconus, penetrating keratoplasty status, irregular astigmatism, and corneal opacity.

Lens fitting and data collection

The Onefit scleral lens is fabricated from a gas-permeable fluorosilicone acrylate polymer, Acuity 100 (Acuity Polymers Inc), and has an oxygen permeability (Dk) value of 100 × 10−11 cm2 · mL O2/sec · mL · mmHg. Its overall diameter ranges from 14.1 to 15.3 mm, with a standard size of 14.9 mm standard. The Onefit variant, developed for smaller corneas, has a size of 14.7 mm. It is designed to control and reproduce a peripheral recess to accommodate any offending scleral elevations using Controlled Peripheral Recess technology.
Before contact lens fitting and at each follow-up visit, all patients underwent comprehensive ophthalmic examination, including the measurement of uncorrected distance visual acuity (UCVA), habitually corrected visual acuity (HCVA) before scleral lens trial, best lens-corrected visual acuity with scleral lenses (BLCVA), and slit-lamp examination. The irregularity and astigmatism of the anterior cornea was evaluated using an autorefractive keratometer (KR-1, Topcon Corp) and slit-scanning topography (Orbscan, Bausch & Lomb). We fitted the scleral lenses by changing the sagittal height based on corneal clearance according to the manufacturer’s fitting guide. Corneal clearance was evaluated using a 40° oblique slit-lamp, and the ideal clearance after the lens had settled for 30 minutes was 200 to 225 μm at the point of highest corneal elevation. The lens power was determined by performing a refraction over the scleral lens. Scleral lenses were prescribed 2 weeks after fitting a trial lens. Subsequently, patients were followed up for at least 3 months. The success rate and adverse events were also evaluated.

Statistical analysis

All visual acuities were converted to the logarithm of the minimum angle of resolution (logMAR) for data analysis. The recorded data were analyzed using IBM SPSS ver. 24.0 (IBM Corp). Descriptive statistics were used to summarize patient characteristics and clinical outcomes. The t-test was used to determine statistically significant changes in clinical outcomes. A p-value of <0.05 were considered statistically significant.

Results

A total of 62 eyes of 47 patients (27 men, 20 women) with scleral lenses applied were included. The mean age was 33.9 ± 15.36 years (range, 6 to 72 years), and the baseline best-corrected visual acuity was 1.03 ± 0.81 logMAR (range, 0 to 2.60 logMAR). The most common indication for fitting with a scleral lens was keratoconus (26 eyes, 41.9%). Other indications included corneal scar (13 eyes, 21.0%) due to phlyctenules (three eyes), corneal laceration (four eyes), chemical burn (one eye), keratitis (one eye), Peters anomaly (one eye), fibrous dysplasia (one eye), ocular graft-versus-host disease (two eyes); irregular astigmatism (18 eyes, 29.0%), associated with post-refractive surgery (11 eyes), posterior polymorphous corneal dystrophy (two eyes) and monocular diplopia (five eyes); and corneal transplant status (five eyes, 8.1%). A total of 42 eyes (67.7%) had been using spectacles for correcting visual acuity before using the scleral lens. Five eyes (8.1%) were provided RGP contact lenses, and two (3.2%) were provided soft contact lenses. Table 1 provides additional details on the baseline demographic data of the study population.
Comparative data for corneal astigmatic indices, lens fitting parameters, UCVA, HCVA, BLCVA, differences between UCVA and HCVA, differences between BLCVA and HCVA for each group are presented in Tables 2 and 3. The initial corneal indices varies according to the corneal status. The flat keratometry values in keratoconus groups were steep compared to those of other disease groups (topographic indices, 47.3 ± 4.9 diopters [D]; keratometry indices, 46.6 ± 3.0 D). Patients with irregular astigmatism exhibited flat keratometry values compared to those of other groups (topographic indices, 39.3 ± 2.6 D; keratometry indices, 39.6 ± 2.6 D). Patients with corneal transplant status and corneal scar exhibited variable flat keratometry values (Table 2).
Sixty eyes received 14.7-mm standard design Onefit A scleral lenses, one eye with a 14.4-mm diameter scleral lens because of a narrow palpebral fissure, and another with a 14.9-mm diameter design because of a large horizontal visible iris diameter. The mean power of the lens was −3.7 ± 4.4 D, and the mean base curve was 7.80 ± 0.56 mm.
The mean UCVA was 1.03 ± 0.81 logMAR (range, 0 to 2.60 logMAR), and the mean HCVA was 0.59 ± 0.62 log-MAR (range, 0 to 2.60 logMAR). Table 3 shows that following scleral lens fitting, the BLCVA improved to 0.10 ± 0.22 logMAR (range, −0.08 to 2.60 logMAR). The differences between the UCVA and HCVA were statistically significant in all groups except for the corneal transplant status group (p = 0.067). The differences between the BLCVA and HCVA were statistically significant in all groups (p < 0.05) (Table 3). After scleral lens fitting, 58 eyes achieved best lens-corrected visual acuities >0.4 log-MAR; however, four were <0.4 logMAR (Table 4).
After a 3-month follow-up period, seven patients (14.9%; 10 eyes, 16.1%) discontinued scleral lens wear. Three patients (four eyes) who had undergone previous refractive surgery stopped wearing scleral lenses due to persistent glare and monocular diplopia with an inadequate improvement of visual acuity. Two patients (three eyes) abandoned lens wear due to the difficulty of insertion and removal of the lenses. One patient with keratoconus stopped wearing bilateral scleral lenses due to a lack of visual acuity improvement. Another patient used a scleral lens because of corneal opacity after corneal laceration but stopped wearing it due to unintentional visual acuity improvement without the scleral lens.

