SCHIOTZ AND APPLANATION TONOMETRY

Localization in Glaucomatous Visual Field Loss Vulnerable to Posture-Induced Intraocular Pressure Changes in Open-Angle Glaucoma

PURPOSE

To investigate localization in glaucomatous visual field defects that are vulnerable to posture-induced intraocular pressure (IOP) changes.

DESIGN

Prospective cross-sectional study.

METHODS

Ninety-three eyes of 93 newly diagnosed cases with normal tension glaucoma were examined. The IOP was measured in both the sitting and lateral decubitus positions with an Icare rebound tonometer. Visual field tests were performed with a Humphrey Field Analyzer with the Central 30-2 program using Swedish Interactive Threshold Algorithm standard strategies. The total deviation (TD) map values of 51 tested points were used for the analysis. A regression analysis was conducted to investigate relationships between TD in each point or cluster and posture-induced IOP changes. A linear mixed-effects model was used to identify factors associated with TD changes in each visual field cluster. Main outcome measures included the relationship between posture-induced IOP changes and localization of visual field defects.

RESULTS

There were 54 women and 39 men (mean age, 53.4 ± 12.5 years). The mean IOP per Icare rebound tonometer was 15.5 ± 3.2 mm Hg in the sitting position and 18.8 ± 3.1 mm Hg in the lateral decubitus position. The postural IOP difference was 3.3 ± 1.8 mm Hg (P < .001; range, -1.0 to 7.7 mm Hg). There was a significant negative correlation between TD and posture-induced IOP changes in 4 contiguous central points located just above the horizontal meridian. A linear mixed-effects model revealed a significant association between the difference in postural IOP change and decreased TD in the superior paracentral visual field according to multivariate analysis (P = .010).

CONCLUSIONS

Posture-induced IOP variations have been shown to be associated with glaucomatous superior paracentral visual field defects.

Relationship between sleep position and glaucoma progression

PURPOSE OF REVIEW

As humans spend a considerable portion of life in the horizontal position, it is vital to better understand the effect of sleep position on glaucoma.

RECENT FINDINGS

The mean positional increase from the supine position to the lateral decubitus position (LDP) in recent literature is less than 2 mmHg for each eye in its dependent position and less than 1 mmHg in the nondependent position. The right LDP is most commonly favored sleeping position. Some evidence suggests that the positional increases persist and so could lead to worse glaucomatous progression in the dependent eye. However, multiple studies failed to find a strong association. Ideally future research will identify risk factors for higher positional increases to identify patients who may benefit from a change in sleep position. To date, medications and argon laser trabeculoplasty have been ineffective in blunting the positional increase, although glaucoma surgery does reduce it. Raising the head of the bed has been linked with blunting the increase as well.

SUMMARY

Certain sleeping positions appear to be associated with higher intraocular pressure, although the association between sleep position and glaucoma progression is not as clear.

Comparison of Aqueous Outflow Facility Measurement by Pneumatonography and Digital Schiøtz Tonography

Purpose

It is not known if outflow facilities measured by pneumatonography and Schiøtz tonography are interchangeable. In this study we compared outflow facility measured by pneumatonography to outflow facility measured by digital Schiøtz tonography.

Methods

Fifty-six eyes from 28 healthy participants, ages 41 to 68 years, were included. Intraocular pressure (IOP) was measured in the sitting and supine positions with a pneumatonometer. With the subject in the supine position, IOP was recorded for 2 minutes by using a pneumatonometer with a 10-g weight and for 4 minutes by using a custom digital Schiøtz tonometer. Outflow facility was determined from the changes in pressure and intraocular volume and a standard assumed ocular rigidity coefficient for each instrument, respectively, and by using an ocular rigidity coefficient calculated by measuring pressure without and with a weight added to the pneumatonometer tip.

Results

The outflow facility was 0.29 ± 0.09 μL/min/mm Hg by Schiøtz tonography and 0.24 ± 0.08 μL/min/mm Hg by pneumatonography (P < 0.001) when using the standard assumed constant ocular rigidity coefficient. Mean calculated ocular rigidity coefficient was 0.028 ± 0.01 μL-1, and outflow facility determined by using this coefficient was 0.23 ± 0.08 μL/min/mm Hg by Schiøtz tonography and 0.21 ± 0.07 μL/min/mm Hg by pneumatonography (P = 0.003). Outflow facilities measured by the two devices were correlated when the ocular rigidity was assumed (r = 0.60, P < 0.001) or calculated (r = 0.70, P < 0.001).

