Abstract
Purpose :
To investigate whether stress distribution patterns can predict biomechanical progression in keratoconus (KCN) eyes using longitudinal data.
Methods :
The corneal contribution to stress, CCS=r/2t, was calculated based on the Hoop stress formula without intraocular pressure. Here r is radius of curvature and t is corneal thickness, thus CCS exhibits greater stress with lower corneal thickness or flatter curvature. We calculated CCS from Pentacam curvature and thickness maps (Oculus, Wetzlar, Germany) and investigated the difference in the magnitude of stress between the 2-mm zones of the CCSmin and CCSmax, ΔCCS, and the distance between these 2 zones, ΔCCSdistance. We included patients with diagnosed KCN and healthy controls. Exclusion criteria were use of contact lenses, previous corneal surgery, including corneal crosslinking, corneal scar, other corneal diseases and bad quality of Pentacam images. We investigated if ΔCCS and ΔCCSdistance changed over time and used a mixed linear model approach to determine if ΔCCS at baseline could predict keratoconus progression.
Results :
A total of 111 eyes of 67 KCN patients and 31 eyes of 31 healthy controls were included with a mean age of 25±7 and 24±4 years, respectively. KCN patients had a mean follow-up time of 566 days (range: 28 to 1720 days). At baseline, in KCN eyes mean greatest stress was 8.3±1.0 (range 5.8 to 11.3± 1) and lowest stress was 6.6±0.6 (range 4.9 to 8). For healthy eyes mean values were 7.4±0.5 (range 6.4 to 8.4) and 6.5±0.5 (range 5.6 to 7.6) respectively. ΔCCS significantly increased over time (p<0.001) and correlated significantly with zonal Kmax (r=0.82, p<0.001) (Fig. 1). ΔCCS at baseline predicted progression over time of zonal Kmax (p=0.007). ΔCCSdistance correlated significantly with ΔCCS (r=-0.33, p<0.001), but did not change in time (p=0.42).
Conclusions :
The difference between the minimum and maximum stress contribution, ΔCCS, changes in time and its baseline values predict progression in keratoconus patients. We did not find a change in the distance between the highest and lowest stress area over time.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.