Discussion

The potential benefits of scleral lenses in patients with various ocular conditions have been steadily increasing with the development of anterior segment images and lens materials. However, there are a limited number of reports on scleral lens prescriptions specifically focused on treating corneal disorder in Asian patients. In this study, we evaluated the corneal astigmatism indices, visual acuity improvement, and lens parameters of scleral lens-wearing patients with various corneal disorders referred for inadequate spectacle-corrected visual acuity and RGP or soft contact lens intolerance.
Keratoconus is the most common diagnosis (19 patients, 40.4%; 26 eyes, 41.9%) since it is difficult to center the RGP contact lens on a steep cornea. Studies have assessed the efficacy of scleral lenses and improvement in quality of life in keratoconus patients [11-14]. One prospective study evaluated the effects of scleral lenses in patients with keratoconus and showed significant improvement in visual acuity and visual functioning [11]. In our study, visual acuity improved significantly compared to HCVA, and 24 fitted eyes (92.3%) a chieved a BLCVA of at least 0.4 log-MAR, as compared to 14 eyes (53.8%) before lens fitting (Table 4). Two eyes with keratoconus failed to achieve a BLCVA of at least 0.4 logMAR. One eye with severe keratoconus underwent corneal crosslinking three times. The steep keratometry indices on an Orbscan showed 61.0 D and a central corneal thickness of 332 μm (Fig. 1). Another patient also underwent corneal crosslinking and intracorneal ring segments. The asymmetrical implantation of the intracorneal ring segment causes inconsistent vergence change of light across the visual axis (Fig. 2A, 2B). In both cases, stromal opacities were observed. Nevertheless, other factors may contribute to the inadequate improvement in visual acuity. However, in cases of patients with a similar amount of corneal stromal opacity and thinning after infectious keratitis, sufficient visual acuity improvement was observed (Fig. 3A, 3B).
Chu et al. [15] evaluated the factors affecting clinical outcomes of correcting irregular astigmatism after radial keratotomy using scleral lenses. Their study showed that most available corneal topographic indices did not help predict visual outcomes. A uniform fluid reservoir under the scleral lens was the only significant factor affecting visual outcomes [15]. A scleral lens completely vaults the cornea and creates a fluid reservoir that contributes to the total refractive power of the tear-lens optical system. Therefore, the vergence of light caused by the fluid reservoir is increased across the cornea [16]. In case of round-shaped corneal opacity after infectious keratitis, the cornea flattens in a regular shape with the development of scarring. The tear reservoir is formed with regularity compared to those observed in severe keratoconus patients with highly irregular tear reservoir formation due to central corneal thinning and steepening. Further investigation is necessary to explore the relationship between visual improvement and regularity of the fluid reservoir.
In the present study, scleral lenses were prescribed for corneal scar and stromal opacity with phlyctenules, infectious keratitis, Peters anomaly, fibrous dysplasia, ocular graft-versus-host disease, and trauma (e.g., laceration and chemical burn). Four pediatric patients were in this group: two (9 and 11 years) with corneal opacity after traumatic corneal laceration, one (6 years) with corneal opacity due to phlyctenules, and one (9 years) with Peters anomaly. In pediatric patients, corneal transplantation is restricted because of the higher risk of surgeries such as graft rejection and postoperative inflammation [17]. Scleral lenses are reportedly a safe and helpful modality to provide good visual acuity for corneal disorders in pediatric patients [17]. The parents of all patients accepted this option to provide the best optical outcomes. All patients were well-fitted with scleral lenses, and three patients achieved visual acuity with a BLCVA of at least 0.4 logMAR. One patient with Peters anomaly was presumed to have amblyopia due to the lack of a corrective effect, a BLCVA of 1.30 logMAR, and a HCVA of 1.52 logMAR.
