International Ophthalmology 16: 163-166, 1992. �9 1992 Kluwer Academic Publishers. Printed in the Netherlands.

Postural behaviour of intraocular pressure following trabeeuloplasty

Mohinder Singh 1 & Baljit Kaur Department of Ophthalmology, National University of Malaysia, Kuala Lumpur, Malaysia (1present address: Ministry of Health, Salmaniya Medical Centre, P. O. Box 12, Bahrain, Arabian Gulf)

Accepted 28 February 1992

Key words: intraocular posture, pressure, trabeculoplasty

Abstract

Postural behaviour of intraocular pressure (IOP) was studied in 29 glaucomatous eyes before and after argon laser trabeculoplasty (ALT) and compared with that of 60 normal eyes. Although argon laser trabeculoplasty was successful in lowering the IOP below 21 mm Hg, it produced little effect on the postural behaviour of the IOP. No significant change was observed in the amplitude of postural rise of IOP in ALT treated eyes.

Introduction

The influence of body position on the intraocular pressure (IOP) has been investigated by many workers. In normal individuals an increase of 1-2 mmHg in the IOP on changing from the sitting to the supine position has been reported [1-3]. Transient changes in visual fields [4], electroreti- nograms and visual evoked potentials [5] have also been demonstrated in gravity inversion.

The mechanism of elevated IOP in the supine position is most likely due to reduced outflow facil- ity [2] caused by raised episcleral venous pressure since altered body position does not seem to change the aqueous production [6]. Loss of homeo- stasis due to damage to the adrenergic receptors in the anterior segment of the eye has been recently suggested as another possible explanation [7].

An abnormal rise of the IOP on lying down has been found in patients of primary open angle glau- coma [3, 8], low tension glaucoma [9] and ocular hypertension [2]. Vascular disorders like diabetes mellitus [10] and systemic hypertension [11] are also associated with an anomalous postural re- sponse of the intraocular pressure. The postural

response of IOP is therefore an important consid- eration in the treatment of glaucoma.

Argon laser trabeculoplasty (ALT) has now be- come a popular therapy in the management of open angle glaucoma. Its long term efficacy and safety have been well investigated [12]. To our knowledge the effect of ALT on the postural response of the lOP has not been studied. We therefore decided to investigate it in a select group of glaucoma patients.

Patients and methods

The patients included in this study were selected from our open angle glaucoma population who had been treated by argon laser trabeculoplasty as a primary procedure.

Selection criterion

All eyes had primary open angle glaucoma diag- nosed on the basis of optic disc changes, visual field defects and untreated IOP above 21mm Hg. Angles were gonioscopically open.

164 M. Singh & B. Kaur

I CONTROL [] PRE-RLT I POST-RLT

Omm Hg 2mm Hg 3mm Hg 4mm Hg 6mm Hg 8mm Hg I@mm H~

Fig. 1. Histogram of postural rise of 10P in the control and

glaucoma population.

- All eyes were not receiving any antiglaucoma drugs.

- All eyes showed an abnormal postural response of IOP (above 2 mm Hg) prior to ALT proce- dure.

- All eyes had their IOP reduced below 21 mmHg by ALT alone and did not require any anti- glaucoma medication.

The postural response of IOP was measured one day before ALT and once again six months after the ALT procedure. Perkin's hand held applanation tonometer was used to measure the IOP. The IOP was measured first in the sitting position in each eye separately. The subject was then asked to lie down on the examination table. No pillows were given to support the head. After about five minutes in the supine position, the IOP was again measured in each eye. All measurements were done by the same observer (MS). An average of three readings was taken as the final value.

Trabeculoplasty procedure

About 100 laser burns of 50 microns spot size were evenly placed in the anterior one third of the trabe- culum over the entire circumference of the cham- ber angle. Time exposure was 0.1 sec and the pow-

er ranged between 800 and 1200 milliwatts so as to produce a light burn. Topical 0.1% betamethasone qid and oral Diamox 250 mg six hourly were given for two days.

The postural response of the lOP was also tested in 30 normal persons who were attending for early cataract or refractive errors. There was no positive family history of glaucoma in our controls. There was no evidence of any significant ocular inflamma- tion, cardiovascular or respiratory disease in the studied cases. Subjects with diabetes mellitus and high myopia were excluded. None of our cases were receiving any systemic medication.

