Intraocular pressure monitoring by rebound tonometry in children with myopia

Abstract

Background/purpose: Topical atropine treatment is generally accepted to retard the progression of myopia, but it is associated with side effects such as photophobia and elevation of intraocular pressure (IOP). IOP measurements in children are challenging. The traditional applanation tonometry by direct contact with the cornea will require patient's cooperation. The rebound tonometer, using a dynamic electromechanical method for measuring IOP, shows good correlation with traditional tonometry. The purpose of this study is to evaluate the IOP of myopic children under atropine treatment using rebound tonometer and to compare the characteristics between rebound tonometry and applanation tonometry.

Methods: This study is a prospective study measuring IOP by rebound tonometer in myopic children under regular low-dose atropine treatment. We recruited children with refraction error showing myopia over -0.5 D with 0.15%, 0.3%, or 0.5% atropine eye drops use every night or every other night for myopia control. Children with treatment duration of atropine <1 month were excluded from the study. IOP measurements were performed by applanation tonometer (Tono-Pen XL, Reichert) and rebound tonometer (ICARE). The reliability of rebound tonometer was analyzed with percentage. Comparison of IOP between rebound tonometer and applanation tonometry was presented.

Results: The rebound tonometry was well tolerated by all participants and caused no complaints, discomfort, or adverse events. Totally 42 myopic eyes of 42 subjects were included in the study. The average age of these participants was 10 years old, range from 5 to 16. Median = 10 years old. The average IOP of the right eye by rebound tonometer was 17.4 ± 3 mmHg, and 17.1 ± 3 mmHg by applanation tonometry. Nearly 19%, 33%, and 24% of difference of IOP readings between rebound tonometer and Tono-Pen applanation are within 0 mmHg, 1 mmHg, and 1-2 mmHg, respectively.

Conclusions: Rebound tonometry has good correlation with applanation tonometry and 76.1% of differences between two tonometers are <2 mmHg. The advantage of drop-free rebound tonometry has made it easier to obtain IOP readings in myopia children under atropine treatment.

Keywords: Atropine; intraocular pressure in children; myopia; rebound tonometry.

Figure 1

Schematic of ICARE tonometer display window for intraocular pressure and reliability. The most reliability reading is accompanied by a solid letter P. The next three levels of reliability are accompanied by the letter P and a horizontal line either at the bottom, the middle, or the top, displayed as solid, bottom, middle, and top, respectively

Figure 1 (a and b)

(a) Differences of intraocular pressure between two measurements by rebound tonometry and applanation tonometry (n = 42, two with unreliable applanation readings were excluded). (b) Percentage of difference of intraocular pressure between ICARE and tonopen

Figure 2

Reliability at first try of intraocular pressure measurement

Figure 3

The Bland–Altman plot of the average versus the difference of intraocular pressure measurements between rebound tonometry and applnation tonometry (in mmHg). **Some points with same values (same average and same difference of intraocular pressure). Three cases had intraocular pressure average of 19 mmHg and 0 mmHg differences, two cases of average 19 mmHg and 2 mmHg differences, 2 cases of average of 17 mmHg and 0 difference, two of average 20 mmHg and 4 mmHg difference, etc.

Figure 4

Distribution of intraocular pressure by two tonometry

Figure 5

Agreement between intraocular pressure by rebound tonometer versus tonopen applanation (recording in mmHg)