Eighteen eyes of 12 patients were fitted with scleral lenses due to their disability glare or monocular diplopia associated with irregular cornea astigmatism. In irregular astigmatism after refractive surgery, symptoms such as disability glare or diplopia may improve with scleral lenses [18,19]. In this study, most patients experienced improvements in these symptoms after wearing scleral lenses. However, some lacked additional visual improvement as they showed already good HCVA. Consequently, four eyes of three patients discontinued lens wear. Three eyes of two patients were usually spectacles wearers. They experienced glare, monocular diplopia, and insufficient visual acuity improvement after refractive surgery. Although these patients reported improvement in these symptoms after scleral lenses, these symptoms caused by decentralized and inhomogeneous ablation did not completely subside, and they stopped wearing the scleral lenses. Another patient who used RGP lenses had previously undergone cataract surgery with multifocal toric intraocular lenses. Although the patient’s irregular astigmatism was corrected with a scleral lens, their visual acuity did not improve due to internal astigmatism caused by intraocular lenses.
Five eyes of four patients were fitted with scleral lenses for visual rehabilitation after keratoplasty. Cornea opacity due to trauma (two eyes of two patients) and herpes keratitis (two eyes of one patient) were the most common initial diagnoses and indications for corneal transplantation. According to one study, keratoconus was the most common diagnosis for keratoplasty, and 44 eyes (91.7%) achieved functional vision with scleral lens-corrected visual acuity of 6/12 or better [20]. In our study, five eyes achieved a BLCVA of at least 0.1 logMAR.
A single trial was required for completing the fitting process. Nine eyes required refitting due to discomfort and refraction change associated with the settling phenomenon. As time elapses after wearing, the clearance decreases, the scleral alignment changes, and the so-called settling occurs [21]. Earlier studies on Jupiter scleral lens fitting reported an average of 1.5 to 3.2 lenses ordered per eye to obtain an acceptable fit [22]. The Onefit A scleral lens used in this study has a small diameter and a simple shape, so it is easier to fit in Asian patients than it is in Western populations, who use large-size scleral lenses. In addition, successful fitting was achieved by performing scleral lens fitting by one experienced ophthalmologist. To adapt the scleral lens, the scleral lens is initially worn for 5 to 6 hours a day, and the wearing time is gradually increased. If a patient drops the lens, they are instructed to immediately pick it up and clean it, as the color of the lens is slightly bluish, making it easy to find.
Most patients with corneal disorders report significant improvement in visual acuity after scleral lens fitting compared to HCVA. For patients with an irregular cornea shape, spectacles and soft contact lenses offer only limited correction of irregular astigmatism because they cannot neutralize the corneal irregularities. Previously, RGP lenses were recommended; however, in corneas with extremely steep or flat keratometry indices, traditional RGP lenses do not provide adequate centration. No alternatives were available for patients with severe keratoconus and corneal opacity except for corneal transplantation. However, this procedure entailed drawbacks, such as the lack of donor cornea, unpredictability of astigmatism, and risk of rejections [23]. In patients with severe corneal opacity and irregular astigmatism, the advantages of scleral lenses over RGP lenses are definite: a more stable and better-centered fit; no attachment to the cornea, thus avoiding exacerbation of scar formation; and greater comfortability, thereby improving quality of life [1,24].
Our study had several limitations. The main limitation was the retrospective design and relatively small sample size. Moreover, the follow-up period was relatively short. This study included various cornea disease patients, but each disease had a small sample size. Since insufficient clinical data were available for each disease, the positive effect of scleral lenses for each disease could not be determined. Further studies with larger numbers of cases for each corneal disease and a more extended follow-up period are needed to obtain more comprehensive clinical data and better understand the effects of scleral lenses in Asian patients with corneal diseases.
In conclusion, the BLCVA improved significantly following scleral lens application in various corneal diseases, with a good success rate. In addition to eyes with irregular corneal surfaces, those with opacity showed good visual acuity improvement and comfortable fitting without any adverse events. Thus, scleral lenses are a good alternative for eyes with various corneal diseases that cannot be corrected with glasses or require corneal surgeries such as keratoplasty.

