The purpose of this recent retrospective study was to compare visual outcomes between mini-scleral lenses (SLs) and small-diameter rigid GP (RGP) lenses in individuals who have moderate-to-severe keratoconus (KC).¹ Additionally, the clinical utility of corneal topographic indices in guiding lens selection was evaluated.

The study included 36 eyes from 28 patients who had moderate to severe KC. Sixteen males and 12 females with a mean age of 35.33 years (95% confidence interval: 31.77–38.90 were included in the study. All eyes in the SL group had mild apical scarring.

The study was performed between May 2017 and January 2024, with a mean follow-up period of 468 days. Data collected included patient demographics, daily lens wearing time, visual analog scale (VAS) scores, best-corrected visual acuity (BCVA), keratometry, location of the cone, and corneal topographic indices. Multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were used to identify predictors of lens selection and visual improvement.

The RGP group was fit with a HLK fitting set comprised of 29 diagnostic lenses with base curves from 4.8 to 7.6 mm (0.1 mm increments). The standard “3-point touch” technique was used for lens fit.²

Optimal fluorescein patterns were characterized by apical contact, midperipheral bearing, and good lens centration. Individuals who were intolerant of GP lenses or those who had apical scarring were fit with SLs. Fluorescein staining was used for SL fitting. An ideal scleral lens fit was characterized by central clearance (50 mm to 100 mm), adequate edge lift, and absence of conjunctival blanching.

RGP lenses were fitted on 30 eyes from 24 patients. SLs were fit on 6 eyes from 4 patients who had apical scars. Both groups demonstrated significant improvement in BCVA after lens fitting. Eyes fit with RGPs had significantly lower surface regularity index, cone-to-center distance, and irregular astigmatism index (IAI), but a higher center-surround index (CSI) compared to eyes fit with SLs.

Keratometry values significantly decreased following RGP lens wear. Lower CSI values were associated with greater visual improvement. ROC analysis indicated that higher IAI values and more eccentric cone locations predicted better suitability for mini SLs, whereas higher CSI supported RGP lenses. VAS scores were comparable between groups; however, RGP lens wearers reported longer daily wear time.

Topographic indices are widely used for the diagnosis of KC and the early detection of subclinical disease. However, their role in predicting visual improvement and RGP lens fitting outcomes in moderate-to-severe KC has been less well studied. This study demonstrated that lower CSI was associated with better visual outcomes, suggesting that cone location may be more influential than corneal steepness in predicting success with RGP lenses. These findings support the incorporation of topographic indices such as CSI, IAI, and cone-to-center distance into contact lens fitting algorithms. This approach may assist practitioners in selecting the most appropriate lens type, particularly for individuals who have moderate-to-severe KC.

BCVA is significantly improved with both small-diameter RGP and mini SLs in moderate to severe KC. SLs are particularly advantageous for eyes with apical scarring or highly decentered cones. Topographic indices such as CSI and IAI serve as valuable pre-fitting predictors, helping guide lens type selection and anticipate visual improvement. These indices could be incorporated into fitting software or clinical decision-support tools, further enhancing clinical strategies for contact lens fitting.

This study is limited by its retrospective design, short follow-up, and small sample size, particularly in the SL group (n=6), which may reduce statistical power and model stability. Since the study was performed at a tertiary referral center, advanced KC may be overrepresented. Additionally, apical scarring in all mini-SL eyes may have contributed to lower baseline visual acuity, greater post-fitting improvement, and potential selection bias affecting keratometric and topographic interpretation. 

References

1. Chang EC, Kuo CJ, Lee SH, Hou YC. Comparison of visual acuity outcomes and topographic differences: rigid gas-permeable lens versus mini-scleral lenses for moderate-to-severe keratoconus. Taiwan J Ophthalmol. 2025. doi: 10.4103/tjo.TJO-D-25-00084

2. Leung KK. RGP fitting philosophies for keratoconus. Clin Exp Optom. 1999;82:230-235. doi: 10.1111/j.1444-0938.1999.tb06653.x

Melissa Barnett, OD, FAAO, FSLS, practices at Baker Optometry. She has received remuneration from ABB, AbbVie, Alcon, Azura, Bausch + Lomb, BCLA, Bruder, Cloudbreak Pharma, Dompé, Epion, OCuSOFT, ScienceBased Health, STAPLE Program, Tarsus, and Théa Pharma.

 This content was supported via unrestricted sponsorship