Participants
The subjects recruited for this comparative prospective study were 22 healthy children, 42 healthy adults, and 20 adults with primary open angle glaucoma (POAG). All measurements were made in the same examination room at the Hospital Clínico San Carlos, Madrid, Spain. The study protocol adhered to the principles of the Declaration of Helsinki and was approved by the clinical review board of this hospital.
Exclusion criteria were the presence of any corneal, eyelid or scleral pathology that could hinder measurements. Candidates were also excluded if they were non-cooperative. If both eyes did not meet any of the exclusion criteria, the eye to be examined was selected randomly using a web application (www.randomization.com).
Inclusion criteria for the glaucoma group were a clinical diagnosis of POAG (open angle detected on gonioscopy, IOP over 21 mm Hg on at least 3 different days, typical changes at the optic nerve head and visual field defects consistent with POAG). The healthy adult group included subjects with an IOP of 21 mm Hg or lower, no visual field defects, no other ocular diseases and no family history of glaucoma. These subjects were consecutively recruited among the hospital staff including nurses, relatives of patients, and persons visiting our clinic for a routine visual acuity examination.
Clinical measures
A comprehensive ophthalmologic examination was performed in all subjects including visual acuity testing, slit lamp biomicroscopy, fundus evaluation, central corneal thickness (CCT), axial length (AL) and IOP. CCT was measured by ultrasound pachymetry (Dicon P55; Paradigm Medical Industries Inc., Salt Lake City, UT) and AL was measured using an optical biometer (IOL Master 700, Carl Zeiss Meditec, Jena, Germany). For each participant, data were recorded including age, gender and the eye randomly selected for the study. For the patients with POAG, additional data compiled were their hypotensive treatment regimen (number of intraocular pressure-lowering drugs taken) and their latest visual field data square root of loss variance (sLV) and mean deviation (MD).
The same examiner performed all IOP measurements consecutively in a single session using the PAT (Perkins®; Clement-Clarke, Columbus, OH, USA) and Easyton® tonometers. The order of use of both devices was randomized using a web application (www.randomization.com). For the applanation tonometry, we used topical fluorescein and anesthetic, Three measurements were taken with each device and the mean of these three measures entered in the statistical analysis.
Demographic and clinical data are provided in Table 1 for each participant group: group 1 (G1) including 22 eyes of 22 healthy children of mean age of 9.7 ± 2.5 years, group 2 (G2) including 42 eyes of 42 healthy adults of mean age of 77.6 ± 10.0 years, and group 3 (G3) including 20 eyes of 20 patients with POAG of mean age 73.3 ± 9.3 years. Data for the whole group of 84 participants (G4) are also provided.
Table 1
Demographic and clinical data in the different groups of patients evaluated in the current sample.
Mean (SD)
Range
|
Children (G1) (N = 22)
|
Adults (n = 62)
|
Total (G4) (n = 84)
|
P- value*
|
Healthy subjects (G2) (n = 42)
|
Glaucoma patients (G3)
(n = 20)
|
Age (years)
|
9.69 (3.5)
5–13
|
77.6 (10.0)
61–95
|
73.3 (9.3)
61–86
|
56.1 (32.1)
5–95
|
< 0.001
|
Transpalpebral IOP (mm Hg)
|
14.6 (2.5)
9–18
|
15.5 (2.0)
8–21
|
15.6 (4.0)
10–31
|
15.3 (2.7)
9–30
|
0.231
|
PAT IOP (mm Hg)
|
14.13 (2.19)
9–17
|
15.36 (2.09)
8–23
|
17.25 (4.06)
13–28
|
15.49 (2.90)
9–28
|
0.002
|
AL (mm)
|
22.76 (1.11)
20.89–25.10
|
23.51 (1.50)
21.16–30.58
|
24.08 (1.89)
21.76–26.56
|
23.42 (1.56)
20.89–30.58
|
0.013
|
CCT (µm)
|
545.8 (39.4)
492–662
|
542.8 (38.9)
472–637
|
550.4 (38.1)
496–632
|
545.4 (39.0)
456–687
|
0.780
|
MD (dB)
|
-
|
-
|
6.7 (6.8)
-1.5-22.9
|
-
|
|
sLV (dB)
|
-
|
-
|
4.7 (2.1)
1.5–8.3
|
-
|
|
Ocular medication (drops)
|
-
|
-
|
1.6 (1.4)
0–4
|
-
|
|
Abbreviations: SD, standard deviation; IOP, intraocular pressure; CCT, central corneal thickness; AL, axial length; MD, mean deviation; sLV, square root of loss variance |
*Result of the comparison between G1, G2 and G3. |
Statistical analysis
All statistical tests were performed using SPSS software version 12.0 for Windows (SPSS Inc., Chicago, IL, USA) and MedCalc 7.3. The Kolmogorov–Smirnov test was used to check the normality of the distribution of quantitative data. Normally distributed data were compared using the Student’s t-test and Pearson’s r coefficient of correlation and non-normally distributed data with the Mann Whitney nonparametric test and Spearman’s r coefficient. Individual groups were compared through one-way analysis of variance (ANOVA) and the Kruskal-Wallis test for normally and non-normally distributed data variables respectively. Post-hoc Bonferroni adjustment was used to correct for the effect of multiple comparisons. To assess agreement between the two tonometers, we calculated intraclass correlation coefficients (ICC). The Bland-Altman method was used to graphically depict the level of agreement between the Easyton© and Perkins© IOP measurements for the whole sample. Significance was set at p < 0.05.