Diurnal Intra ocular Pressure

Correlation to Automated Perimetry JESS SMITH, MD

Abstract: Patients referred to a centralized glaucoma laboratory obtained intraocular pressure measurements every two hours from 5:00 am to 3:00 pm. Analysis revealed 400 eyes with visual field defects and 400 eyes without visual field defects as determined by Octopus perimetry of the central 20°. The diurnal variation in intraocular pressure was 6.2 mmHg ±3.6 for those with visual field defects and 5.5 mmHg ±2. 7 for those without visual field defects. There was no statistical significance in the mean diurnal variation between the two groups (P = 0.91 ). The highest intraocular pressure tended to occur at either 5:00 am to 7:00 am or 11:00 am to 1:00 pm in both groups. The lowest intraocular pressure tended to occur between 7:00 am to 9:00 am or 1 :00 pm to 3:00 pm in both groups. No significant differences were noted in the distribution between the two groups with regard to the time of the highest or lowest intraocular pressure. In the group with visual field defects, 30% had an intraocular pressure of <23 mmHg and 23% had an intraocular pressure of ;::::23 mmHg at all five time periods. [Key words: automated perimetry, diurnal variation in intraocular pressure, glaucoma, Goldmann tonometer, intraocular pressure, Octopus perimeter.] Ophthalmology 92:858-861, 1985

Diurnal variations in intraocular pressure (lOP) have been studied by many authors in normal individuals as well as in patients in whom the diagnosis of glaucoma was established on clinical examination with or without visual field defects utilizing the Goldmann perimeter. 1

-5

Within the last several years, the development of sophisticated static automated perimeters has made it possible to evaluate the visual field in a standardized and reproductible manner and to store the data in the computer from retrieval and analysis.6.7

The lOP measurement and the visual field assessment are important factors in the diagnosis and management of glaucoma. 8 Therefore, the possible correlations be­tween these two aspects of testing are of clinical signifi­cance.

This is a report of the computer analysis of the correlations between automated perimetric data and a modified diurnal lOP curve.

From the Cullen Eye Institute, Baylor College of Medicine, Houston.

Presented at the Eighty-ninth Annual Meeting of the American Academy of Ophthalmology, Atlanta, Georgia, November 11-15, 1984.

Reprint requests to Jess Smith, MD, Cullen Eye Institute, Baylor College of Medicine, 6501 Fannin, Houston, TX 77030.

858

MATERIALS AND METHODS

A centralized glaucoma service laboratory was estab­lished in order to obtain intensive clinical evaluation on patients referred for study. Standardized testing included systemic and ocular history, Goldmann applanation tonometry, Octopus perimetry, Goldmann perimetry, stereophotographs of the optic nerves, blood chemistry analysis, and blood pressure measurements. The data from this intensive evaluation was stored in the computer for retrieval and analysis.

In the present study, only the data obtained from Octopus automated perimetry and Goldmann applana­tion tonometry was analyzed.

Goldmann applanation tonometry was performed every two hours from 5:00am to 3:00pm by ophthalmic technicians. This data was immediately entered by the technician into a computer terminal located adjacent to the tonometer.

Following the 3:00 pm measurement of the lOP, the eyes were dilated for optic nerve stereophotography. The intraocular pressures were measured after the photog­raphy; however, these were not included in this report in order to avoid any possible effects of the pharmacologic agents.

SMITH • DIURNAL PRESSURE

Table 1. Criteria for Visual Field Defects in Central 20°, Octopus Program #31

Criteria Description

1. Two contiguous points, 5 dB or more below age adjusted normal, in an area not adjacent to the blind spot.

2.

3.

One point, 10 dB or more below age adjusted normal, in an area not adjacent to the blind spot.

Three points 5 dB or more below age adjusted normal, in an area adjacent to the blind spot.

The visual field analysis utilized the automated Oc-. h b · I r rted 6'9' 10 topus penmeter as as een prev10us y epo .

Program no. 31 evaluated the central 30° with test locations at intervals of 6 degrees. Although the central 30° was tested, only the data from the central 20° was included in this report in order to eliminate the rim edge artifacts created by high refractive errors or the lens holder.

The characteristics of glaucomatous visual field defects on the Octopus perimeter have been the subject of several investigations. 11

-13 The criteria for visual field

defects utilized in this report are listed in Table 1 and are similar to previous reports to the American Academy

0 U ' s . t 7 14 15 and to the ctopus sers oc1e y. ' ' The patients involved in this study were referred for

testing by 22 ophthalmologists who examined the patients and made the tentative diagnosis of glaucoma damage, glaucoma suspect, or ocular hypertension. Thus, as many ophthalmologists were involved in the referral process, many individual criteria for referral were un­doubtedly utilized. In some cases, the referring ophthal­mologist may have been treating the patient with anti­glaucomatous therapy. However, in ord~r to avo~d ~he effects of pharmacologic agents on the dmrnal vanat10n in lOP, the patients were instructed to discontinue all topical and systemic anti-glaucomatous therapy for at least two days prior to the visit to the laboratory.

