Fluid reservoir thickness and aberration relationship in keratoconic eyes with scleral lenses

Abstract

Purpose To investigate the effect of varying the fluid reservoir (FR) thickness of scleral lenses (SL) on corrected distance visual acuity (CDVA), contrast sensitivity (CS) and higher‐order aberrations (HOAs) in keratoconic eyes. Methods Forty eyes with keratoconus were fitted with a diagnostic Boston Sight SL having three different FR thicknesses. CDVA, CS and HOAs were measured before and after 30 min of lens wear. An i‐Trace aberrometer and anterior segment optical coherence tomography (AS‐OCT) were used to measure HOAs and FR thickness, respectively. Results Statistically significant improvements in CDVA and CS were seen with different FR thickness lenses (p < 0.01). Baseline CDVA (0.22 ± 0.15) improved to 0.03 ± 0.06, 0.04 ± 0.07 and 0.07 ± 0.08 with low, standard and high FR lenses, respectively. Post‐hoc testing showed better CDVA with low (p = 0.006) and standard FR (p = 0.009) lenses compared to high FR lenses. Before lens wear, CS was 1.27 ± 0.27, which improved to 1.67 ± 0.11, 1.73 ± 0.12 and 1.66 ± 0.89 with low, standard and high FR lenses, respectively. Lenses with standard FR showed better CS compared with those having low (p = 0.009) and high FRs (p < 0.001). A statistically significant reduction of higher order‐root mean square aberrations (HO‐RMS), coma, spherical aberration, secondary astigmatism and trefoil were found with all FR thickness lenses compared to baseline (p < 0.01). No significant difference was noted between lenses (p = 0.01). All three lenses corrected almost equal amount of HOAs. A moderate positive correlation was observed between CDVA and HO‐RMS (r = 0.61, p < 0.001) for low FR lenses. Conclusions BostonSight SCLERALs were found to be very effective in improving vision, CS and reducing HOAs in keratoconus. Lenses with varying FR thickness showed equal effectiveness in visual performance and reducing HOAs. FR thickness should be considered an important factor to provide better vision and CS by minimising HOAs, as well as to maintain the normal physiology of eyes with keratoconus.

Impact of Scleral Lens Front Surface Eccentricity on Visual Acuity, Contrast Sensitivity, and Higher-Order Aberrations in Eyes With Keratoconus

“…CS has been considered a very sensitive assessment for visual disturbances because of a higher amount of HOAs 28 and the Pelli–Robson CS test as a standard measuring tool to quantify visual performance in keratoconus eyes. 29 The current study reported reduced baseline CS, which was consistent with the previous studies, 20 and showed noticeable improvement with all three lenses with different eccentricities in keratoconus corneas, which were in comparison with the previous studies. 17,18 Present studies have reported better CS with FSE1 and FSE2 when compared with FSE0 but were not clinically or statistically significant and showed a difference of only two or 3 letters in the Pelli–Robson chart.…”

“…SL tilt and decentration secondary to improper haptic alignment 9,35 and higher FRT 8 are related to HOAs by inducing a significant amount of aberrations. Contrary to these results, Balakrishnan et al 20 found no significant impact of higher FRT on HOAs. In the current study, all these lenses were trial lenses from the diagnostic set, although the authors did not report any significant amount of tilt or decentration clinically, the measurements over final patient lenses could have yielded a better result by avoiding lens tilt and decentration, which need further analysis.…”

“…The amount of HOAs has a fundamental role in visual performance in keratoconic eyes, and the presence of a greater amount of HOAs has been reported in the previous literature, which was consistent with this study. 16,20,31 The impact of SLs on correcting HOAs has already been well established. 2,3,16,20,32 Earlier pieces of evidence have reported a greater impact of FSE values of SLs in correcting HOAs.…”

“…16,20,31 The impact of SLs on correcting HOAs has already been well established. 2,3,16,20,32 Earlier pieces of evidence have reported a greater impact of FSE values of SLs in correcting HOAs. 2,[16][17][18] While experiencing the role of eccentricity, Hussoin et al 18 have explained various mechanisms on how eccentricity improves vision in corneal ectatic patients.…”

“…The lens details have been explained in a previous study. 20 The current study lenses were of 18.5 mm diameter, made from Boston Equalens II material (Oprifocon A) of 85 Dk, center thickness of 300 mm, and with different FSE values of FSE0 (0.00), FSE1 (0.30), and FSE2 (0.60) with the standard sagittal height and standard haptic lens. SLs from a diagnostic trial set were used.…”