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Authors: Leonidas Traipe Ines Cayuqueo Fabiola Cerfogli Claudia Goya Allister Gibbons. Biomechanical Properties of the Cornea in Normal-Tension Glaucoma. The authors have no financial interest. Universidad de Chile. Fundación Oftalmológica los Andes. Purpose/Objectives.
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Authors: Leonidas Traipe Ines Cayuqueo Fabiola Cerfogli Claudia Goya Allister Gibbons Biomechanical Properties of the Cornea in Normal-Tension Glaucoma The authors have no financial interest Universidad de Chile. Fundación Oftalmológica los Andes.
Purpose/Objectives • To evaluate corneal Hysteresis (CH), Corneal resistance factor (CRF), Corneal Compensated IOP (ccIOP) and Goldman type IOP (gIOP), in patients with the diagnosis of normal-tension glaucoma.
Materials/Methods • We analyzed 49 eyes of 26 patients seen in our center. 22 (84.6%) of patients were female. The total sample had on average 68 ± 9.9 years. • We identified the patients through the retrospective revision of clinical charts, and posteriorly examined them between March and July of 2008. • The patients were examined with the Reichert Ocular Response Analyzer and Ultrasonic Pachimetry (CCT).
Inclusion Criteria • • Confirmed Diagnosis of Normal-Tension Glaucoma (NTG) • • IOP < 21 mmHg with the Goldman aplanation Tonometer in all examinations without treatment • • Open Angle determined by gonioscopy • • Typicall glaucomatous optic disc damage, excavation size, notch, etc. • • Visual Field Defect compatible with the Optic Nerve Defect • • No previous intraocular surgery • Exclusion Criteria • • IOP > 21 mmHg with the Goldman aplanation Tonometer in any examination without treatment • • Corneal ectasia • • Contact lens user • • Pregnancy
Results / CH R = 0.763 p<0.0001 R = 0.554 p<0.0001
Results / CRF R = 0.761 p <0.0001 R = 0.649 p <0.0001
R = 0.407 p < 0.004 • Practically no correlation (r = 0.407). • This means aproximately only 16.6% of ccIOP could be explained by the CRF (R2 = 0,166)
Results / gIOP R = 0.902 p <0.0001 R = 0.434 p < 0.002
R = 0.182 p < 0.19 • ccIOP and CCT do not seem to be governed by a linear relantionship. Either: • There is no relationship • The relationship is more complex
ccIOP was significantly higher than the gIOP. The average difference was 2.01 mmHg
Conclusions • In our sample of NTG patients, Corneal Compensated IOP was higher than goldman simulated IOP - Approximately 2 mmHg. • Corneal Resistance Factor: • Correlated positively with gIOP (R=0,76) • Correlated poorly with ccIOP (R=0,41) • There was a strong correlation between Corneal Hysteresis and Corneal Resistance Factor.
Conclusions • In our study population, our results differed from expected in that: • We found some correlation between Corneal Hysteresis and Corneal Resistance Factor with the Central Corneal Thickness. • There seems to be none or poor correlation between gIOP or ccIOP with Central Corneal Thickness. • This could be explained in part because: • We used a diseased population. • We studied a population (chilean) for which we have no normal values calculated.