R e s u l t s

A total of 29 glaucomatous eyes (16 patients) ful- filled the selection criterion and formed part of this study. Postural response of IOP was studied in 60 matched control eyes for comparison. The results are shown in Tables 1-2 and Fig. 1.

Both groups were closely matched for age and sex. One male and two female patients were one- eyed. Most of the subjects were in the age range of 51-70 years. There was no significant difference in the postural response of the lOP with age and sex (p > 0.05 chi square test). The mean lOP readings are shown in Table 2.

An average rise of 1.76 mmHg in the IOP in the horizontal position was observed in normal healthy individuals. All the 29 glaucomatous eyes showed an average postural rise of 4.8 mmHg prior to ALT.

Table 1. Table showing the age and sex distribution.

Age group Control Patients Total

(years) Male Female Male Female Male Female

41-50 1 2 1 1 2 3 51-60 4 7 3 3 7 10 61-70 6 4 4 3 10 7

71-80 4 2 0 1 4 3

Total cases 15 15 8 8 23 23 Total eyes 30 30 15 14 45 44

The mean postural rise of the lOP of 4.2mmHg was seen in the post-ALT group. It was observed that the postural rise of IOP after the ALT proce- dure was not greater than that noted before the treatment.

It can be seen that 54 eyes (90%) in the control group showed either no rise at all or only 1-2 mm Hg elevation of IOP with altered body position. Only 6 (10%) normal eyes registered a postural rise of 3-4mmHg. However, all glaucomatous eyes showed a postural rise of more than 2 mmHg be- fore ALT. Twentyseven (93.1%) glaucomatous eyes showed a rise of more than 2 mmHg in IOP with change of posture after ALT. Only 2 eyes (6.9%) showed a rise of 2mmHg following laser therapy. 93.1% glaucomatous eyes thus retained the abnormal postural rise of lOP after laser trabe- culoplasty. It is also evident from Fig. 1 that there was no significant change in the amplitude of postu- ral rise of IOP after ALT.

Discussion

Elevation of intraocular pressure with change of body position has been suggested as one of the factors which result in tissue damage in low tension as well as in primary open angle glaucoma [9]. It is therefore desirable that a safe level of intraocular pressure be maintained at all times.

The present study has shown that an exaggerated postural rise of IOP has persisted in the ALT treat- ed eyes. Although in these eyes ALT alone was

Table 2. Mean (standard error) intraocular pressure in mm Hg.

Right eye Left eye Mean

Control sitting 14.6 (0.22) 14.3 (0.18) 14.45 (0.2) lying 16.42 (0.34) 16.0 (0.24) 16.21 (0.27)

Pre-ALT sitting 30.6 (0.57) 29.8 (0.84) 30.2 (0.71) lying 35.6 (0.54) 34.4 (0.68) 35.0 (0.61)

Post-ALT sitting 19.2 (0.76) 18.8 (0.64) 19.0 (0.7) lying 23.4 (0.68) 23.0 (0.58) 23.3 (0.63)

Postural behaviour of lOP 165

effective in reducing the lOP below 21 mmHg, it produced little effect on the postural behaviour of the lOP. Smith and Trope [13] have demonstrated that non specific beta blocker levobunolol had no effect on relative IOP changes with altered body position in normal volunteers. Parsley et al. [14] also showed that abnormal postural response of IOP in chronic open angle glaucoma is both re- tained and unaffected after trabeculectomy. For the first time we have shown that laser trabecu- loplasty did not alter the amount of pressure eleva- tion due to change of posture. ALT does not seem to change the abnormal local homeostasis which is thought to be present in the glaucomatous eye [15].

This study has confirmed earlier reports that high rise of intraocular pressure on assuming the horizontal position can occur as a consequence of the abnormal postural response. As most of our glaucoma patients are old they conceivably spend a considerable time lying supine while sleeping or otherwise. The progression of glaucomatous ocular damage can possibly occur in such cases even though their IOP as conventionally recorded in the sitting posture remains within the satisfactory range. It can be argued that while treating patients with established open angle glaucoma, it is equally important to watch the postural behaviour of their IOP. We suggest that the postural response of lOP should also be studied while assessing any ther- apeutic regimen for the management of glaucoma.

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