Conclusions

Outflow facilities measured by pneumatonography were correlated with those measured by Schiøtz tonography, but Schiøtz tonography reported approximately 10% to 20% higher facilities when using the standard method. When ocular rigidity was determined for each eye, differences were smaller. Measurements from these devices cannot be compared directly.

The Effect of Laser Trabeculoplasty on Posture-Induced Intraocular Pressure Changes in Patients with Open Angle Glaucoma

Purpose

To investigate the effect of argon laser trabeculoplasty (ALT) on posture-induced intraocular pressure (IOP) changes in patients with open angle glaucoma (OAG).

Methods

Thirty eyes of 30 consecutive patients with OAG who underwent ALT were prospectively analyzed. The IOP was measured using Icare PRO in the sitting position, supine position, and dependent lateral decubitus position (DLDP) before ALT and at 1 week, 1 month, 2 months, and 3 months after ALT.

Results

Compared to the baseline values, the IOP in each position was significantly decreased after ALT (all P < 0.001). During follow-up, the mean percentage of IOP reduction was similar in the sitting and supine positions, but was significantly lower in DLDP than in the sitting or supine positions (all P < 0.05). In terms of postural IOP changes, the IOP in the supine position and DLDP was significantly higher than that in the sitting position at the same time points during the follow-up period (all P < 0.001). The difference between the IOP in the supine position and DLDP during follow-up was significant (all P < 0.001). The extent of IOP differences between any positions did not show significant changes during the follow-up period (all P > 0.05).

Conclusions

ALT appears to be effective in lowering the IOP in various body positions, but the degree of this effect was significantly lower in DLDP. In addition, ALT seemed to have limited effects on posture-induced IOP changes.

Effects of trabeculectomy on posture-induced intraocular pressure changes over time

INTRODUCTION

To determine whether trabeculectomy affects postural-induced changes in intraocular pressure (IOP), and whether it is maintained.

METHODS

Thirty-six eyes of 36 patients with open-angle glaucoma who were scheduled for their initial trabeculectomy with adjunctive mitomycin C were prospectively examined. The IOP was measured in the sitting and the lateral decubitus position with an ICare rebound tonometer before, and 1, 3, and 12 months after trabeculectomy.

RESULTS

Twenty-nine eyes of 29 patients completed this study. The mean baseline IOP measured with the ICare tonometer was 17.4 ± 4.9 mmHg in the sitting position and 21.3 ± 5.6 mmHg in the lateral decubitus position (p < 0.001). This postural IOP difference, +3.9 mmHg, was reduced to +1.3 ± 1.7 mmHg at 1 month and to +0.8 ± 1.5 mmHg at 3 months after the trabeculectomy (p < 0.001 and p = 0.004 respectively). This decrease in the degree of posture-dependent IOP change was maintained at +1.7 ± 2.2 mmHg at 1 year postoperatively (p < 0.001). In three cases, the postural IOP changes returned to the baseline level, and all three had a failed bleb.

CONCLUSIONS

Our results indicate that trabeculectomy not only reduces the IOP but also reduces the degree of posture-induced changes in the IOP. Our findings also speculate that measuring the postural IOP changes after trabeculectomy might provide a clue on the functioning of a filtering bleb.

Blood flow in the optic nerve head and factors that may influence it

In the recent past there has been great interest in the blood supply of the optic nerve head (ONH), how to evaluate ONH blood flow, and what factors influence it, in health and disease. This is because evidence has progressively accumulated that there is vascular insufficiency in the ONH in both anterior ischemic optic neuropathy (AION) and glaucomatous optic neuropathy (GON)-two major causes of blindness or of seriously impaired vision in man. For the management and prevention of visual loss in these two disorders, a proper understanding of the factors that influence the blood flow in the ONH is essential. The objective of this paper is, therefore, to review and discuss all these factors. The various factors that influence the vascular resistance, mean blood pressure and intraocular pressure are discussed, to create a better basic understanding of the ONH blood flow, which may help us toward a logical strategy for prevention and management of ischemic disorders of the ONH.

The effect of posture on intraocular pressure and pulsatile ocular blood flow in normal and glaucomatous eyes

While an increase in the intraocular pressure on assumption of the supine position from the seated or upright position has been known for decades, the recent introduction of a means to quantify the pulsatile ocular blood flow has led to studies indicating a postural decrease in the pulsatile ocular blood flow. The factors contributing to the postural response of the intraocular pressure are reviewed, and those proposed for the postural response of the pulsatile ocular blood flow are discussed.