For the purpose of this report, the computer identified 400 eyes with a diurnal lOP profile which met the criteria for having visual field defects and an additional 400 eyes with a diurnal intraocular pressure profile without visual field defects.

RESULTS

The range of the lOP taken at the five time periods on 400 eyes with visual field defects and 400 eyes

Table 2. Range of Intraocular Pressure

With visual field defects (400 eyes: 5 measure-

Range Mean Standard Deviation

ments per eye) 8 to 57 mmHg 22.1 mmHg ±7.4 Without visual field defects

( 400 eyes: 5 measure-ments per eye) 8 to 50 mmHg 21.0 mmHg ±5.4

Table 3. Diurnal Variation in Intraocular Pressure (lOP)

With visual field defects

Variation in lOP

Mean~

lOP

(400 eyes) 1 to 20 mmHg 6.2 mmHg Without visual field defects

(400 eyes) 1 to 19 mmHg 5.5 mmHg

Standard Deviation

±3.6

±2.7

without visual field defects is shown in Table 2. The mean intraocular pressure for those eyes with visual field defects was 22.1 mmHg ±7.4, and 21.0 mmHg ±5.4 for those without visual field defects. No statistically significant difference was found between the mean intra­ocular pressure of the two groups using the two-tailed t­test (P = 0.41 ).

The diurnal variation in lOP is shown in Table 3. For those eyes having visual field defects, the diurnal lOP varied from 1 to 20 mmHg with a mean variation of 6.2 mmHg ±3.6. For those eyes without visual field defects, the diurnal variation in lOP was 1 to 19 mmHg with a mean variation of 5.5 mmHg ±2.7. No statistical significant difference was found between the mean diur­nal variation in lOP between those eyes with visual field defects and those without visual field defects using the two-tailed t-test (P = 0.91 ).

Figure 1 is a graph of the number of eyes which ?ad their highest peak lOP recorded at each of the tlme periods listed. In the group with visual field defects, 114 had their highest lOP at 5:00 am to 7:00 am, and 136 had their highest lOP at 11:00 am to 1:00 pm. In the group without visual field defects, 148 had their highest lOP between 5:00 am and 7:00 am, and 100 had their highest lOP between 11 :00 am and 1 :00 pm. As the intraocular pressure appeared to peak at the same two time periods in both groups, no significant difference was noted in the distribution between the two groups with regard to the time of the highest lOP (chi-square = 14.16with4df).

Figure 2 is the time of measurement at ~hich_ the lowest lOP was recorded in those 400 eyes w1th v1sual field defects and those 400 eyes without visual field defects. In those eyes with visual field defects, 128 had their lowest lOP at 7:00 am to 9:00 am, and 108 had their lowest lOP at 1:00 pm to 3:00 pm. For the group without visual field defects, 128 had their lowest lOP at 7:00 am to 9:00 am and 120 had their lowest lOP at 9:00 am to 11 :00 am. As the lowest lOP appeared to occur at the same two time periods in both groups, no significant difference was found in the distribution of the lowest (chi-square = 3.83 with 4df).

An lOP of 23 mmHg or greater has been utilized in the past as a referral for glaucoma evaluation in screening programs. 16

•17 Analysis of those eyes with visual field defects showed that 30% had an lOP of less than 23 mmHg at every one of the time periods. Analysis also showed that 23% of the eyes had an lOP equal to 23 mmHg or greater at every one of the five time periods. Thus, 47% of the eyes with visual field defects had an

859

OPHTHALMOLOGY • JULY 1985 • VOLUME 92 • NUMBER 7

175 --With visual field defects

150 ---- Without visual field defects Ul ... > 125 ... ... 100 0

a: 75 ... Ill :IE 50 :I z

25

0~----~----~----~----~------~--~ 5:00 a.m. 7:00 a.m. 9:00 a.m. 11:00 a.m. 1:00 p.m.

to to to to to 7:00 a.m. 9:00 a.m. 11:00 a.m. 1:00 p.m. 3:00 p.m.

Fig 1. The number of eyes are plotted against the time of the highest (peak) intraocular pressure.

lOP of less than 23 mmHg on at least one of the five time periods tested.

