Introduction

Dry eye disease (DED) is a common ocular disorder with a global prevalence rate of approximately 10%, with the highest rates reported in East Asia1. Its prevalence is expected to rise with an aging global population2,3; however, studies have also indicated that DED is increasingly affecting younger individuals4.

Corneal irregularities can lead to uneven tear distribution, tear film instability, and increased tear evaporation5. Patients with keratoconus (KC) are more prone to DED than healthy individuals6, exhibiting a shorter tear break-up time (TBUT) and lower tear meniscus height7.

Clinically, contact lenses—including bandage contact lenses and scleral contact lenses (SCLs)—are used to alleviate dry eye symptoms. Improve visual acuity in patients with corneal irregularities while also protecting the ocular surface and stabilizing the tear film8.

Owing to these advantages, SCLs are increasingly recognized as an important therapeutic option for managing irregular astigmatism with DED. However, their large diameter requires saline instillation to form a corneal tear reservoir during wear, and an excessively thick tear lens may cause corneal hypoxia9,10. Meanwhile, conjunctival asymmetry can affect the fitting of SCLs10. Mini-scleral lenses (mSLs) are easier to handle and are better suited for patients with small palpebral fissures, shortened fornices, or localized scleral elevations than standard SCLs11,12. Studies have shown that small-diameter lenses combined with the smallest corneal gap can promote optimal corneal health condition and provide better corneal oxygen supply13, leading to expanded clinical indications for mSLs.

Several studies have compared visual improvement between SCLs and rigid gas-permeable lenses (RGP)14, and they also reported the use of SCLs in treating ocular surface disease15. However, few comparative studies have evaluated the efficacy of mSLs versus RGP in treating irregular astigmatism with DED. To address this gap, this prospective randomized controlled trial aimed to systematically compare visual acuity correction, dry eye parameters, ocular surface characteristics, and complication rates in patients fitted with mSLs versus RGP, and to analyze both objective findings and subjective symptoms of dry eye to provide evidence for clinical treatment choices and strategies.

Methods

Participants

This single-blind (examiner-blind) prospective pilot randomized controlled study enrolled 50 patients (98 eyes) with irregular corneas at Tianjin Eye Hospital between August 2021 and May 2023. The study cohort consisted of 28 males and 22 females. The inclusion criteria were as follows: age ≥ 18 years and corneal astigmatism ≥ 0.75 diopters (D) from any cause (including KC, irregular cornea, or corneal transplantation). The corneal topography examination shows that astigmatism has lost symmetry and presents as various shapes (deviated hourglass shape, tongue-like spread and irregular hourglass shape, island shape, etc.). Patients also demonstrated objective signs of DED (Non-Invasive TBUT < 10 s; OSDI-6 ≥ 4; Ocular surface staining assessment revealed more than five corneal punctate stains, more than nine conjunctival punctate stains, and eyelid margin staining ≥ 2 mm in length and ≥ 25% in width); along with corresponding symptoms confirmed on ocular surface examination. The exclusion criteria were as follows: (1) active corneal infections or other ocular diseases (e.g., glaucoma, chronic uveitis, vitreous hemorrhage, maculopathy, or retinal vascular disease); (2) ocular conditions unsuitable for contact lens wear (e.g., abnormal endothelial cell density, use of medications affecting corneal curvature, or monophthalmia); (3) systemic diseases incompatible with contact lens wear or patients have poor adherence; (4) unsuitability for rigid contact lenses based on corneal parameters, shape, and diopter;  and (5) poor tolerance or compliance. A total of 40 patients (78 eyes) were ultimately included for subsequent analysis, with a follow-up completion rate of 80.00%. Patient information is presented in Table 1. Information on patients lost to follow-up is presented in Table 2. The research process is shown in Fig. 1.

Table 1 Medical and surgical histories of the patients.
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Table 2 Information of patients lost to follow-up.
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Fig. 1
Fig. 1
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Flow diagram.

