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Purpose: Study the correlations between corneal geometry (Pentacam) and biomechanical (ORA) properties with morphology

The study of the correlations of the optic disc size with Cornal Geometry and Biomechanical characteristics Fernanda B Fonyat,MD Renata Siqueira, MD; Guilhermo C Velarde, DSc Renato Ambrosio Jr, MD, PhD.

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Purpose: Study the correlations between corneal geometry (Pentacam) and biomechanical (ORA) properties with morphology

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  1. The study of the correlations of the optic disc size with Cornal Geometry and Biomechanical characteristics Fernanda B Fonyat,MDRenata Siqueira, MD; Guilhermo C Velarde, DScRenato Ambrosio Jr, MD, PhD Purpose: Study the correlations between corneal geometry (Pentacam) and biomechanical (ORA) properties with morphology of the disc optic size (HRT)

  2. Introduction • Corneal properties represent independent risk factors for Glaucoma neuropathy • Ocular Hypertension Treatment Study (OHTS ) and European Glaucoma Prevention Study Group ( EGPS) demonstrated that low thickness of cornea is a important predictive factor for ocular hypertensive patients develop glaucoma lesion in the optic nerve • A relation between geometrical and biomechanical properties of the cornea and optic nerve susceptibility may exist • Cornea and sclera wall have same embryologic origin, thereby the cribriform lamina of the optic disc may share similarities with the cornea whose measurements may be able to anticipate higher impact of pressure on the optic nerve

  3. Introduction • Ocular Response Analyzer (ORA, Reichert) is a non contact air pulse pressure measurement that dynamically measures corneal properties • Corneal hysteresis, cornea resistant factor (CRF), intra-ocular pressure for Goldman (IOPg) and intra-ocular pressure compensate (IOPcc) • Congdon et al identify that hysteresis reduction is a negative factor to perimetry • Pentacam have a specific software that analyze the paquimetry progression with is better than measure just the central thickness of the cornea • Lesk et al showed with Heidelberg Retina Tomography (HRT) a biggest complacence of cribriform lamina in patients with thin cornea

  4. Ocular Response Analyzer (ORA, Reichert) Measurement • Corneal response to a collimetric air pulse is monitored by the infrared light reflection (applanation => peak) • Detects two applanation events correlated with the air pulse pressure (INWARD - p1 and OUTWARD - p2) • The delay of p2 is caused by corneal viscous damping • [CH = p1 – p2] and [CRF = p1 - (K * p2)] • Normal Values: CH: 10.17 ± 1.82 (3.23 to 14.58) CRF: 10.14 ± 1.8 (5.45 to 15.1) • IOPg: 15.24 ± 3.8 (7.45 to 25.8) • IOPcc: 15.97 ± 3.8 (7.63 to 26.1) ORA Signal

  5. Corneal Tomography (CTm) (Pentacam, Oculus) • Patented 360º Scheimpflug camera that captures 25 to 50 corneal slits • Normal Values (n=200 normal corneas): • Pachy Thinnest: 541 ± 33.2 (438 to 611) • Corneal volume (4mm): 11.44 ± 0.67 (9.3 to 12.9) • Keratometric Astigmatism: 1.2 ± 0.97 (0 to 6.9) • Pachymetric Progression (maximal): 1.1 ± 0.2 (0.6 to 1.9)

  6. Patients and Methods • Retrospective study in patients who did Pentacam, HRT and ORA. All patients where Caucasian and they didn’t have ocular disease or refractive surgery • The retinography was classify as Disc Damage Likelihood Scale (DDLS) • The statistic test was SPSS v 13.0. For IOP g , CRF and hysteresis were used Pearson’s test and for IOPcc Spearman’s test

  7. Results • 75 patients were female and 47 were male • 244 eyes from 122 patients were analyzed • The mean age was 47,2 (8 to 97 years with sd 21,7) • There was no statistical significant correlation between optic disc size and intra-ocular pressure • There were statistical significant correlations between optic disc size and biomechanical and geometrical characteristics of the cornea ; Optic disc size x CRF Significant negative correlation r=-0.1337 (p=0.0263) Optic disc size x thinnest paquimetry

  8. Results • There was a significant negative correlation between CRF, hysteresis (CH), thinnest corneal value, Pachymetric Progression Index on the Maximal axis and corneal volume • There were a significant positive correlation between optic disc size and astigmatism and axis Optic disc size x Corneal volume (4mm), Significant correlation r=-1.887 (p=0.0017) Optic disc size x astigmatism axis Significant correlation r=-0.1766(p=0.0034) Optic disc size x greatest paquimetry progression

  9. Example: Thick cornea

  10. Example: Thin cornea

  11. Discussion • We found a negative association between corneal geometric and biomechanical parameters and morphology of the optic disc • This study was limited because some patients were treated with glaucoma medications and because functional tests such as perimetry were not analyzed Conclusion • There is a negative correlation between optic disc and corneal characteristics, which can explain in part why the cornea is a important risk factor to increase • Such data may lead to susceptibility parameters for glaucoma neuropathy development.

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