Acknowledgements

None.

Notes

Conflicts of Interest: None.

Funding: None.

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Fig. 1
Horizontal anterior segment optical coherence tomography image of the left eye with scleral lens of a 30-year-old woman with keratoconus who underwent crosslinking three times. The steep K of keratometry indices on the Orbscan showed 61.0 diopters with a central corneal thickness of 332 μm. Due to the stromal opacity and failure to form a uniform fluid reservoir under the lens, the patient achieved a best lens-corrected visual acuity of 0.90 logarithm of the minimum angle of resolution with scleral lenses (uncorrected distance visual acuity, count finger; habitually corrected distance visual acuity, count finger).
kjo-2022-0164f1.jpg
Fig. 2
Scleral lens in the left eye of a 26-year-old man with keratoconus underwent crosslinking and intracorneal ring segments. The asymmetrical implantation of the intracorneal ring segment causes inconsistent vergence change of light across the visual axis. The patient achieved a best lens-corrected visual acuity of 0.52 logarithm of the minimum angle of resolution (logMAR) with scleral lenses (uncorrected distance visual acuity, 1.5 log-MAR; habitually corrected distance visual acuity, 1.3 logMAR). (A) The horizontal anterior segment optical coherence tomography image of the left eye with a scleral lens. The intrastromal ring segments are visualized. (B) The anterior segment photo of the left eye with a scleral lens.
kjo-2022-0164f2.jpg
Fig. 3
Scleral lens in the left eye of a 45-year-old woman with central corneal opacity after infectious keratitis (pseudomonas aeruginosa). Despite the central corneal opacity, the patient achieved a best lens-corrected visual acuity of 0.10 logarithm of the minimum angle of resolution (logMAR) with scleral lenses (uncorrected distance visual acuity, 1.00 logMAR; habitually corrected distance visual acuity, 0.70 logMAR). (A) The horizontal anterior segment optical coherence tomography image of the left eye with a scleral lens. Central corneal opacity with diffuse thinning was detected. (B) The anterior segment photo of the left eye.
kjo-2022-0164f3.jpg
Table 1
Baseline demographic data of the study population
Demographic No. of patients No. of eyes Age (yr) Sex (no. of patients) Laterality (no. of eyes) UCVA (logMAR)


Male Female Right Left
Keratoconus 19 (40.4) 26 (41.9) 29.90 ± 7.85 (17-45) 12 7 14 12 1.36 ± 0.85 (0.30-2.60)
Corneal scar 12 (25.5) 13 (21.0) 30.90 ± 19.80 (6-60) 4 8 8 5 1.26 ± 0.73 (0.50-2.60)
 Phlyctenules 3 3 19.00 ± 8.66 (9-24) 0 3 3 0 1.27 ± 1.15 (0.52-2.60)
 Corneal laceration 4 4 29.50 ± 20.80 (11-53) 1 3 1 3 0.75 ± 0.26 (0.49-1.00)
 Chemical burn 1 1 41 1 0 1 0 1.30
 Keratitis 1 1 60 1 0 0 1 1.30
 Peters anomaly 1 1 9 0 1 1 0 1.52
 Fibrous dysplasia 1 1 29 1 0 1 0 1.00
 GVHD 1 2 60 0 1 1 1 1.02 ± 0.71 (0.52-1.52)
Irregular astigmatism 12 (25.5) 18 (29.0) 39.60 ± 13.90 (18-72) 8 4 8 10 0.55 ± 0.60 (0-1.70)
 Refractive surgery 7 11 42.60 ± 16.10 (28-72) 4 3 5 6 0.32 ± 0.49 (0-1.70)
 PPMD 1 2 41 1 0 1 1 1.70 ± 0 (1.70-1.70)
 Monocular diplopia 4 5 34.00 ± 11.20 (18-44) 3 1 2 3 0.60 ± 0.37 (0.50-1.00)
 Penetrating keratoplasty 4 (8.5) 5 (8.1) 46.00 ± 24.00 (23-67) 3 1 2 3 1.16 ± 0.92 (0.40-2.60)
Total 47 62 33.90 ± 15.36 (6-72) 27 20 32 30 1.03 ± 0.81 (0-2.60)