Design

Participants who met the inclusion criteria were randomized into the mSLs group (18 patients, 35 eyes; mSLs, model: KTSL; Tianjin Century Kangtai Biomedical Engineering Co., Ltd, China) and the RGP group (22 patients, 43 eyes; RGP, model: XO; Opcom Technology Co., Ltd, China). mSLs are made of fluorosilicone acrylate polymer with high oxygen permeability, The specific material used was Boston XO2, with an oxygen permeability of 141 × 10− 11 (cm2/s) (mL O2/mL × mmHg). The material of RGP was Boston XO, with an oxygen permeability of 100 × 10− 11 (cm2/s) (mL O2/mL × mmHg).

Randomization was performed using block randomization with a block size of 4. The randomization sequence was completed using an online randomization tool (www.sealedenvelope.com), and the sequence was made into envelopes and kept by a third-party researcher who was not involved in the study. After the patient enrollment, the researcher of this project informed the third-party researcher to open the envelopes in sequence to determine each patient’s group allocation. The study protocol was approved by the Hospital Clinical Trial Review Ethics Committee (Approval No.: TJYYLCSYSCLL-2022-16 and TJYYLCSYSCLL-2023-04) and registered on ClinicalTrials.gov (Identifier: NCT06256770; Date: 02/05/2024). This study was conducted in accordance with the principles of the Declaration of Helsinki. All participants provided written informed consent. For statistical analysis, one eye per patient was selected according to a predefined rule: the eye with better baseline visual acuity was included, with the right eye selected in the event of equal acuity.

Sample size was estimated using G*Power 3.1 for the primary endpoint OSDI. Using f = 0.40, α = 0.05, power = 0.80, two groups, five time points, and a repeated-measures correlation of r = 0.60, the required sample size was N = 36. A total of 40 participants completed the study, meeting the calculated requirement.

All patients received relevant evaluations from professional ophthalmologists before contact lenses fitting and study inclusion as follows: (1) systemic and ocular history documentation, including ophthalmic surgery and use of ocular medications; (2) ophthalmic examination, including slit-lamp microscopy (S359, MediWorks, Shanghai, China), non-contact tonometry (Canon TX-20, Saitama Prefecture, Japan), corneal endothelial cell count (Konan SP-8000, Yokkaichi, Japan), corneal topography (Pentacam HR, Oculus, Germany), and fundus photography, to exclude contraindications such as glaucoma, fundus disease, or active inflammation; and (3) visual acuity assessments, including UCVA, BSCVA, and CLCVA. Based on these assessments, eligible patients were enrolled and randomly fitted with either mSLs (KTSL) or RGP lenses (XO). Although multiple ophthalmologists participated in preliminary eligibility screening, one masked examiner performed all baseline and follow-up outcome evaluations used for analysis following a uniform standardized protocol to ensure consistency and minimize inter-observer variability.

Assessment

After enrollment, participants were followed up at 1 week, 1 month, 3 months, and 6 months after lens fitting. During the follow-up process, the examiner remained blinded to the type of lenses worn by the patients. All measurements were taken 3 times and averaged. Assessments included:

1. Objective assessments.

(1) corrected lens corrected visual acuity (CLCVA): At a distance of 5 m, visual acuity was measured using a projected standard logarithmic visual acuity chart that randomly displayed a single E visual target. If the largest visual target still cannot be seen clearly at a distance of 5 m, you need to move forward until the visual target is recognized.

(2) tear film break-up time (TBUT): TBUT was measured when the patient was not wearing contact lenses using a comprehensive ocular surface examination device (OCULUS Keratograph, Germany).