Intraocular pressure measurement after pars plana vitrectomy

The ability of various tonometers to measure intraocular pressure (IOP) accurately after pars plana vitrectomy was determined by using Schiøtz, Goldmann, and Digilab pneumatic tonometers before and after the procedure in 47 eyes. Seventeen of these eyes underwent intraoperative fluid-gas exchange and had an intravitreal gas bubble on the first postoperative day. The Schiøtz tonometer underestimated the Goldmann IOP by more than 10 mmHg in 6 (35%) of 17 eyes after vitrectomy with intravitreal gas and 4 (13%) of 30 eyes without intravitreal gas. The Digilab tonometer did not underestimate the Goldmann IOP by more than 10 mmHg in any eye postoperatively. However, the Digilab tonometer underestimated the Goldmann IOP by more than 5 mmHg in 3 (18%) of 17 eyes after vitrectomy with intravitreal gas and two (7%) of 30 eyes without intravitreal gas.

The vascular basis of the positional influence of the intraocular pressure

By measuring intraocular pressure in different body positions from 60 degrees semiupright to 30 degrees head down, a nonlinear relationship between IOP increase and body position was confirmed. IOP postural response in individual subjects was roughly correlated to ophthalmic arterial pressure and to the episcleral venous pressure postural response. In one series of subjects, the episcleral venous pressure increments due to posture wa; parallel to the applanation-indentation disparity in the same individual eyes. Differential tonometry with applanation or indentation procedures under blind conditions gave significantly low indentation readings. It is concluded that IOP postural response depends on arterial and venous vascular changes when subjects move from an erect to a horizontal body position. Blood expulsion from the choroid by indentation tonometry might be the reason that this tonometric procedure does not measure IOP changes based on vascular changes.

Rapid pneumatic and Mackey-Marg applanation tonometry to evaluate the postural effect on intraocular pressure

A postural study was conducted in three separate groups of subjects. The first group comprised 20 women volunteers with an average age of 20-75 years. In this group, the study was conducted by the pneumatonograph only. Mean pressure recorded was 15-65 +/- 0-25 mmHg and there was an average rise of 1-4 mmHg in supine posture. Groups 2 and 3 comprised 151 non-glaucomatous and 108 glaucomatous eyes respectively in the age range of 30 to 85 years. In these two groups, the study was conducted using the PTG and the Mackay-Marg tonometer. Clinical evaluation of the Mackay-Marg with the PTG gave significant correlation, with mean Mackay-Marg readings being 1-13 mmHg higher. The intraocular pressure when changing from seated to the supine position increased on average by 2-71 and 4-04 mmHg, respectively in Groups 2 and 3 and by 2-51 and 3-72 mmHg by Vackay-Marg, suggesting a higher change in glaucomatous subjects. Pressure on resumption of sitting was found to be lower than the initial pressure. Postural change also showed some direct relationship with age in non-glaucomatous subjects.

[Comparative intraocular pressure measurements with position independent hand-applanatation tonometers (author's transl)]

A study of comparative intraocular pressure measurements was made using the hand-held applanation tonometers of Perkins and Draeger in the sitting and lying patient. A series of 100 patients was investigated by two observers taking the pressures with both tonometers under blind conditions. The statistical evaluation of the data revealed an average pressure increment when lying down of 2.5 to 3 mm Hg for both observers and both tonometers. This postural response is fully reversible when getting up and an overshoot-phenomenon statistically significant is noted. The pressure increment when lying down is not related to initial pressure level and there is no clear relationship to the age of the patients tested. Interobserver variation as well as variations of both tonometers are evaluated. The effect of repeated tonometry in this study is considered. Some aspects of position influence on the intraocular pressure are discussed.

A clinical evaluation of the applanation pneumatonograph

The applanation pneumatonograph combines pneumatic and electronic systems. It is used for measuring intraocular pressure, aqueous humour dynamics, and ocular pulsation. In the present study the PTG and the Goldmann tonometer have been used to measure the intraocular pressure in 40 normal and 40 glaucomatous eyes. It has been found that the results of the two instruments correlate well. The PTG readings have, generally, been found to be higher with a mean difference of 0-75 mmHg in the normal and 1-25 mmHg in the glaucomatous eye. The mean ocular pulse as determined in normal eyes was 3-25 +/-0-21 mmHg.

Comparative intraocular pressure measurements with the pneumatonograph and Goldmann tonometer

Comparative intraocular pressure measurements made with the pneumatonograph and the Goldmann tonometer showed close agreement with a statistically higher mean pressure when using the pneumatonograph. Significant changes in mean pressure differences between the two instruments were seen upon changing the pneumatonograph calibration and with change in the order of testing (which instrument was used initially). However, transient biologic changes in an individual eye producing minute-to-minute fluctuations in intraocular pressure may be equal to or larger than differences in measurement between instruments.