Values are presented as number (%), mean ± standard deviation (range), or number only.

UCVA = uncorrected visual acuity; logMAR = logarithm of the minimum angle of resolution; GVHD = graft-versus-host disease; PPMD = posterior polymorphous corneal dystrophy.

Table 2
Comparative data for cornea astigmatic indices and lens fitting parameters
Variable Keratoconus (n = 26) Corneal scar (n = 13) Irregular astigmatism (n = 18) Penetrating keratoplasty (n = 5) Total (n = 62)
Topographic indices* (D)
 Flat K 47.3 ± 4.9 (41.7 to 59.6) 39.7 ± 6.5 (28.8 to 47.1) 39.3 ± 2.6 (34.9 to 43.1) 43.2 ± 9.5 (28.0 to 50.7) 43.0 ± 6.1 (28.0 to 59.6)
 Steep K 53.4 ± 5.9 (46.1 to 67.3) 47.6 ± 6.9 (35.8 to 54.2) 41.3 ± 3.6 (35.2 to 47.1) 50.8 ± 8.6 (36.2 to 58.6) 48.0 ± 7.4 (35.2 to 67.3)
 Astigmatism 6.1 ± 3.4 (3.0 to 13.6) 7.9 ± 3.2 (3.8 to 13.7) 2.0 ± 1.7 (0.2 to 5.8) 7.6 ± 2.9 (4.3 to 11.9) 4.9 ± 3.6 (0.2 to 13.7)
Keratometry indices* (D)
 Flat K 46.6 ± 3.0 (41.8 to 52.0) 41.0 ± 4.2 (35.8 to 47.3) 39.6 ± 2.6 (35.0 to 43.5) 44.1 ± 2.3 (40.4 to 46.2) 42.9 ± 4.0 (35.0 to 52.3)
 Steep K 53 ± 4.8 (47.0 to 62.0) 47.6 ± 4.9 (40.5 to 55.8) 41.8 ± 3.5 (35.3 to 47.0) 51.3 ± 0.8 (50.3 to 52.3) 47.4 ± 6.0 (35.3 to 62.0)
 Astigmatism 6.6 ± 2.3 (2.5 to 9.8) 6.6 ± 2.4 (3.8 to 10.0) 2.2 ± 1.9 (0.3 to 6.3) 7.2 ± 2.8 (5.5 to 11.9) 4.6 ± 3.1 (0.3 to 11.9)
Manifest refraction (SE) (D) −8.2 ± 4.5 (−16.6 to −2.0) −0.7 ± 7.1 (−7.6 to 13.0) −3.1 ± 2.0 (−7.4 to +0.3) −8.7 ± 5.6 (−13.6 to −2.5) −6.1 ± 4.6 (−16.6 to 6.4)
White-to-white (mm) 11.8 ± 0.5 (11.1 to 13.0) 11.5 ± 0.6 (10.5 to 12.3) 11.6 ± 0.5 (10.5 to 13.0) 12.0 ± 0.7 (11.1 to 13.0) 11.7 ± 0.5 (10.5 to 13.0)
Central corneal thickness (μm) 430.0 ± 57.8 (302 to 501) 490.5 ± 114.4 (337 to 592) 474.6 ± 77.5 (357 to 601) 605.4 ± 60.9 (532 to 656) 453.6 ± 76.0 (302 to 601)
Intraocular pressure (mmHg) 12.2 ± 2.8 (7 to 17) 14.5 ± 3.5 (10 to 20) 15.0 ± 4.5 (7 to 20) 16.0 ± 2.2 (13 to 19) 13.9 ± 3.7 (7 to 20)
Lens fitting parameter
 Base curve (mm) 7.56 ± 0.56 (5.8 to 8.3) 8.07 ± 0.56 (7.1 to 9.0) 8.08 ± 0.32 (7.8 to 9.0) 7.74 ± 0.34 (6.9 to 7.7) 7.80 ± 0.56 (5.8 to 9.0)
 Diameter (mm)
  14.1 1 - - - 1
  14.7 24 13 18 5 60
  14.9 1 - - - 1
 Edge
  Standard 25 11 18 5 59
  Flat 1 2 3
 Power (D) −4.97 ± 3.70 (−15.00 to 0) −0.04 ± 5.21 (−6.75 to +12.00) −4.38 ± 2.66 (−10.50 to −0.75) −3.3 ± 6.7 (−12.50 to +4.50) −3.7 ± 4.4 (−15.0 to +12.0)

