Difference in Intraocular Pressure between Sitting Versus Supine Positions in Healthy and Glaucomatous Children by Rebound tonometery

 INTRODUCTION

Glaucoma can occur alone or in conjunction with other ocular or systemic illnesses that affect both adults and children. ¹ The measurement of intraocular pressure (IOP) is an important aspect of a standard eye checkup, especially for glaucoma patients. Indeed, in many circumstances, the major risk factor that physicians can change is increased IOP. ²

Because it is often difficult to evaluate visual fields with minor changes in optic disc morphologic features that occur in young children, the importance of the patient's IOP was to aid in diagnosis, estimate the prognosis of glaucoma, and determine the efficiency of glaucoma treatment.³

IOP is dynamic and can be influenced by a variety of factors, one of the most important of which has been proven in earlier studies: variations in body position. ⁴

Furthermore, some investigations have shown that the difference between IOP values obtained in the supine and seated positions in adults varies greatly. In research comparing healthy people and glaucoma patients, the discrepancy ranges from 0.3 to 5.6 millimetres of mercury. ⁵ In adults, intraocular pressure (IOP) is commonly measured in a sitting position, but in pediatric age group, it is commonly measured in a supine position under general anesthesia .⁶ Although, there are many studies that already studied the effect of general anesthesia on the intraocular pressure (IOP), but there is no clear information or confirmed study to clarify the effect of supine position only on the intraocular pressure (IOP) among pediatric age group. Nowadays, it has become possible to measure IOP in a sitting and supine positions among pediatric age group without general anesthesia, but there is no clear information if there is a change in the intraocular pressure between the sitting versus supine positions in young patients.⁷

GAT devices are available in the form of handheld battery-powered tonometers (e.g., Perkins) that may be utilised with a patient in a supine position. However, they have the disadvantage of requiring anaesthesia, fluorescein staining, and contact with the cornea.

* Noncontact air-puff tonometry works on the same premise as GAT, except it flattens the cornea using a puff of air. Noncontact airpuff tonometry is less reliable with higher IOP measurements, despite the fact that it does not require topical anaesthetic. ⁸

The Tono-Pen is a portable tonometer that combines the qualities of applanation and indentation tonometry. It does, however, require topical anaesthetic and the tip of the instrument is cumbersome for a youngster.¹

In the measurement of IOP in young children, the iCare tonometer appears to be the most useful tool. ⁹ According to the American Academy of Ophthalmology's recent Ophthalmic Technology Assessment, rebound tonometry was a reasonably accurate instrument that avoided the requirement for general anaesthesia in many children. , also, it can measure IOP in both supine and sitting position.¹⁰

The aim of this work was to study the effect of body posture (supine position versus sitting position) on the intraocular pressure (IOP) measurements in normal healthy children and glaucomatous children by using a Rebound tonometry.

PATIENTS AND METHODS

This is a cross-sectional observational clinical study that was carried out on 80 children, divided into 20 cases of children with glaucoma, and 60 children with normal healthy eyes as control, all children attending the outpatient pediatric ophthalmology clinic of (Kids eye center of memorial institute of ophthalmic research), between December 2020 and August 2021.

Inclusion criteria: Children of both genders, children of age between (4-12) years, normal anterior segment, and glaucomatous or suspected glaucomatous child.

Exclusion criteria: Contact lens wearer, children with history of corneal abnormality, children with history of ocular trauma or ocular surgery other than glaucoma surgery, children with history of ocular inflammation or retinal detachment, children with history of any physical, or mental problem, children using steroid as topical or systemic medications, and uncooperative child.

Informed consent: All children’s guardians were informed about the nature of the study and the details of the procedure and asked to provide written consent.

All children were subjected to the following:

Complete history taking include: Personal history as name, age, gender, and race. Ocular history: as previous history of trauma, and other ocular surgeries, onset, course, and duration of glaucoma. Medical history of current and previous medications the patient had been taken including systemic and topical steroids, anti-glaucoma medications, and  past history.

Examination (Pre-test evaluation): General examination: to exclude any systemic conditions that are usually associated with rising of IOP as, hypertension, obesity, and  ocular examination all studied subjects were examined using Hand held Slit Lamp examination or binocular indirect Ophthalmoscope to exclude any abnormality or ocular surface disease that may lead to change in IOP.

Several studies showed that IOP in normal healthy children ranged from 10 to 28 mm Hg, with Mean IOP 17.6 ±  2.7 mm Hg.^{1, 11, 12}  So, in our study, 35 healthy subjects by examination who presented with a mean IOP over 21mmHg in at least one eye were referred to the pediatric glaucoma clinic for further assessment, from those 35 subjects,  22 subjects were confirmed that no pathology or abnormalities were present so data from these subjects were included in the normal group ,13 subjects diagnosed as glaucoma and scheduled for medical , surgical or both and included in the glaucoma group .

