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Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer.
Invest Ophthalmol Vis Sci 2006; 47(12):5337-47IO

Abstract

PURPOSE

The Ocular Response Analyzer (ORA) is a new instrument that measures the corneal biomechanical response (corneal hysteresis, CH) to rapid indentation by an air jet. CH is the difference in applanation pressures (P1, P2) between the rising and falling phases of the air jet. The investigation had two parts: a characterization study and a validation study. In the characterization study, the purposes were to investigate the intraocular pressure (IOP)-dependence of CH and to characterize the performance of the ORA. In the validation study, the purposes were to investigate the association between CH and both age and central corneal thickness (CCT) and the agreement between ORA and Goldmann applanation tonometer (GAT) IOP measurements.

METHODS

For the characterization study, data were collected from 105 untreated subjects (45 ocular hypertensive patients and 60 normal subjects; mean age, 60 years, range, 26-82). GAT and ORA measurements were performed before and after IOP lowering of one randomly selected eye with apraclonidine drops. The change in P1 and P2 (arbitrary units) in relation to change in GAT IOP was analyzed to calibrate the instrument. The relation between P1, P2, and CCT was explored and ORA IOP was derived from the analyses. For the validation study, ORA and GAT IOP and CCT were measured in 144 eyes of 144 untreated subjects (mean age, 58 years; range, 19-83). The characterization calculations were applied to the dataset and values of CH and ORA IOP were calculated. The relationship between CH and both subject age and CCT was determined. The associations between CH and CCT and between ORA and GAT IOPs, were investigated by linear regression analysis. The agreement between measuring devices was calculated.

RESULTS

In the characterization study, P1 changed by 6.41 arbitrary units for every 1-mm Hg change in GAT IOP. CH (P1 - P2) changed by -1.60 arbitrary units for every 1-mm Hg change in GAT IOP. For each unit change in P2, P1 changed by 1.27 units. From this association a new IOP-independent corneal factor was derived [P1 - (P2/1.27)] and is termed the corneal constant factor (CCF; mm Hg). ORA IOP normalized for CCF was defined as P2 - CCF (mm Hg). The CCF (mm Hg) was associated with CCT (micrometers) and with age: CCF = [(0.036 . CCT) - (0.028 . age)] + 1.06 (adjusted r2 = 0.34; P < 0.0001 for CCT, P = 0.007 for age). Normalized ORA IOP measurements were not associated with CCT. GAT IOP was associated with CCT and CCF-more strongly with the latter: GAT IOP = (0.03 . CCT)+1.52 (r2 = 0.06, P = 0.002); GAT IOP = (0.65 . CCF) + 4.5 (r2 = 0.13, P < 0.0001). The mean difference (95% limits of agreement) between GAT and normalized ORA IOP was 0.1 (-6.6 to +6.8) mm Hg.

CONCLUSIONS

The CCF describes an IOP-independent biomechanical property of the cornea that increases with thicker CCT and decreases with greater age. It is moderately strongly associated with CCT and yet explains more of the interindividual variation in GAT IOP than does CCT. Normalized ORA IOP measurements are not associated with CCT.

Authors+Show Affiliations

Glaucoma Research Unit, Moorfields Eye Hospital, London, United Kingdom.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Validation Studies

