Abstract
Purpose:
To analyze the changes in corneal aberrations induced by different combinations of triangular section ICRS in keratoconic eyes
Methods:
86 keratoconic eyes were evaluated with Scheimpflug tomography (Pentacam by Oculus) before and three months after ICRS implantation (Ferrara-type, triangular section). Corneal aberrations were estimated by virtual ray tracing on anterior and posterior corneal elevation maps, using Zemax, in a 4-mm area centered in the eye’s pupil. Eyes were divided in groups according to the combination (1 or 2) , geometry (optical zone diameter, OZ, 5 or 6 mm, and ICRS angle, 90, 60, 160, 210 deg); and location (inferior I or superior S) of implanted ICRS: 1-OZ5-160I (6 eyes); 2-OZ5-160I-90S (6 eyes); 1-OZ5-210I (5 eyes) ; 2-OZ6-120I-90S (5 eyes) : 2-OZ6-120I-120S (14 eyes); 2-OZ6-150I-90S (8 eyes); 1-OZ6-150I (19 eyes); 1; OZ6; 210I (8 eyes). Changes in corneal aberrations were analyzed by group.
Results:
On average ICRS decreased corneal astigmatism by 43% (p<0.001) and corneal coma by 18% (p=0.056). However trefoil increased by ~20% and the overall amount of HOA did not decrease significantly. 5 mm OZ ICRS overall tended to reduce HOA by 39,4% (p=0.09), on average changing coma from 1.23±0.54 μm preop to 0.84±0.50 μm postop (p<0.05), and astigmatism from -5.4±2.6 D preop to -3.5±2.4 D postop (p<0.05). 6 mm OZ ICRS decreased corneal astigmatism (from -5.79±3.17 D preop to -3.14±2.11 D postop; p<0.001) but did not systematically decrease other aberrations. Across groups, coma decreased substantially in 1-OZ5-160I and 1-OZ5-210I (by 21.7% and 39,3%, respectively) and slightly in 2-OZ6-120I-120S (by 12.7%) but increased in 2-OZ6-120I-90S (by 2,9%). Conversely, astigmatism decreased significantly (p<0.05) in the last two groups (by 72,8% and a 55,4% respectively).
Conclusions:
Estimations of corneal aberrations in patients implanted with ICRS allows evaluation of the optical changes, rather than corneal shape alone. 5 mm OZ ICRS decrease efficiently corneal aberrations. While 6 mm OZ ICRS produce the largest improvement of astigmatism. Understanding the relationships between ICRS geometry /implantation pattern and the change in optical aberrations is crucial to refine nomograms.