Twenty-four-hour pattern of mouse intraocular pressure

The 24-hr pattern of intraocular pressure in the mouse eye remains poorly characterized. The present study was undertaken to determine the magnitude, dynamic pattern, and synchrony of the 24-hr pattern of intraocular pressure (IOP) in NIH Swiss mice exposed to a 12-hr light/dark cycle or to constant light. IOP was measured every 3 hr using a microneedle method. Mice exposed to a 12-hr light /dark cycle were either measured repeatedly at 1 week interval (group 1) or were only measured once (group 2). A third group was exposed to constant light for 2 weeks prior to IOP measurements. The 24-hr IOP pattern in the first and second groups showed a similar rhythmic pattern that appeared to be sinusoidal. This IOP pattern declined in the morning until 12:00, and then increased in the early evening until 21:00. In contrast, IOP in the third group was asynchronous with some mice exhibiting multiple peaks and troughs during the 24-hr period. These results show that 24-hr IOP pattern in mouse eyes is biphasic and that extended exposure to constant light disrupts this 24-hr IOP pattern.     

Twenty-four-hour intraocular pressure pattern associated with early glaucomatous changes

PURPOSE: To characterize the 24-hour pattern of intraocular pressure (IOP) in untreated patients with newly diagnosed early glaucomatous changes. METHODS: Measurements of IOP, blood pressure, and heart rate were taken every 2 hours during a 24-hour period from a group of 24 untreated patients (ages 40-78 years) with newly diagnosed abnormal optic discs and/or abnormal visual fields. In the 16-hour diurnal awake period, IOP was measured sitting and supine, and blood pressure and heart rate were measured supine. In the 8-hour nocturnal sleep period, all measurements were taken in the supine position. Mean diurnal and nocturnal IOP, blood pressure, and heart rate in the glaucoma group were compared with data obtained from an age-matched control group of 24 individuals with healthy eyes. RESULTS: Mean diurnal IOP, either sitting or supine, was significantly higher in the glaucoma group than in the control group. For both subject groups, nocturnal supine IOP was higher than diurnal sitting IOP. However, this diurnal-to-nocturnal increase in IOP was significantly smaller in the glaucoma group. When compared with the diurnal supine IOP, the nocturnal supine IOP was lower in the glaucoma group but higher in the control group. Around normal awakening time, the supine IOP increased in the glaucoma group and did not change in the control group. There was a diurnal-to-nocturnal decrease in mean blood pressure only in the glaucoma group. CONCLUSIONS: Compared with healthy eyes, the diurnal IOP is higher, the diurnal-to-nocturnal change of habitual IOP is less, and the posture-independent IOP pattern around normal awakening time is different in eyes with early glaucomatous changes.     

Twenty-four-hour pattern of intraocular pressure in young adults with moderate to severe myopia

PURPOSE: To characterize the 24-hour change of intraocular pressure (IOP) in young adults with moderate to severe myopia. METHODS: Nineteen young adults, ages 18 to 25 years, with moderate to severe myopia (myopia group) and 17 age-matched volunteers with emmetropia or mild myopia (control group) were housed for 1 day in a sleep laboratory. An 8-hour accustomed sleep period was assigned to each volunteer. Twelve measurements of IOP, axial length, blood pressure, and heart rate were taken at 2-hour intervals. In the wake period, blood pressure and heart rate were measured after a 5-minute bed rest. Axial length and IOP were measured in supine volunteers. Volunteers then sat for 5 minutes, after which IOP was measured. In the sleep period, measurements were taken in supine volunteers in bed. RESULTS: In both the myopia and control groups, the average supine IOP in the sleep period was higher than the average sitting IOP in the wake period. However, the magnitude of this IOP elevation at night was significantly less in the myopia group. In the sleep period, IOP was less in the myopia group than in the control group. When only the 24-hour supine IOP data were considered, the trough occurred at 1:30 AM, and the peak occurred around noon in the myopia group. In the control group, the trough was at 9:30 PM, and the peak at 5:30 AM. Least-square cosine fits showed 24-hour rhythms of supine IOP in both groups, but their phase timings were different. Axial length remained unchanged throughout the day and night in both groups. There was no difference in the 24-hour rhythms of mean blood pressure and heart rate between the two groups. CONCLUSIONS: Considering habitual body positions, IOP increases at night in young adults with moderate to severe myopia, but the magnitude of the increase is significantly less than that in the age-matched control subjects. There is a 24-hour rhythm of supine IOP in the myopic group, but the phase timing is different from that in the control subjects. These variations of IOP in young adults with moderate to severe myopia are not related to changes in cardiovascular parameters.     

