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Diurnal intraocular Pressure
Diurnal Intraocular 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 3. Diurnal Variation in Intraocular Pressure (lOP)
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. 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.
2. 3.
The visual field analysis utilized the automated Oc· Iy repo rted .6' 9' 10 . as has been prev10us topus penmeter 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 . t y. 7' 14' 15 and to the 0 ctopus U sers ' soc1e 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 Range
Mean
With visual field defects (400 eyes: 5 measure8 to 57 mmHg 22.1 mmHg ments per eye) Without visual field defects (400 eyes: 5 measure8 to 50 mmHg 21.0 mmHg ments per eye)
Standard Deviation
±7.4 ±5.4
With visual field defects (400 eyes) Without visual field defects (400 eyes)
Variation in lOP
Mean~
lOP
Standard Deviation
1 to 20 mmHg
6.2 mmHg
±3.6
1 to 19 mmHg
5.5 mmHg
±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
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125
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100
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VOLUME 92
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NUMBER 7
175r-------------------------------------, - - With visual field defects
... ...>
Ul
150
- - - - Without visual field defects
125
~ 100
::;
Ill
:I
•
- - With visual field defects
150
Ul
•
75
Ill
~ z
25 0~----~----~----~----~------~--~
5:00 a.m. to 7:00 a.m.
7:00 a.m. to 9:00 a.m.
9:00 a.m. 11:00 a.m. 1:00 p.m. to to to 11:00 a.m. 1:00 p.m. 3:00 p.m.
50 25 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 1. The number of eyes are plotted against the time of the highest (peak) intraocular pressure.
Fig 2. The number of eyes are plotted against the time of the lowest (trough) intraocular pressure.
lOP of less than 23 mmHg on at least one of the five time periods tested.
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
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
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.
8.
9.
10.
11.
12.
13.
14.
15.
16.
REFERENCES
17. 18.
1. Henkind P, Leitman M, Weitzman E. The diurnal curve in man: new observations. Invest Ophthalmol 1973; 12:705-7. 2. Henkind P, Walsh JB. Diurnal variations in intraocular pressure; chronic open angle glaucoma; preliminary report. Trans Ophthalmol Soc NZ 1981; 33:18-20. 3. Phelps CD, Woolson RF, Kolker AE, Becker B. Diurnal variation in intraocular pressure. Am J Ophthalmol 1974; 77:367-77. 4. Drance SM. The significance of the diurnal tension variations in normal and glaucomatous eyes. Arch Ophthalmol 1960; 64:494501. 5. de Venecia G, Davis MD. Diurnal variation of intraocular pressure in the normal eye. Arch Ophthalrnol 1963; 69:752-7. 6. Fankhauser F, Spahr J, Bebie H. Some aspects of the automation of perimetry. Surv Ophthalmol1977; 22:131-41. 7. Li SG, Spaeth GL, Scimeca HA, et al. Clinical experiences with the
19. 20.
21.
22. 23. 24.