(3) slit-lamp biomicroscopy: this was performed to evaluate lens fit. The mSL diameter was set 3.5 mm larger than the patient’s horizontal visible iris diameter (HVID), and the landing area was designed to smoothly adhere to the sclera without local compression or lifting. The fit assessment was conducted after wearing the lens and again after 2 h of settling. The RGP base curve was equal to or less than the patient’s the flat K value on corneal topography. The diameter of the lens was set 1.4 mm smaller than HVID, and the fitting of the lens should be evaluated 5 min after wearing the lens. If the fit was relatively tight or loose, the base curve or the optical zone diameter was adjusted accordingly. Lens fit was assessed at each follow-up time point using slit-lamp biomicroscopy according to the following criteria: (1) centration deviation: the deviation between the optical center of the lens and the center of the cornea was ≤ 0.2 mm; (2) range of motion: after the patient blinks, the vertical range of motion of the lens on the corneal surface was expected to be 0.5–1.2 mm; (3) microscopic bubbles: no sub-lens bubbles or tiny bubbles not exceeding Grade 1 were permitted between the lens and cornea (defined as occasional, isolated and very small bubbles); and (4) fluorescein pattern: under cobalt blue light after applying a fluorescein sodium ophthalmic strips (Tianjin Jingming New Technological Development Co., Ltd., China) wet with sodium chloride (Otsuka Pharmaceutical Co., Ltd., China) to the conjunctiva, the staining pattern was assessed. mSLs should show uniform bright staining across the cornea. RGP lenses were expected to show uniform, light central staining with a 0.2–0.3 mm non-compressive peripheral tear accumulation band (indicating a three-point touch fit).

(4) Anterior segment optical coherence tomography (AS-OCT, Tomy, Japan) was used to measure tear thickness under the mSLs. The ideal tear reservoir depth at the corneal vertex of mSLs was generally ≤ 1/2 corneal thickness, and the tear layer thickness at the limbus position was ≤ 1/4 corneal thickness.

(5) Corneal topography: In keratoconus, corneal topography showed a centrally steepened cornea with thinning at the steepest point. The curvature difference between the lower and upper parts of the cornea exceeded three dimension. Corneal topography in patients with irregular corneas showed disordered and irregular color distribution, with complete loss of symmetry.

2. Subjective symptom assessments:

Subjective symptoms were assessed using Chinese questionnaires, completed with the assistance of examiners during the investigation. The OSDI was used to evaluate grade dryness and visual quality, while the CLDEQ-8 was employed to assess lens-specific discomfort and dryness severity. The visual fluctuation survey was included in the OSDI and CLDEQ-8 questionnaires.

(1) The Ocular Surface Disease Index (OSDI)16.

OSDI is a tool used to screen and diagnose patients with dry eye. It assesses the severity of dry eye. It contains 12 questions and 3 parts, including ocular symptoms, visual function, and environmental triggers. The higher the OSDI index value, the more severe the ocular surface lesions.

  1. (1)

    (2) The Contact Lens Dry Eye Questionnaire-8 (CLDEQ-8)17.

CLDEQ-8 is a questionnaire specifically designed to assess dry eye symptoms in contact lens wearers. It covers the eight most relevant symptom items and is the best-validated tool closest to measuring contact lens-related discomfort.

(3) Visual fluctuation.

The OSDI and CLDEQ-8 questionnaires both include items assessing visual fluctuations. During the investigation process, patients reporting visual fluctuations were asked about their frequency, severity and occurrence time. Subsequently, scores were assigned. The higher the score, the more severe the degree of vision fluctuation and blurred vision. The proportion of patients who experienced vision fluctuations and blurred vision at each time point was ultimately tallied.

The OSDI and visual fluctuations were assessed at baseline and at 1-week, 1-month, 3-month, and 6-month follow-ups. Blurred vision was evaluated daily at 8:00 a.m., 12:00 p.m., 4:00 p.m., and 8:00 p.m. The CLDEQ-8 was assessed at 1-week and 1-, 3-, and 6-month follow-ups. On both scales, lower scores indicated better ocular comfort and quality of life.

Statistical analysis

Data analysis was performed using IBM SPSS Statistics for Windows, version 27.0 (IBM Corp. Armonk, NY, USA). Continuous variables were evaluated for data normality by the Shapiro–Wilk test and homogeneity of variance using the Levene’s tests. Repeated measures ANOVA were used to analyze visual acuity, TBUT, OSDI score, and CLDEQ-8 score, visual fluctuation. If the sphericity hypothesis was met, Bonferroni-adjusted post hoc comparisons were performed when P < 0.05. If the spherical assumption was violated, the Greenhouse–Geisser correction was applied. If homogeneity of variance was not met, the Friedman test and corresponding post hoc analysis were used. The comparison of adverse reactions between the two groups was conducted using the chi-square (χ2) test. The lens fitting was analyzed using one-way ANOVA. The significance level of all statistical tests was set at P < 0.05.