Evaluation of intraocular pressure in a pediatric population.

The purpose of this study was to examine the intraocular pressure (IOP) in a pediatric population without general anesthesia, and compare it to the IOP in a normal adult population. Little information is available on the normal IOP in a pediatric population. IOP was measured in a sample of 212 eyes (111 patients) using the Keeler Pulsair Hand Held Non-Contact Tonometer to determine the range of IOP in this population. Patients ranged in age from 7 months to 5 years, 10 months. The mean IOP of each eye was based on three readings. These IOP values were grouped by the chronological age of the children. The results support the conclusion that infant/toddler patients have lower mean IOP than adults and that as age increases, IOP increases.     

Epidemiology of intraocular pressure in a population screened for glaucoma.

This study evaluated the association between intraocular pressure and various sociodemographic characteristics, ocular findings, and cardiovascular risk factors in a population screened for glaucoma. A total of 2594 subjects older than 40 years residing in three urban areas of southern Israel participated. Of those screened 6.1% had a raised intraocular pressure (IOP greater than or equal to 21). The mean IOP increased with age, was higher among persons born in Africa or Asia than those born in Europe or America, higher among myopes than hypermetropes and among those with an enlarged cup-disc ratio (CDR). Analysis of variance tests indicated that refractive status, CDR, age, country of birth, and diabetes were each independently associated with IOP. In addition, associations between raised intraocular pressure and age, country of birth, myopia, CDR, diabetes, and glaucoma in the family were found.     

The pattern of distribution of intraocular pressure in the albino rabbit

The distribution pattern of intraocular pressure (IOP) was studied in a population of normal albino rabbits to find out whether IOP is Gaussian or distributed log-normally. The average IOP was 17.5 ± 3.1 mmHg (mean ± SD,n = 175) with a coefficient of variation of 17.7%. Using optimized graphical analysis, it was found that the IOP in the rabbit is distributed log-normally. This is in good agreement with the conclusions obtained in a recent study of normal human subjects, using the same analytical procedures. The diurnal variations in IOP cannot be a major contributing factor to the log-normal pattern of distribution of IOP in the albino rabbit, since a log-normal pattern of distribution was observed after the exclusion of the evening (high IOP) data.     

Twenty-four-hour time course of intraocular pressure in healthy and glaucomatous Africans: relation to sleep patterns

OBJECTIVE: The study was performed in early middle-aged African natives with primary open-angle glaucoma to compare the 24-hour intraocular pressure (IOP) variations in healthy versus young glaucoma patients, because IOP follows a circadian (24-hour) oscillation in healthy Caucasians. DESIGN: Case-control study. PARTICIPANTS: Sixteen healthy African volunteers (age 24.5 +/- 1 years, mean +/- standard error of the mean) and 11 open-angle glaucoma African patients (age 36.2 +/- 3.3 years). METHODS: IOP was measured hourly during 24 hours with a Modular One pneumatonometer (Modular One, Digilab, Cambridge, MA), which allows measures in supine subjects. To allow the IOP measurement at night, subjects were awakened under polysomnography (electroencephalogram, electromyogram, electro-oculogram) recorded at night and during a 90-minute afternoon nap. MAIN OUTCOME MEASURES: Hourly IOP values were analyzed for circadian rhythmicity with the Cosinor technique and in relation to the state of wakefulness, light sleep (stages 1 and 2), slow-wave sleep (stages 3 and 4), and rapid eye movement (REM) sleep upon awakening. RESULTS: Sleep patterns did not differ between patients and healthy volunteers. As expected, in the healthy subjects, IOP followed a 24-hour rhythm with a nocturnal peak value (acrophase), and the variations in IOP during sleep were related to sleep structure, being lowest during REM sleep and highest during slow-wave sleep. In the glaucoma patients, however, the 24-hour rhythm of IOP was reversed, with an afternoon acrophase and an early morning trough. CONCLUSIONS: These data suggest a circadian phase shift in IOP in glaucoma patients, with maintained relation to sleep structure.     