Values are presented as mean ± standard deviation (range) or number of eyes.

D = diopters; K = keratometry; SE = spherical equivalent.

* Simulated K.

Table 3
UCVA, HCVA, BLCVA, and differences between UCVA and HCVA, and BLCVA and HCVA
Variable Keratoconus (n = 26) Corneal scar (n = 13) Irregular astigmatism (n = 18) Penetrating keratoplasty (n = 5) Total (n = 62)
UCVA (logMAR) 1.36 ± 0.85 (0.30 to 2.60) 1.26 ± 0.73 (0.50 to 2.60) 0.55 ± 0.60 (0 to 1.70) 1.16 ± 0.92 (0.40 to 2.60) 1.03 ± 0.81 (0 to 2.60)
HCVA (logMAR) 0.75 ± 0.79 (0.30 to 2.60) 0.82 ± 0.38 (0.30 to 1.30) 0.14 ± 0.13 (0 to 0.40) 0.84 ± 0.41 (0.40 to 1.30) 0.59 ± 0.62 (0 to 2.60)
BLCVA (logMAR) 0.12 ± 0.20 (−0.08 to 0.22) 0.21 ± 0.36 (−0.08 to 1.30) −0.01 ± 0.04 (−0.08 to 0) 0.06 ± 0.04 (0 to 0.10) 0.10 ± 0.22 (−0.08 to 2.60)
Difference between UCVA and HCVA (logMAR) 0.38 ± 0.45 0.41 ± 0.55 0.41 ± 0.56 0.32 ± 0.60 0.39 ± 0.51
p-value 0.005 0.017 0.002 0.067 <0.001
Difference between BLCVA and HCVA (logMAR) 0.63 ± 0.70 0.61 ± 0.34 0.15 ± 0.15 0.79 ± 0.41 0.50 ± 0.54
p-value <0.001 0.002 0.002 0.043 <0.001

Values are presented as mean ± standard deviation (range) or mean ± standard deviation.

UCVA = uncorrected distance visual acuity; HCVA = habitually corrected distance visual acuity; BLCVA = best lens-corrected visual acuity with scleral lenses; logMAR = logarithm of the minimum angle of resolution.

Table 4
Visual acuity before and after scleral lens fitting
Visual acuity Keratoconus (n = 26) Corneal scar (n = 13) Irregular astigmatism (n = 18) Penetrating keratoplasty (n = 5) Total (n = 62)





HCVA BLCVA HCVA BLCVA HCVA BLCVA HCVA BLCVA HCVA BLCVA
Worse than 0.4 logMAR 12 (46.2) 2 (7.7) 12 (92.3) 1 (7.7) 1 (5.6) 0 (0) 4 (80.0) 0 (0) 29 (46.8) 3 (4.8)
Better than 0.4 logMAR 14 (53.8) 24 (92.3) 1 (7.7) 12 (92.3) 17 (94.4) 18 (100) 1 (20.0) 5 (100) 33 (53.2) 59 (95.2)

Values are presented as number of eyes (%).

A visual acuity of 0.1 logMAR equals to a decimal Snellen of 0.8 and 0.4 logMAR equals to a decimal Snellen of 0.4.

HCVA = habitually corrected distance visual acuity; BLCVA = best lens-corrected visual acuity with scleral lenses; logMAR = logarithm of the minimum angle of resolution.



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