Results

Ultimately, 40 participants completed the experiment. The average age of the patients was 27.9 ± 6.62 years (95% confidence interval [CI], 25.81 to 30.04). The mean spherical equivalent was − 3.86 ± 4.23 D in the right eye (95% CI -5.61 to -2.11) and − 3.81 ± 4.48 D in the left eye (95% CI -5.66 to -1.96). The mean astigmatism was − 2.30 ± 2.90 D in the right eye (95% CI -3.33 to -1.28) and − 2.68 ± 2.15 D in the left eye (95% CI -3.44 to -1.91). No significant differences were observed between the two groups in age, refractive error, or corneal topography (Table 3). All dropouts were included in the intention-to-treat analyses, and no withdrawals were attributed to serious adverse events.

Table 3 Age, diopter, and corneal topography values of the two groups of patients.
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Objective assessments

Visual acuity

All visual acuity measurements were converted to logMAR values for analysis, with lower values indicating better visual acuity.

Repeated measures analysis of variance (ANOVA) was used to compare differences in ∆VA (uncorrected visual acuity [UCVA] − contact lens-corrected visual acuity [CLCVA]) between the two groups. Since the sphericity assumption was violated, the Greenhouse–Geisser correction was adopted. The results demonstrated that the RGP group showed greater ∆VA than the mSLs group, with significant differences at all four follow-ups (P = 0.022, η2p = 0.079; P = 0.019, η2p = 0.084; P = 0.022, η2p = 0.079; and P = 0.017, η2p = 0.085) (Table 4). No significant difference was observed in ∆VA changes between the groups over the follow-up period (F = 0.473, P = 0.683, η2p = 0.082, ε = 0.908, Greenhouse–Geisser correction).

Table 4 Comparison of the differences between UCVA and CLCVA in the mSLs/RGP group.
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Using the Friedman rank sum test, CLCVA was significantly better than best spectacle-corrected visual acuity (BSCVA) at all follow-ups in both groups (mSLs: χ2 = 55.2, both P < 0.001; RGP: χ2 = 48.5, P = 0.01, P < 0.001, P = 0.002, and P < 0.001) (Fig. 2).

Fig. 2
Fig. 2
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The differences between BSCVA and CLCVA in the two groups at each follow-up. BSCVA best spectacle-corrected visual acuity, VA visual acuity; *significant differences; **: very significant differences; ***: extremely significant differences.

TBUT

Repeated measures ANOVA showed that TBUT was significantly higher in the mSLs group than in the RGP group at 1-week (F = 5.110, P = 0.028, η2p = 0.096), 1-month (F = 16.362, P < 0.001, η2p = 0.254), and 3-months (F = 6.778, P = 0.012, η2p = 0.124) (Fig. 3).

Fig. 3
Fig. 3
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The TBUT of the mSLs group and the RGP group. Lower Edge of the Box (Q1): The first quartile (25th percentile). Line Inside the Box (Q2): The median (50th percentile). Upper Edge of the Box (Q3): The third quartile (75th percentile). Lower Whisker End: The minimum data value within the range (Q1–1.5 * IQR). Upper Whisker End: The maximum data value within the range (Q3 + 1.5 * IQR). ns: Not Significant; *: Significant differences; ***: extremely significant differences.

Differences were observed in TBUT between the two groups during the four follow-ups (F = 7.380, P < 0.001, η2p = 0.133, Mauchly W = 0.89, spherical correction). The Bonferroni test revealed statistically significant differences between baseline(mean = 5.5) and the 1-week (mean = 7.7, P < 0.001), 1-month (mean = 7.3, P = 0.002), and 3-months (mean = 7.3, P = 0.003) follow-ups. Additionally, significant differences were observed between the 1- and 6 months (mean = 6.9, P = 0.009) follow-ups in the mSLs group. Statistically significant differences were noted between baseline (mean = 6.3) and the 1-week(mean = 7.5, P = 0.002) and 1-month (mean = 5.2, P = 0.009) follow-ups. Significant differences were also found between the 1-week and 1-month(P < 0.001) and 3-months (mean = 6.1, P < 0.001) follow-ups, as well as the 1- and 6-month (mean = 6.9, P < 0.001) follow-ups in the RGP group.