Test protocols:

All children were not allowed to drink any liquids immediately an hour before the first measurement. During measurements, To prevent acts that may raise pressure on the eyelids or globe, youngsters were urged to relax (e.g. lid squeeze). A single experienced researcher took IOP measurements with an Icare PRO rebound tonometer (Icare; Tiolat Oy, Helsinki, Finland), which can be used in both the sitting and supine positions. . When the children arrived at the outpatient clinic for assessment, IOP measurements were taken between 9:00 and 11:30 a.m.

All children were seated for 10 minutes, The children were then instructed to look straight ahead to a distant point while the examiner brought the tonometer close to their eyes. After the tonometer was appropriately positioned, six serial IOP measurements were collected from their eyes in rapid succession while they remained in a sitting position. The patients were placed in a supine position on the clinic stretcher for the following 10 minutes, with no pillow. before having their IOP measured again. A new probe was used for each child.

Icare PRO tonometer has an automatic system The highest and lowest measurements are removed, and the remaining four readings are averaged. The reliability indicator, which reflects the standard deviation of individual IOP measurements, is next calculated. According to the color-coded measurement reliability technique of the Icare PRO tonometer, green signifies the lowest variability and best reliability, yellow indicates moderate fluctuation and dependability, and red indicates high variability and low reliability. For statistical analysis, only green average values were used. , indicating low variability and good reliability.

Statistical analysis:

The data was processed using the SPSS software programme for Windows version 23.0 (Chicago, IL, USA). For categorical data, the children's characteristics were tallied using number and percent, and for continuous variables, mean, range, and standard deviation (SD). The chi-square test was used to compare mean values of continuous variables and the Student t test was used to examine categorical variable distributions. The paired t test was used to complete comparisons between groups for continuous variables. A 0.05 p-value was utilised in all statistical tests.

RESULTS

Table 1: Comparison between cases and control groups as regard children age and gender.

The study was carried out on 80 children (their age ranged from 4-12 years), divided into 20 cases of children with glaucoma, and 60 children with normal healthy eyes as control. The age of glaucomatous children ranged from 6-12 years with a mean of 9.35 ± 1.69 years, with no significant difference between case and control groups (P = 0.091). As regard gender, the majority of glaucomatous children, 11 (55%) were females and 9 (45%) were males, with no significant difference between case and control groups (P = 0.553) (Table 1).

Table 2: Change in IOP among case and control group during sitting and supine positions.

With reference to IOP measurement among case group (glaucomatous patients) , there was significant increase in IOP measurement on supine position when compared with values obtained in sitting position in right eye as well as left eye (P1 = 0.001, 0.002 respectively). Moreover, there was no significant difference between right and left eyes in both positions (P2 = 0.809, 0.873 respectively). The mean difference in IOP measurement between supine and sitting positions was 4.86 mmHg in right eye, and 4.78 in left eye. With reference to IOP measurement among control group (healthy children), there was significant increase in IOP measurement on supine position when compared with values obtained in sitting position in right eye as well as left eye  (P1 = 0.007, 0.008 respectively). Moreover, there was no significant difference between right and left eyes in both positions (P2 = 0.898, 0.911 respectively). The mean difference in IOP measurement between supine and sitting positions was 3.49 mmHg in right eye, and 3.58 in left eye (Table 2).

Table 3: Correlation between IOP and age of glaucomatous children.

There was no significant correlation between IOP measurement and age of glaucomatous children (P = 0.551, 0.294), as shown in (Table 3).

Table 4: Relation between IOP and gender of glaucomatous children.

With reference to IOP measurement among glaucomatous children, there was no significant relation between gender and IOP measurement on sitting or supine position (P = 0.145). The mean difference in IOP measurement between supine and sitting positions was 5.22 mmHg in male patients, and 4.49 in female patients, as shown in (Table 4).

Table 5: Relation between IOP and glaucoma treatment of glaucomatous children.

With reference to IOP measurement among glaucomatous children, there was no significant relation between glaucoma treatment modalities and IOP measurement on sitting or supine position (P = 0.167). The mean difference in IOP measurement between supine and sitting positions was 4.30 mmHg in patients received medical treatment, 4.80 mmHg in patients scheduled for medical treatment, 5.18 mmHg in patients underwent surgery, 4.94 mmHg in patients scheduled for surgery, 3.95 mmHg in patients received medical treatment and scheduled for surgery, and 5.43 mmHg in patients scheduled for surgery plus medical treatment as shown in (Table 5).

Table 6: Comparison between cases and control groups as regard change in IOP during sitting and supine positions.

There was highly significant increase in IOP among glaucomatous children than healthy control (P1 = 0.001), as well, there was highly significant increase in IOP during supine position than sitting position in both groups (P2 = 0.001). The mean difference in IOP measurement between supine and sitting positions was 5.03 mmHg in glaucomatous children, and 3.27 in healthy control, as shown in (Table 6).