use of an automated perimeter (Octopus) in the diagnosis and management of patients with glaucoma and neurologic diseases. Ophthalmology 1979; 86: 1302-12. Worthen OM. Intraocular pressure and its diurnal variation. In: Heilmann K, Richardson KT, eds. Glaucoma; Conceptions of a Disease; Pathogenesis, Diagnosis, Therapy. Stuttgart: Georg Thieme, 1978; 54-66. Zuhlke G, Schmied U. Introduction into technique and clinical application of OCTOPUS perimetry. In: Proceedings, First International Meeting on Automated Perimetry System: OCTOPUS, Zurich. Zurich: lnterzeag AG Schlieren, 1979; 4-23. Bell JA, Feldon SE. Retinal microangiopathy; correlation of OCTOPUS perimetry with fluorescein angiography. Arch Ophthalmol1984; 102: 1294-8. Flammer J, Drance SM, Fankhauser F, Augustiny L. Differential light threshold in automated static perimetry; factors influencing shortterm fluctuation. Arch Ophthalrnol 1984; 102:876-9. Flammer J, Drance SM, Zulauf M. Differential light threshold; the short- and long-term fluctuation in patients with glaucoma, normal controls, and patients with suspected glaucoma. Arch Ophthalrnol 1984; 102:704-6. Flammer J, Drance SM, Schulzer M. The estimation and testing of the components of long-term fluctuation of the differential light threshold. Doc Ophthalmol Proc Ser 1983; 35:383-9. Caprioli J, Spaeth GL. Static threshold examination of the peripheral nasal visual field in glaucoma. In: Proceedings of the 3rd Octopus Users' Society Meeting. Denver, Colorado, 1984. LeBlanc RP. Peripheral nasal visual field defects in primary open angle glaucoma. In: Proceedings of the 3rd Octopus Users' Society Meeting. Denver, Colorado, 1984. Packer H, Deutsch AR, Deweese MW, et al. Efficiency of screening tests for glaucoma. JAMA 1965; 192:693-6. Lennon RG, Turnbull CD. Diurnal intraocular pressure variation in a glaucoma screening program. Arch Ophthalmol 1968; 80:714-7. Kolker AE, Hetherington J Jr. Becker-Shaffer's Diagnosis and Therapy of the glaucomas, 5th ed. StLouis: CV Mosby, 1983; 3-8. Kitazawa Y, Horie T. Diurnal variation of intraocular pressure in primary open-angle glaucoma. Am J Ophthalmol 1975; 79:557-66. Katavisto M, Sainrnalkivi J. Tonometry among persons over 40 years of age (results of a mass examination at the North Karelian Central Hospital). Acta Ophthalmol 1964; 42:370-7. Worthen OM. Effect of pilocarpine drops on the diurnal intraocular pressure variation in patients with glaucoma. Invest Ophthalmol 1976; 15:784-7. Levene RZ. Low tension glaucoma: a critical review and new material. Surv Ophthalmol 1980; 24:621-64. Worthen OM. Economic aspects of the management of ocular hypertension. Surv Ophthalmol 1980; 25:206-14. Levi L, Schwartz B. Glaucoma screening in the health care setting. Surv Ophthalmol 1983; 28:164-74.
861
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 3. Diurnal Variation in Intraocular Pressure (lOP)
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. 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.
2. 3.
The visual field analysis utilized the automated Oc· Iy repo rted .6' 9' 10 . as has been prev10us topus penmeter 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 . t y. 7' 14' 15 and to the 0 ctopus U sers ' soc1e 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 Range
Mean
With visual field defects (400 eyes: 5 measure8 to 57 mmHg 22.1 mmHg ments per eye) Without visual field defects (400 eyes: 5 measure8 to 50 mmHg 21.0 mmHg ments per eye)
Standard Deviation
±7.4 ±5.4
With visual field defects (400 eyes) Without visual field defects (400 eyes)
Variation in lOP
Mean~
lOP
Standard Deviation
1 to 20 mmHg
6.2 mmHg
±3.6
1 to 19 mmHg
5.5 mmHg
±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
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- - - - Without visual field defects
125
...0
100
...
75
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NUMBER 7
175r-------------------------------------, - - With visual field defects
... ...>
Ul
150
- - - - Without visual field defects
125
~ 100
::;
Ill
:I
•
- - With visual field defects
150
Ul
•
75
Ill
~ z
25 0~----~----~----~----~------~--~
5:00 a.m. to 7:00 a.m.
7:00 a.m. to 9:00 a.m.
9:00 a.m. 11:00 a.m. 1:00 p.m. to to to 11:00 a.m. 1:00 p.m. 3:00 p.m.
50 25 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 1. The number of eyes are plotted against the time of the highest (peak) intraocular pressure.
Fig 2. The number of eyes are plotted against the time of the lowest (trough) intraocular pressure.
lOP of less than 23 mmHg on at least one of the five time periods tested.
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
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
SMITH
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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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