Efficacy of Using the Icare´┐Ż Rebound Tonometer Combined with a Simple Supplementary Device for the Self-Examination of Intraocular Pressure

Research Article

Austin J Clin Ophthalmol. 2014;1(4): 1021.

Efficacy of Using the Icare® Rebound Tonometer Combined with a Simple Supplementary Device for the Self-Examination of Intraocular Pressure

Ayako Iwama, Kazuhiko Mori*, Shigeta Naruse, Yoko Ikeda and Shigeru Kinoshita

Department of Ophthalmology, Kyoto Prefectural University of Medicine, Japan

*Corresponding author: Kazuhiko Mori, Department of Ophthalmology, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Hirokoji-agaru, Kawaramachidori, Kamigyo-ku, Kyoto 602-0841, Japan

Received: April 10, 2014; Accepted: May 10, 2014; Published: May 13, 2014

Abstract

Purpose : To evaluate the efficacy of using the Icare® (Icare Finland Oy, Vantaa, Finland) rebound tonometer combined with a simple supplementary device for self–measurement of intraocular pressure (IOP).

Subjects and Methods : This study involved 104 eyes of 52, healthy righthanded volunteers. IOP was consecutively measured using the Icare® by an ophthalmologist and by the participants themselves through self–examination. To accurately position the Icare® probe against the center of the cornea during self–examination, a colored board with a 7–mm–diameter central hole affixed to an eyeglass frame was used. Participants were then instructed to wear the frame, insert the Icare® probe into the hole, and self–measure the IOP of both eyes.

Results : Correlation was found between the IOP readings obtained by the ophthalmologist and those obtained by self–examination. The correlation was stronger when the position between the probe and cornea was in better alignment. In 42 eyes, the probe was precisely directed at the center of the cornea, and those readings were found to be strongly correlated.

Conclusions : The Icare® combined with a simple supplementary device proved effective for producing reliable IOP readings, thus providing the possibility of using the Icare® for self–examination of IOP in both the home and clinical settings.

Keywords : Intraocular pressure; Rebound tonometer; Self examination

Introduction

It is well known that glaucoma is a leading cause of permanent blindness worldwide [1]. Although Intraocular Pressure (IOP) is no longer considered to be a cause of glaucoma, it is still an important risk factor for its development [2,3]. In addition, IOP measurement is an important indicator by which to evaluate the efficacy of various treatment methods [4]. Therefore, tonometry is still considered to be one of the gold–standard procedures associated with the treatment of glaucoma in the clinical setting. Despite the availability of numerous portable devices, the majority of ophthalmologists rely solely on Goldmann Applanation Tonometry (GAT) as the standard method for measuring IOP, a method in which the obtained IOP readings are used to guide decisions regarding patient management [6]. However, it has been reported that IOP can vary throughout the day and that IOP diurnal fluctuation could influence the diagnostic and prognostic evaluation of the glaucomatous disease [6]. Therefore, a portable and easy–to–use tonometer would be extremely valuable in the clinical setting, especially for the detection of diurnal changes in IOP, as well as for self–examination of IOP in the home [7,8].

Originally released in 2005, the Icare® (Icare Finland Oy, Vantaa, Finland) is a hand–held rebound tonometer that has a solenoid mechanism which launches a magnetized probe and detects its motion parameters during impact on the cornea [9,10]. This tonometer is light and compact, and can measure IOP without the need for topical anesthesia. Thus, the characteristics of this tonometer may prove to be ideal for the self–examination of IOP in the home setting. Rebound tonometry is based on a moving object impacting with the ocular surface while monitoring the motion parameters of that object [9,10]. When IOP is low, the deceleration of the probe is less than that observed when IOP is high. Consequently, the higher the IOP, the shorter the duration of the impact. IOP is calculated from the measurement of impact duration and maximum deceleration [9]. In order to obtain more accurate IOP readings with the Icare® (i.e., no error bars), extra care must be taken to ensure that the probe is held perpendicular to the center of the cornea and that the measurements are taken as quickly as possible, with minimal movement of the operator’s hand or the patient’s eye [11]. In addition, it is vital that the operator stand directly in front of the patient in order to ensure that the probe is not tilted off–axis in either the horizontal or vertical plane. Thus, this difficulty is one that needs to be resolved in order for the Icare® to be effectively and easily used as a home tonometer for the self–examination of IOP.

We previously examined whether there was any correlation between the Icare® tonometer IOP value when measured by an ophthalmologist and by the patients themselves through selfexamination. However, no strong correlation was found between the values measured by each method due to the difficulty that the patients experienced in accurately positioning the Icare® probe at the center of the cornea during self–examination (data not published).

In this present study, we evaluated the efficacy of using the Icare® tonometer combined with a simple supplementary device for the selfexamination of IOP. The latest Icare® model available for use in Japan was released in 2012, and it provides some advantages compared to the previous Icare® model. In specific, it offers the ability to check the IOP of patients while their spine is in a reclining position. The Icare® used in this present study has some merits compared to the latest type; i.e., it is lighter in weight, more easily to handle for selfexamination, and it is lower in price. Soon, a newer Icare® model that is specifically designed for self–examination will become available in Japan, however, the Icare® model used in this present study is stilluseful for the self examination of IOP by using a supplementary method.

Participants and Methods

In this present study, a total of 104 eyes of 52, healthy righthanded volunteers (45 males and 7 females; age range: 25–51 years, mean age: 36.0±7.7 years) were enrolled. Participants who regularly used soft contact lenses were instructed to not wear the lenses for at least 24 hours prior to participation in the study. All participants had no history of ocular surgery, were free of ocular symptoms, and were not taking any medication. Informed consent was obtained from all subjects after receiving a detailed explanation of the study protocol.

IOP was consecutively measured using the Icare® tonometer by an ophthalmologist (A.I.) and by the participants themselves. Prior to the examination, the participants were instructed in the proper use of the Icare®. In order to accurately position the Icare® probe against the center of the cornea during self–measurement, a single eyeglass frame which has a capability of changing the pupillary distance up to 56–70 mm was used. We adjust the glass in relation to the pupil distance for each patient prior to IOP measurement. A colored board with a 7–mm–diameter hole in its center was affixed to the eyeglass frame in place of the usual lens (Figure 1A). The participants were then instructed to wear the frame, insert the Icare® probe into the hole, and self–measure the IOP of both eyes with their most convenient method (Figure 1B). Patients always check their probe position by use of a mirror in order to insure that the measurements are taken correctly with the Icare. The accuracy of the self–measurements by the participants was categorized into four subgroups based upon whether the position of the hole was in alignment with the papillary center and whether the position of the probe–tip was in alignment with thecenter of the cornea (Figure 2). Consecutive measurements were then obtained from each eye until either a mean reading displaying a static P with no bar (P) was acquired, or a total of 6 readings were performed, regardless of standard deviation (SD). The total number of attempts needed to achieve a P reading was then recorded for each participant.