The Effect of Corneal Biomechanical Factors on Ocular Pulse Amplitude in Normal Subjects

Han Jo Kwon; Ji Woong Lee; Jong Hun Shin

doi:10.3341/jkos.2015.56.8.1248

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Kwon, Lee, and Shin: The Effect of Corneal Biomechanical Factors on Ocular Pulse Amplitude in Normal Subjects

Original Article

J Korean Ophthalmol Soc 2015;56(8):1248-1255.

Published online: 29 August 2015

DOI: https://doi.org/10.3341/jkos.2015.56.8.1248

The Effect of Corneal Biomechanical Factors on Ocular Pulse Amplitude in Normal Subjects

Han Jo Kwon, M.D., Ji Woong Lee, M.D., Jong Hun Shin, M.D.

Department of Ophthalmology, Pusan National University Hospital, Pusan National University School of Medicine, Busan, Korea

Address reprint requests to Jong Hun Shin, MD Department of Ophthalmology, Pusan National University Hospital, #179 Gudeok-ro, Seo-gu, Busan 602-739, Korea Tel: 82-51-240-7326, Fax: 82-51-242-7341 E-mail: jjongggal@naver.com

∗ This work was supported by clinical research grant from Pusan National University Hospital 2010.

Received 9 January 201519 February 2015 Accepted 19 June 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To investigate the influence of corneal biomechanical factors on ocular pulse amplitude measured using dynamic con-tour tonometry in normal subjects.

Methods

The study population consisted of normal subjects who visited the outpatient clinic from January, 2014 to July, 2014. Ocular pulse amplitude was measured using dynamic contour tonometry and corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using an ocular response analyzer. We applied univariate and multivariate linear regressions to in-vestigate the relationship between ocular pulse amplitude and corneal biomechanical factors and other ocular factors.

Results

Fifty eyes of 50 patients (average age 52.8 ± 17.2 years) were examined. The average ocular pulse amplitude was 2.90 ± 1.04 mm Hg and the CH and CRF were 10.44 ± 1.96 mm Hg and 11.03 ± 2.21 mm Hg, respectively. In univariate linear re-gression, factors influencing ocular pulse amplitude were ocular pressure based on CRF (β = 0.280, p = 0.049), Goldmann ap-planation tonometry (β = 0.293, p = 0.039), and spherical equivalent (β = 0.283, p = 0.047), while in multivariate linear regression the only factor influencing ocular pulse amplitude was CRF (β = 0.686, p = 0.042).

Conclusions

A positive correlation between ocular pulse amplitude reflecting ocular perfusion pressure and CRF reflecting cor-neal elasticity was observed. Correlations between the 2 factors will be an important aspect in future studies regarding the influ-ences of corneal biomechanical factors on ocular perfusion pressure in glaucoma patients.

Keywords: Corneal biomechanical factors, Dynamic contour tonometry, Ocular pulse amplitude

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Figure 1.

(A) Scatterplot showing the correlation between intraocular pressure (IOP) measurements obtained by Goldmann applana-tion tonometer (x-axis) and dynamic contour tonometry (y-axis) (R = 0.826, p < 0.001). (B) Generalized Bland-Altman plot of the agreement between Goldmann applanation tonometer IOP measurements and dynamic contour tonometry measurements. The differ-ence between the measurements (y-axis) is plotted against the average of the measurements (x-axis). Dash-dotted lines represent 95% limits of agreement. The difference between two methods was regressed on the average of the two methods (dash line) (R = 0.357, p = 0.011). DCT = dynamic contour tonometry; GAT = Goldmann applanation tonometer.

Figure 2.

(A) Scatterplot showing the correlation between intraocular pressure (IOP) measurements obtained by Ocular response an-alyzer IOPcc (x-axis) and dynamic contour tonometry (y-axis) (R = 0.751, p < 0.001). (B) Generalized Bland-Altman plot of the agreement between Goldmann applanation tonometer IOP measurements and Ocular response analyzer IOPcc measurements. The difference between the measurements (y-axis) is plotted against the average of the measurements (x-axis). Dash-dotted lines repre-sent 95% limits of agreement. The difference between two methods was regressed on the average of the two methods (dash line) (R = 0.004, p = 0.978). DCT = dynamic contour tonometry; IOPcc = corneal-compensated intraocular pressure.

Table 1.

Clinical and ocular biochemistric characteristics of the normal and ocular hypertension patients

Parameters	Data
Number of patients (eyes)	50 (50)
Male:female (n)	21:29
Age (years)	52.8 ± 17.3 (16-76)
Sex (male: female)	53.1 ± 14.6 (16-76):
	52.2 ± 20.8 (16-76)
SE (diopters)	-0.93 ± 1.58
Axial length (mm)	23.67 ± 1.17 (21.41-25.63)
CCT (μ m)	555.68 ± 35.14 (483.0-630.0)
GAT (mm Hg)	17.14 ± 3.09 (10.0-24.0)
IOPcc (mm Hg)	17.60 ± 3.82 (10.8-24.1)
DCT (mm Hg)	20.19 ± 3.83 (12.7-27.7)
OPA (mm Hg)	2.90 ± 1.04 (1.3-6.1)
CH (mm Hg)	10.44 ± 1.96 (5.5-16.0)
CRF (mm Hg)	11.03 ± 2.21 (6.7-16.4)

Values are presented as mean ± SD (range) unless otherwise indicated. SE = spherical equivalent; CCT = central corneal thickness; GAT = Goldmann applanation tonometry; IOPcc = corneal-compen-sated intraocular pressure; DCT = dynamic contour tonometry; OPA = ocular pulse amplitude; CH = corneal hysteresis; CRF = corneal resistance factor.

Table 2.

Pearson correlation coeffecient between OPA and var-ious ocular parameters, including corneal biomechanical fac-tors and intraocular pressure with dynamic contour tonometer, Goldmann applanation tonometer, and Ocular Response Analyzer in normal subjects

Parameters	R	p-value
GAT (mm Hg)	0.293	0.039
IOPcc (mm Hg)	0.247	0.084
DCT (mm Hg)	0.241	0.091
CH (mm Hg)	0.116	0.421
CRF (mm Hg)	0.280	0.049
CCT (μ m)	0.063	0.676
Axial length (mm)	-0.191	0.296
SE (diopter)	0.283	0.047
Age (years)	0.002	0.789

OPA = ocular pulse amplitude; R = Pearson correlation coefficient; GAT = Goldmann applanation tonometry; IOPcc = corneal-com-pensated intraocular pressure; DCT = dynamic contour tonom-etry; CH = corneal hysteresis; CRF = corneal resistance factor; CCT = central corneal thickness; SE = spherical equivalent.

Table 3.

Results of multiple linear regression analysis with ocular pulse amplitude as dependent and various ocular parameters in-cluding IOP measurements obtained with Goldmann applanation tonometer (Model 1), ocular response analyzer (Model 2), and dy-namic contour tonometer (Model 3) as explanatory variable in normal subjects

		β^∗	p-value^†
Model 1	CRF	0.686	0.042
Model 2	CRF	0.686	0.042
Model 3	CRF	0.686	0.042

All models were adjusted for age, corneal hysteresis, axial length, spherical equivalent, and IOP measurements. IOP = intraocular pressure; CRF = corneal resistance factor.

^∗ Standardized coefficient;

^† By backward method.

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