Lens fit

In the mSLs group, AS-OCT measurements showed a post-lens tear fluid thickness of 251.86 ± 97.40 μm at 1 week and 289.30 ± 79.44 μm at 6 months representing a 14.9% increase. No statistically significant difference was observed between 1-week and 6-months follow-ups (P = 0.08).

Subjective symptom assessments

Ocular surface disease index (OSDI) scores

The OSDI scores of the two groups were analyzed using repeated measures ANOVA. Since the sphericity hypothesis was not valid, the Greenhouse–Geisser correction method was used for analysis. The OSDI scores decreased over time in both groups. At 3-months (F = 11.484, P = 0.002, η2p = 0.270) and 6-months (F = 12.155, P = 0.001, η2p = 0.282), OSDI scores were significantly lower in the mSLs group than in the RGP group (Fig. 4).

Fig. 4
Fig. 4
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The OSDI scores of the mSLs group and the RGP group. Lower Edge of the Box (Q1): The first quartile (25th percentile). Line Inside the Box (Q2): The median (50th percentile). Upper Edge of the Box (Q3): The third quartile (75th percentile). Lower Whisker End: The minimum data value within the range (Q1–1.5 * IQR). Upper Whisker End: The maximum data value within the range (Q3 + 1.5 * IQR). ns: not significant. **: very significant differences; ***: extremely significant differences.

Fig. 5
Fig. 5
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The CLDEQ-8 scores of the mSLs group and the RGP group. Lower Edge of the Box (Q1): The first quartile (25th percentile). Line Inside the Box (Q2): The median (50th percentile). Upper Edge of the Box (Q3): The third quartile (75th percentile). Lower Whisker End: The minimum data value within the range (Q1–1.5 * IQR). Upper Whisker End: The maximum data value within the range (Q3 + 1.5 * IQR). ns not significant; *significant differences.

Differences were noted in OSDI scores between the two groups (F = 41.174, P < 0.001, η2p = 0.570, ε = 0.706, Greenhouse–Geisser correction). in the mSLs group, the Bonferroni test revealed that OSDI scores progressively decreased from baseline (mean = 33.1) to the 1- (mean = 24.0, P < 0.001), 3- (mean = 19.2, P < 0.001), and 6-months follow-ups (mean = 17.6, P < 0.001), Significant reductions were also observed between the 1 week (mean = 28.3) and at 1- (P = 0.022), 3- (P < 0.001), and 6-months (P < 0.001)follow-ups, as well as between the 1-month and 3-, 6-months (all P < 0.001) follow-ups. In the RGP group, the OSDI score continued to decrease from baseline (mean = 32.8) to 1-week (mean = 29.8, P = 0.048), 1 month (mean = 28.0, P < 0.001), 3-months (mean = 26.2, P < 0.001), and 6-months (mean = 25.0, P < 0.001) follow-ups. Significant differences were also noted between 1 week and at 3-months (P = 0.017) and 6-months (P = 0.004) follow-ups.

Contact lens dry eye questionnaire-8 (CLDEQ-8) scores

The CLDEQ-8 scores of the two groups were analyzed through repeated measures ANOVA. Since the sphericity assumption was violated, the Greenhouse–Geisser correction was adopted. The mSLs group demonstrated lower scores than the RGP group at each follow-up, and CLDEQ-8 scores decreased during the follow-up period in both groups. Between-group comparisons indicated that the mSLs group had significantly lower scores than the RGP group at 1-month (F = 4.964 ,P = 0.033, η2p = 0.131), 3-months (F = 4.158, P < 0.049, η2p = 0.112), and 6-months (F = 6.247, P = 0.018, η2p = 0.159) (Fig. 5).

