Correlation between apical protrusion in the Scheimflug imaging and Corneal Hysteresis and Corneal Resistance factor by Ocular Response Analyzer, among refractive non-keratoconic Egyptian patients
Introduction: Apical protrusion in the central 4-mm ring in the Scheimflug imaging (Pentacam), both for the anterior and posterior floats as well as Corneal Hysteresis and Corneal Resistance Factor by Ocular Response Analyzer (ORA), generally are considered important predictors for post-Lasik ecta...
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| Format: | Article |
| Language: | English |
| Published: |
Electronic Physician
2015-10-01
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| Series: | Electronic Physician |
| Subjects: | |
| Online Access: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4623802/ |
| Summary: | Introduction: Apical protrusion in the central 4-mm ring in the Scheimflug imaging (Pentacam), both for the
anterior and posterior floats as well as Corneal Hysteresis and Corneal Resistance Factor by Ocular Response
Analyzer (ORA), generally are considered important predictors for post-Lasik ectasia. The aim of this work was
to find out if there is a statistically significant correlation between these different predictors and their correlation
with the central corneal thickness for refractive non-keratoconic Egyptian patients trying to achieve a better
decision and avoiding ectasia.
Methods: This case-control study involved 142 eyes (of 77 patients with various refractive errors) arriving at the
refractive surgery unit in the Research Institute of Ophthalmology in Giza (Egypt) in 2014-2015 seeking excimer
laser ablation. The flattest, steepest keratometry readings, central corneal thickness as well as the apical
protrusion in the central 4-mm ring, both for the anterior and posterior floats, in microns were measured by
Scheimflug imaging. The Corneal Hysteresis and Corneal Resistance Factor were measured by the ocular
response analyzer. Statistical analysis was performed by SPSS, using the Pearson correlation test.
Results: The spherical refractive error ranged from +7.00 to -13.00 diopters (-3.80 ± 2.89). The central
pachymetry ranged from 494 to 634 µm (550.35 ± 32.13). For the central 4-mm ring, the apical protrusion ranged
from 0 to +15 µ (6.93 ± 2.99) for the anterior float and from -3 to +20 µ (9.33 ± 4.55) for the posterior float. The
Corneal Hysterisis (CH) ranged from 7 to 14.8 mmHg (10.18±1.44), while the Corneal Resistance Factor (CRF)
ranged from 7.5 to 14.9 mmHg (10.58 ± 1.67). There was a strong positive correlation between the central
corneal thickness and both Corneal Hysteresis (CH: r = 0.56, P ≤ 0.01) and Corneal Resistance Factor (r = 0.46, P
≤ 0.01). A significant correlation (P < 0.05, r = 0.15) existed between apical protrusion in the posterior float and
the central corneal thickness. Also, significant negative correlation (P < 0.05, r = -0.12) existed between apical
protrusion in the anterior float by pentacam and the Corneal Resistance Factor by ocular response analyzer.
Conclusions: Our finding of a strong positive correlation between both Corneal Hysteresis and Corneal
Resistance Factor and the Central corneal thickness being important for biomechanical corneal stability. The
findings of this study also support using both machines preoperatively to decrease the risk of post-Lasik ectasia. |
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| ISSN: | 2008-5842 2008-5842 |