DISCUSSION

Glaucoma is a disease associated with an elevated lOP, damage to the optic nerve, and visual field loss. 18

The level of the intraocular pressure is, therefore, basic to the diagnosis of glaucoma. However, a single mea­surement of the lOP in the ophthalmologist's office may fail to demonstrate an elevated lOP due to the large variation in pressure which occurs during the 24-hour day. A diurnal lOP profile would be expected to dem­onstrate both the peak pressure and any elevation in pressure. In addition, a diurnal lOP profile might be very useful clinical information for the individual patient to provide a baseline for future care and to serve as a guideline to the patients therapeutic response to various medications and procedures. 8

However, a true diurnal intraocular pressure profile for an entire 24-hour period is difficult to perform as it usually requires admission to a hospital, involves con­siderable technician support, and incurs considerable expense to the patient. A modified lOP profile, on the other hand, can be performed rather easily and inexpen­sively if it is performed as part of other glaucoma testing procedures in a centralized center. In this study, the lOP measurements were performed every two hours from 5:00 am until 3:00 pm. These time periods were selected in order to incorporate the times previously reported during which the majority of patients with or without glaucoma will have their highest 10Ps.2

•4

•19

-21

Analysis of the highest lOP measurement in both those eyes with and those without visual field defects showed that over 60% had the highest lOP recorded between 5:00 am and 7:00 am or between 11:00 am and 1:00 pm. Thus, peaks in lOP tended to occur at a time either before the opening of most private practice offices or at a time which spans the usual lunch period. Therefore, a single measurement in the usual office setting may well miss the peak lOP on many individuals.

The mean diurnal variation in lOP in previous reports in patients with glaucoma was considerably higher than

860

175r-------------------------------------,

150 Ul ... > 125 ... ~ 100

::; 75 Ill

~ 50 z

25

--With visual field defects

---- Without visual field defects

0~----~----~----~----~------~----~ 5:00 a.m. 7:00 a.m. 9:00 a.m. 11:00 a.m. 1:00 p.m.

~ ~ ~ ~ ~

7:00 a.m. 9:00 a.m. 11 :00 a.m. 1 :00 p.m. 3:00 p.m.

Fig 2. The number of eyes are plotted against the time of the lowest (trough) intraocular pressure.

found in our group with visual field loss.20-

23 These differences can possibly be explained by the methodology of this study as, (I) visual field defects in this report were defined as abnormalities on an automated peri­metric examination and this may not be analogous to defects with other perimeters, (2) all of the study patients in this report were referred by ophthalmologists specifi­cally for glaucoma testing and thus, may differ from other patient populations, (3) many of the other reports defined patients as having glaucoma only if they had previously demonstrated an elevated lOP and thus, the selection process was different from that used in this report.

Many glaucoma screening programs have utilized lOP of 23 mmHg for a referral basis as this level is three standard deviations from the presumed mean lOP of 15.5 mmHg ±2.5.8 In order to evaluate the validity of the concept of referral based only on tonometry, analysis was performed on all lOPs of 23 mmHg or greater in those eyes which had visual field defects. Only 23% of the eyes with visual field defects had lOP equal to 23 mmHg or greater at all five time periods and would have been referred regardless of the time they had been screened. However, 47% had lOP of less than 23 mmHg on at least one of the five time periods; thus, it is theoretically possible that all of these might have been missed in a screening study as there was at least one time period at which the lOP would have been less than required for referral. Of even more significance, 30% of the eyes with visual field defects had lOP of less than 23 mmHg at every one of the five time periods and therefore, none of these would have been referred for further evaluation. As 30% of the group with visual field defects did not have "elevated intraocular pressure," they might be clinically diagnosed as having "low tension glaucoma" and thus, this report is consistent with other reports in the literature showing that "low tension glaucoma" may account for even as much as 50% of patients with visual field defects in selected populations. 22

The implication of the fact that many of the patients with visual field defects would not have been referred if the referral were based on single or even multiple lOP measurements is that the method of screening for glau­coma by tonometry is of limited value. The value of

SMITH • DIURNAL PRESSURE

tonometry was previously questioned when the report of the glaucoma cooperative study showed that the number of cases of glaucoma missed by tonometric screening was approximately 50%.23 Additional methods of glaucoma screening available for the community as well as for the office practice of ophthalmology include automated perimetry, ophthalmoscopy, and photography of the optic nerves, and all of these deserve further investigation.24

In this report, the range in lOP, the diurnal variation in lOP, the time of the highest lOP, and the time ofthe lowest lOP were fourtd to be statistically similar in those eyes with and those without visual field defects. No lOP characteristics were identified that could reliably separate those with normal fields from those with abnormal fields. Therefore, regardless of how useful a diurnal lOP profile may be in providing individualized care for a patient, it does not appear to be useful in detecting cases in which visual field abnormalities have already occurred.

With present developments in automation and stan­dardization of testing, the data on large groups of patients from different laboratories can now be directly compared. It is hoped that this report will stimulate other studies so that comparisons between referral pop­ulations can be analysed and conclusions reached re­garding the proper method for glaucoma screening, as well as for detailed analyses of patients with glaucoma.

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