Significant differences were observed in CLDEQ-8 scores between the two groups (F = 16.813, P < 0.001, η2p = 0.338, ε = 0.656, Greenhouse–Geisser correction). In the mSLs group, the Bonferroni test showed that all follow-up comparisons were significantly different except between 1 week and 1 month (P = 0.055). In the RGP group, no significant differences were observed between 1-week and 1-month (P = 0.562) or between 3-months and 6-months (P = 0.276). In contrast, all other timepoints showed significant changes.

Visual fluctuations

The visual fluctuation between the two groups were compared using repeated measures ANOVA. Significant differences were observed in visual fluctuations between the two groups (F = 30.393, P < 0.001, η2p = 0.884, Mauchly W = 0.022, spherical correction). Between-group comparisons showed that the mSLs group had significantly fewer visual fluctuations than the RPG group at 1-month (F = 12.991, P = 0.023, η2p = 0.765), 3-months (F = 23.194, P = 0.009, η2p = 0.853), and 6-months (F = 28.347, P = 0.006, η2p = 0.876). Visual fluctuations of the two groups are shown in Fig. 6.

Fig. 6
Fig. 6
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The visual fluctuations of the mSLs group and the RGP group. ns: not significant; *significant differences.

In the mSLs group, the Bonferroni test showed that all timepoints differed significantly except between 6-months and 1-week (P = 0.087), and between 3-months and 6-months (P = 0.134). In the RGP group, visual fluctuations at 6-months differed significantly from those at 1-week, 1-month, and 3-months (P = 0.037, P = 0.019, P = 0.040, respectively).

Figure 7 shows the degree of two groups of blurred vision. Blurred vision occurred when wearing mSLs and RGP. Throughout the day, the degree of blurred vision increased with longer wearing time.

Fig. 7
Fig. 7
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The degree of blurred vision of the mSLs group and the RGP group.

Complications

No adverse events were severe and led to trial withdrawal. Slit-lamp microscope evaluations at each follow-up documented the following mild ocular complications: Three cases of mild limbal neovascularization were observed—one in the mSLs group and two in the RGP group—with all presenting as 0.5 × 0.5 mm limbal fan-shaped pannus. In the mSLs group, one case of mild ciliary congestion, and one case of mild corneal epithelial injury were recorded. The incidence of adverse events was 12.5%. All events occurred within the first month and resolved after adjusting lens parameters or using medication. All patients who experienced adverse reactions were treated with 0.3% sodium hyaluronate eye drops (Santen Pharmaceutical Co., Ltd, Japan) and 0.1% fluorometholone eye drops (Santen Pharmaceutical Co., Ltd, Japan) four times daily for 7 days. The difference in adverse event rates between the groups was not statistically significant (Yates’ continuity correction for continuity, P = 0.81).

Discussion

Recently, mSLs have been increasingly used to manage irregular corneal and ocular surface diseases18,19,20. mSLs have also been shown to improve corrected visual acuity in patients with irregular corneas18. Therefore, this study further explored their effect in alleviating dry eye symptoms.

This study demonstrated that the best corrected visual acuity was better with both mSLs and RGP than with BSCVA, including nine patients after corneal transplantation. Moreover, both scleral lenses and RGP lenses are rigid contact lenses. Both can correct the irregularity of the corneal surface by taking advantage of the smooth posterior surface of the lens to improve vision21,22. This effect may be related to the large diameter and high-vault design of SCLs, which avoids contact with suture zones after corneal transplantation and provides more stable visual quality19. Severinsky found that patients who had undergone corneal transplantation and failed other contact lens treatments had improved vision and better tolerance to SCLs23. RGP can also reduce the spherical aberration and astigmatic aberration, thereby improving the best corrected visual acuity after corneal transplantation24. In the results, the ∆VA (UCVA–CLCVA) in the mSLs group was lower than that in the RGP group. This might be related to factors, including the sample size limitation in the study, individual ocular surface characteristics, lens adaptation, wearing compliance, and lens care habits. It does not necessarily indicate superior visual performance of RGP.