Caffeine and intraocular pressure in a Nigerian population

PURPOSE: Caffeine is widely consumed as kola nuts and in other products in sub-Saharan Africa. We examined the acute effect of caffeine on the intraocular pressures of healthy Nigerian volunteers between the ages of 20 and 27 years. METHODS: Intraocular pressure and blood pressure were measured 0, 30, 60, and 90 minutes after the ingestion of coffee by two groups of participants, namely the experimental (caffeinated coffee) and control (decaffeinated coffee) groups. RESULTS: The result showed that ingested caffeine increases intraocular pressure and that the elevation, though variable across patients, is sustained for several minutes. The mean increase across patients rises monotonically with the postingestion time and by almost 4 mm Hg. There was also a corresponding increase in systolic and diastolic blood pressure of the caffeinated group. There was relatively no change in intraocular pressure or blood pressure with time in the control group. The difference between both groups was statistically significant (P < 0.05). CONCLUSIONS: The results suggest the need for more glaucoma screenings and proper patient education, particularly in Nigerian populations in which the consumption of caffeine, contained in kola nuts and in other raw and processed products, is endemic and long-term.     

Physiological variables affecting intraocular pressure in a population study

Intraocular pressure (IOP) and several other parameters were measured on 560 subjects as part of a vision and health screening program. The sample included a large proportion of American Indians with diabetes (15.2%) and obesity. Multiple regression analysis showed that the percentage of ideal body weight index and average blood pressure both had independent effects on IOP, whereas age, blood sugar, sex, degree of Indian blood, and diabetes did not, although the latter three variables narrowly missed having a statistically significant effect in at least one eye. The analysis of variance showed that diabetes was associated with elevated IOP. This association was independent of random blood sugar, blood pressure, obesity index, and age.     

Corneal-compensated intraocular pressure,Goldmann-correlated intraocular pressure and their associated factors in the geriatric population,a population-based study

International Ophthalmology - To determine the distribution of corneal-compensated intraocular pressure (IOPcc), Goldmann-correlated intraocular pressure (IOPg) and their associated factors in a...     

The pattern evoked electroretinogram associated with elevated intraocular pressure

Electroretinographic responses to pattern-reversal stimuli (P-ERG) were recorded in eight patients with protracted elevation of intraocular pressure. Pressures of bigger than 30 mm Hg result in marked amplitude reductions in the P-ERG. The observed changes probably reflect the impaired function of retinal ganglion cells caused by decreased oxygen supply.     

New epidemiologic approach to intraocular pressure in an Antananarivo population

PURPOSE: The Malagasy population is a mixture from many ethnic origins. The Merina population is generally of Asiatic origin. The purpose of this study was to report the main characteristics of Merina intraocular pressure and their risk factors. METHODS: Screening was conducted in 1507 apparently healthy subjects with no known ocular disease (such as glaucoma) living in Antananarivo. Intraocular pressure was measured with a Goldmann tonometer. RESULTS: Males predominated (54.81%). The distribution of aplanation pressure followed an asymmetrical Gaussian pattern. In the Merina population, mean intraocular pressure was low (13.50+/-3.5mmHg, m+/-SD) and increased with age. There was no difference by gender. The prevalence of ocular hypertension was 1.43%. It was slightly higher in females and increased to the age of 50 years, then decreased. Among possible risk factors, only familial glaucoma was significantly frequent. CONCLUSION: The mean intraocular pressure in the Merina population is lower than the accepted statistical mean and is similar in both sexes. The prevalence of intraocular hypertension is also low but glaucoma develops early. Some of our data are similar to those observed in western populations (mean intraocular pressure increases with age). Other points are similar to the Asian population (low mean intraocular pressure and low frequency of intraocular hypertension and its progression after 50 years).     

Relationship between intraocular pressure and systemic health parameters in the Korean population

This study examined the influence of age, sex, blood pressure, and obesity index on intraocular pressure (IOP), in order to investigate the relationship between the upper limits of the following two conditions in the general Korean population: the "systolic or diastolic hypertensive and obese" group and the "systolic or diastolic hypotensive and lean" group. A total of 6828 healthy subjects (13,656 eyes) underwent automated multi-phasic tests, including tonometry, blood pressure, visual field, and body mass index. The 6,828 subjects were divided into five groups based on age; less than 40, 40 to 49, 50 to 59, 60 to 69, and over 70 years old. They were also divided into four categories on the basis of sex, age, blood pressure, and obesity index. The mean IOP in males (15.8+/-3.3 mmHg) was significantly higher than in females (14.8+/-3.1 mmHg) (P < 0.05), but this difference decreased proportionally with increasing age. IOP had a tendency to decrease with increasing age (P < 0.05). IOP increased significantly with increasing systolic blood pressure, diastolic blood pressure and obesity index (all, P < 0.05). The mean IOP of the "systolic or diastolic hypertensive and obese" group was higher than that of the "systolic or diastolic hypotensive and lean" group in the general Korean population (P < 0.05). These data could aid investigation into the epidemiological, etiologic and oriental influences related to the risk factors of glaucoma, especially in oriental populations.