Language

eng

PubMed ID

17122122

Citation

Kotecha, Aachal, et al. "Corneal Thickness- and Age-related Biomechanical Properties of the Cornea Measured With the Ocular Response Analyzer." Investigative Ophthalmology & Visual Science, vol. 47, no. 12, 2006, pp. 5337-47.
Kotecha A, Elsheikh A, Roberts CR, et al. Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer. Invest Ophthalmol Vis Sci. 2006;47(12):5337-47.
Kotecha, A., Elsheikh, A., Roberts, C. R., Zhu, H., & Garway-Heath, D. F. (2006). Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer. Investigative Ophthalmology & Visual Science, 47(12), pp. 5337-47.
Kotecha A, et al. Corneal Thickness- and Age-related Biomechanical Properties of the Cornea Measured With the Ocular Response Analyzer. Invest Ophthalmol Vis Sci. 2006;47(12):5337-47. PubMed PMID: 17122122.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Corneal thickness- and age-related biomechanical properties of the cornea measured with the ocular response analyzer. AU - Kotecha,Aachal, AU - Elsheikh,Ahmed, AU - Roberts,Cynthia R, AU - Zhu,Haogang, AU - Garway-Heath,David F, PY - 2006/11/24/pubmed PY - 2007/2/3/medline PY - 2006/11/24/entrez SP - 5337 EP - 47 JF - Investigative ophthalmology & visual science JO - Invest. Ophthalmol. Vis. Sci. VL - 47 IS - 12 N2 - PURPOSE: The Ocular Response Analyzer (ORA) is a new instrument that measures the corneal biomechanical response (corneal hysteresis, CH) to rapid indentation by an air jet. CH is the difference in applanation pressures (P1, P2) between the rising and falling phases of the air jet. The investigation had two parts: a characterization study and a validation study. In the characterization study, the purposes were to investigate the intraocular pressure (IOP)-dependence of CH and to characterize the performance of the ORA. In the validation study, the purposes were to investigate the association between CH and both age and central corneal thickness (CCT) and the agreement between ORA and Goldmann applanation tonometer (GAT) IOP measurements. METHODS: For the characterization study, data were collected from 105 untreated subjects (45 ocular hypertensive patients and 60 normal subjects; mean age, 60 years, range, 26-82). GAT and ORA measurements were performed before and after IOP lowering of one randomly selected eye with apraclonidine drops. The change in P1 and P2 (arbitrary units) in relation to change in GAT IOP was analyzed to calibrate the instrument. The relation between P1, P2, and CCT was explored and ORA IOP was derived from the analyses. For the validation study, ORA and GAT IOP and CCT were measured in 144 eyes of 144 untreated subjects (mean age, 58 years; range, 19-83). The characterization calculations were applied to the dataset and values of CH and ORA IOP were calculated. The relationship between CH and both subject age and CCT was determined. The associations between CH and CCT and between ORA and GAT IOPs, were investigated by linear regression analysis. The agreement between measuring devices was calculated. RESULTS: In the characterization study, P1 changed by 6.41 arbitrary units for every 1-mm Hg change in GAT IOP. CH (P1 - P2) changed by -1.60 arbitrary units for every 1-mm Hg change in GAT IOP. For each unit change in P2, P1 changed by 1.27 units. From this association a new IOP-independent corneal factor was derived [P1 - (P2/1.27)] and is termed the corneal constant factor (CCF; mm Hg). ORA IOP normalized for CCF was defined as P2 - CCF (mm Hg). The CCF (mm Hg) was associated with CCT (micrometers) and with age: CCF = [(0.036 . CCT) - (0.028 . age)] + 1.06 (adjusted r2 = 0.34; P < 0.0001 for CCT, P = 0.007 for age). Normalized ORA IOP measurements were not associated with CCT. GAT IOP was associated with CCT and CCF-more strongly with the latter: GAT IOP = (0.03 . CCT)+1.52 (r2 = 0.06, P = 0.002); GAT IOP = (0.65 . CCF) + 4.5 (r2 = 0.13, P < 0.0001). The mean difference (95% limits of agreement) between GAT and normalized ORA IOP was 0.1 (-6.6 to +6.8) mm Hg. CONCLUSIONS: The CCF describes an IOP-independent biomechanical property of the cornea that increases with thicker CCT and decreases with greater age. It is moderately strongly associated with CCT and yet explains more of the interindividual variation in GAT IOP than does CCT. Normalized ORA IOP measurements are not associated with CCT. SN - 0146-0404 UR - https://www.unboundmedicine.com/medline/citation/17122122/Corneal_thickness__and_age_related_biomechanical_properties_of_the_cornea_measured_with_the_ocular_response_analyzer_ L2 - http://iovs.arvojournals.org/article.aspx?doi=10.1167/iovs.06-0557 DB - PRIME DP - Unbound Medicine ER -