Patients with irregular corneas due to their irregular ocular surface epithelium may have unstable tear films and activated of stress signaling pathways, triggering inflammatory responses and contributing to DED25. Corneal transplantation can further disrupt ocular surface homeostasis, leading to reduced corneal sensitivity, decreased blink frequency, increased fluorescein staining, and shorter TBUT26. Moreover, corneal transplantation reduces corneal sensitivity and decreases the number of blink attacks, leading to signs and symptoms of DED36. Additionally, some specific inflammatory mediators may be expressed in certain irregular astigmatic corneas (such as keratoconus) and dry eye syndrome27. Dry eye syndrome also increases the irregularity of the corneal epithelium28. The two form a vicious circle. TBUT is a important criterion for evaluating the tear film stability and an important objective indicator in dry eye examinations29. In irregular corneas, tear film quality declines, making it more prone to tear film instability and leading to the occurrence of dry eye syndrome30,31.

Over the 6-month follow-up, TBUT increased in both groups. However, the comparison of TBUT at not all follow-up time points was statistically significant. The increase in TBUT at each follow-up in the mSLs group was not significant, and in the RGP group, it also decreased during the follow-up period. The TBUT alone may not fully represent complex ocular surface changes or determine the efficacy of the two contact lens types in improving ocular surface conditions. Further analyze is needed to analyze the effects of mSLs and RGP on improving the ocular surface environment through subjective investigations of patients’ dry eye conditions.

The OSDI and CLDEQ-8 score showed a decreasing trend with time after treatment in both groups, indicating that both mSLs and RGP had improved the comfort of the ocular surface to a certain extent. At 6 months follow-up, the OSDI and CLDEQ-8 scores were lower in the mSLs group than in the RGP group, with the mSLs group demonstrating lower CLDEQ-8 scores at each follow-up. This indicates that mSLs may provide better improvement in the subjective symptoms of dry eye in patients than RGP, and this result has important clinical significance. Although the TBUT index did not improve significantly in this study, the improvement of subjective symptoms after wearing mSLs suggests that mSLs are suitable for patients whose subjective symptoms of dry eye are dominant. Additionally, Levit research found that after wearing SCLs, both the comfort and visual perception of the supervisor were superior to those of RGP32.

However, both mSLs and RGP experienced visual fluctuations. As the contact lens wearing time increased, the proportion of individuals with visual fluctuations in both groups decreased. This might be related to the increased adaptation of the patient’s ocular surface to contact lenses. Meanwhile, the proportion of individuals with visual fluctuations in the mSLs group at the 1-, 3-, and 6-month follow-ups was lower than that in the RGP group. We consider that the reason for this difference may be related to the movement of RGP in the ocular surface. Although patients can adapt to RGP lens movement, they cannot fully eliminate the instability of the lens. Further studies are needed to clarify this reason.

The incidence of blurred vision throughout the day (daily blurred vision) in both group increased with longer wearing time. In mSLs, this phenomenon, known as mid-day fogging, is caused by the accumulation of particulate matter, including lipids and inflammatory cells, in the tear reservoir. This is more common in patients with DED10,19. In RGP, extended wear time may cause hypoxia and osmolarity changes, which can also lead to blurred vision33.

This kind of mild blurred vision is not a contraindication for wearing contact lenses. It can be improved by using high-Dk RGP materials34, limiting wearing time35, filling the tear reservoir of SCLs with high-viscosity, ion-containing and preservative-free artificial tears, temporarily removing and reapplying the lens, or modifying the lens fit36.

Three patients in the RGP group switched to mSLs during follow-up. Subsequently, they all reported better comfort, reduced foreign body sensation, and fewer vision fluctuations when using mSLs. One patient felt that the visual fluctuation of mSLs was smaller, and RGP wearers were more prone to blurred vision. This may indicate that patients with irregular corneas may experience greater subjective comfort and feeling with mSLs. This may be due to reduced mechanical friction between the edge of mSLs and the sensitive limbal nerve plexus37. Rigid corneal contact lenses, such as RGP, may repeatedly rub against the limbal region during blinking. This may potentially damage limbal stem cells and lead to complications, including limbal edema, corneal neovascularization, persistent epithelial defects, and corneal conjunctivalisation, namely limbal stem cell deficiency (LSCD)38,39. Martin reported that many patients with long-term contact lens wear developed LSCD despite having no prior ocular disease, with the superior limbus being particularly vulnerable40. Beyond mechanical irritation, prolonged hypoxia associated with RGP wear stimulates interaction between inflammatory cells and angiogenic factors, promoting limbal neovascularization and impairing limbal function41. SCLs are large-diameter, rigid gas-permeable lenses that completely vault the cornea42,43,44. Studies have shown that SCLs exhibit less limbal contact, reducing the risk of epithelial injury and providing greater comfort45. Therefore, SCLs may contribute to help manage LSCD and prevent limbal complications46. Schornack reported a patient in whom contact lens-induced LSCD was successfully treated using a scleroscope47. Kim used PROSE scleral lenses to improve the ocular surface conditions of at least 10 patients with contact lens-induced LSCD48.

Notably, vertical movement of RGP during blinking may trigger a protective blink-suppression reflex, increasing the rate of incomplete blinking. This may exacerbate abnormalities in meibomian gland lipid secretion and worsen dry eye symptoms49,50,51. The stable fit of mSLs may help restore the physiological blink cycle, which could explain the significant improvement in “dry eye discomfort and foreign body sensation” observed in the CLDEQ-8 scores of the mSLs group. Meanwhile, the continuous accumulation of tears beneath the mSLs creates a moist microenvironment that reduces corneal epithelial exposure and dryness, thereby enhancing comfort. This may explain why mSLs are better than RGP in alleviating subjective symptoms.

Although the incidence of microbial keratitis in SCLs users is low, and significant corneal edema is rare during daily wear, the risk of infection remains a serious consideration51. While no severe adverse events occurred in this study, complication rates did not differ significantly between groups. As the population of scleral lens wearers grows, vigilant monitoring is essential. Although severe, vision-threatening corneal edema is rare during daily wear, subclinical hypoxic effects may develop slowly over time10. More comprehensive, long-term studies are needed to fully understand the safety profile of modern scleral lenses.

This study had some limitations. First, the sample size was small, with a single-center design. No more detailed grouping was conducted based on the severity of corneal irregularities. Moreover, the 6-month follow-up period was relatively short, and we did not further assess the changes in corneal endothelial cell counts after wearing the lenses. Patients were aware of their type of contact lenses, which may have affected their subjective comfort. Assessing dry eye symptoms mainly relies on subjective questionnaires, which cannot systematically evaluate the long-term ocular surface condition and stability after wearing contact lenses. For patients with such complex corneal morphology and ocular surface conditions, long-term follow-up and additional measures—including contrast sensitivity, higher-order aberrations, and scattering index—are needed to fully assess differences in real-life visual quality of mSLs and RGP. Second, in this study, the thickness of the tear layer in the mSLs group increased by 14.9% at the 6-months follow-up compared to the 1-week follow-up, as measured using AS-OCT. Since this indicator was not measured in the RGP group, these data cannot strongly indicate whether the tear film of patients wearing mSLs is more stable than of those wearing RGP. Finally, due to the limitations of clinical examinations, more objective dry eye tests  (including corneal staining, Schirmer test, or tear osmotic pressure) were not conducted. More detailed grading scale evaluations (such as CCLRU or Efron) were also not conducted in the slit lamp examination section. These measures could serve as indicators for subsequent research.

In addition to exploring the uses of scleral lenses themselves, their combined use with other treatment methods can also be regarded as a future research. Studies have demonstrated that SCLs can serve as an effective medium for drug delivery, facilitating better transportation of drugs to the cornea and enhancing the therapeutic effect of the drugs51. Lee et al.46 found that the combined use of contact lenses and autologous serum can effectively treat chronic corneal epithelial defects and reduce recurrence. Therefore, future research should investigate whether supplementing the aqueous layer with dry eye medications, including sodium hyaluronate eye drops, can further improve the DED.

In conclusion, this study indicates that mSLs have the effect of improve the best corrected visual acuity in patients with irregular corneas, and also play a positive role in alleviating the subjective symptoms of dry eye and the comfort of the ocular surface in patients with irregular corneas. However, larger-scale research is needed in the future to further explore the advantages of the two contact lenses in clinical practice.