Effect of seasons upon intraocular pressure in healthy population of China

Seasonal variations in anterior segment angle parameters in myopes and emmetropes

CLINICAL RELEVANCE

Seasonal variations are known to occur in a range of ocular parameters and in conditions including refractive error and glaucoma. It is of clinical importance to know if seasonal changes also occur in anterior segment angle parameters, given that they can influence these conditions.

BACKGROUND

The study aimed to examine the seasonal variations in anterior segment angle parameters in healthy young adults.

METHODS

Twenty-three emmetropic participants with a mean age of 26.17 ± 4.43 years and 22 myopic participants with a mean age of 27.27 ± 4.47 years completed four seasons of data collection. Anterior segment angle parameters were measured using swept-source anterior segment optical coherence tomography. Intraocular pressure (IOP) and objective refraction were also measured. Repeated-measures analysis of variance was used to determine the effect of season and refractive error on the various ocular parameters.

RESULTS

A significant main effect of season was found for the majority of anterior segment angle parameters, including the angle opening distance at 500 and 750 µm from the scleral spur (p = 0.02, p = 0.006, respectively), angle recess area at 500 and 750 µm from the scleral spur (both p = 0.002), and trabecular iris space area at 500 and 750 µm from the scleral (p = 0.02, p = 0.008, respectively). However, measures of anterior chamber depth and trabecular iris angle did not exhibit statistically significant seasonal variations (all p > 0.05). A significant main effect of season was also found for the changes in IOP (p = 0.004) and objective refraction (p < 0.001). There was no season by refractive group interaction for any anterior segment angle parameter or IOP (all p > 0.05).

CONCLUSION

There is a small but significant seasonal changes in the anterior segment angle parameters, refractive error, and IOP in healthy young adult males, in which the anterior segment angle dimensions are narrower, the IOP is higher, and the refraction is more myopic during winter.

Seasonal Variation and Trend of Intraocular Pressure Decrease Over a 20-Year Period in Normal-Tension Glaucoma Patients

PURPOSE

To investigate the trend of seasonal variation of intraocular pressure (IOP) in patients with normal-tension glaucoma over a 20-year period by retrospectively analyzing the Kyoto Prefectural University of Medicine Glaucoma Registry database as real-world data.

DESIGN

Retrospective cohort study.

METHODS

Data points (n = 49,007) were extracted retrospectively from the medical records of 1774 patients with normal-tension glaucoma (665 male patients and 1109 female patients; mean ± SD age was 59.8 ± 14.4 years; and mean ± SD observation period was 5.6 ± 4.4 years) seen over the 20-year period. We first calculated the mean IOP from all available data of each month from January 1997 through December 2016. The data were then categorized into 5 groups of 4 consecutive years each (1997-2000, 2001-2004, 2005-2008, 2009-2012, and 2013-2016) and the mean IOP of each month within the group was calculated. Seasonal variations of IOP over the 20-year study period and in the 5 consecutive groups were then investigated via nonlinear multiple regression analysis.

RESULTS

A continuous decrease of IOP was detected throughout the 20-year period (P < .001), with distinct seasonal variation. The annual mean ± SD IOP was highest (13.9 ± 2.7 mm Hg) in the oldest group (1997-2000), with a gradual decrease in each subsequent group, finally becoming lowest (12.3 ± 2.7 mm Hg) in the most recent group (2013-2016) (P < .001), and all of them were accompanied by distinct seasonal variation (P < .001).

CONCLUSIONS

Based on the Kyoto Prefectural University of Medicine Glaucoma Registry real-world longitudinal data, our findings revealed a continuous decrease and distinct seasonal variation of IOP in patients with normal-tension glaucoma throughout the 20-year study period.

Observation seasonal variation of intraocular pressure in young healthy volunteers

AIM

To investigate fluctuation of intraocular pressure (IOP) and seasonal variation of 24-hour IOP during one year in healthy participants.

METHODS

Totally 13 young healthy volunteers participated in this study. IOP was measured with Canon TX-20 at about 8:00-9:00 a.m. from Monday to Friday every week for a whole year. They also underwent 24-hour IOP examination every three months. Blood pressure, heart rate, temperature, humidity, atmosphere pressure, sunshine duration and other environment parameters were recorded.

RESULTS

The yearly fluctuation curve showed IOP in the summer months were lower than other seasons. In the multivariable generalized estimating equation analysis, IOP had a negative correlation with both temperature and sunshine duration (P<0.05). There also was a seasonal effect on 24-hour IOP. However, all intraclass correlation coefficients values of minimum, maximum and average of the 24-hour IOP and each individual IOP were less than 0.30.

CONCLUSION

IOP is trend to be higher in cold days than warm days. IOP have negative association with both environmental temperature and duration of sunshine. On a season-to-season basis, 24-hour IOP is not highly reproducible in healthy volunteers.

Time-of-Year Variation in Intraocular Pressure

PRÉCIS

In this study conducted in Chicago, IL, intraocular pressure (IOP) level was found to have a subtle, but measurable, annual pattern. Reasonable evidence is presented for a time-of-year variation in IOP. Adequate numbers of subjects must be studied to detect this small variation.

PURPOSE

The aim was to investigate the relationship between IOP and time of year.

METHODS

During a separate investigation, patients from 2011 to 2018 (dataset A, N=3041) in an urban, academic facility in Chicago, IL received an examination that included Goldmann applanation tonometry. Regression analyses assessed the relationship between time of year and IOP. Two additional datasets, 1 collected in a similar manner during 1999 and 2002 (dataset B, N=3261) and another consisting of all first visits during 2012 and 2017 (dataset C, N=69,858), were used to confirm and further investigate trends.

RESULTS

For dataset A, peak mean IOP occurred in December/January (15.7±3.7/15.7±3.8 mm Hg) and lowest in September (14.5±3.1 mm Hg). The analysis suggested conventional quarterly analysis (January to March, etc.) can conceal time-of-year relationships because of inadequate statistical power and timing of IOP variation. Multiple linear regression analysis, with a November-to-October reordering, detected an annual, downward IOP trend (P<0.0001). Analysis of dataset B confirmed this trend (P<0.001). Fourier analysis on datasets A and B combined supported a 12-month IOP cycle for right/left eyes (P=0.01/P=0.005) and dataset C provided stronger evidence for an annual periodicity (P<0.0001). Harmonics analysis of dataset C showed a repeating pattern where IOP trended downward around April, and then back upward around October.

CONCLUSIONS

This analysis strongly supports a demonstrable annual, cyclical IOP pattern with a trough to peak variation of ≈1 mm Hg, which has a seasonal relationship.

Seasonal fluctuation in intraocular pressure and its associated factors in primary open-angle glaucoma

BACKGROUND/OBJECTIVES

To evaluate seasonal fluctuations in intraocular pressure (IOP) in primary open-angle glaucoma (POAG) and its associated factors.

SUBJECTS/METHODS

POAG patients treated only with glaucoma eye drops were enroled. Winter and summer IOPs were evaluated. The Seasonal fluctuation rate of IOP was defined as follows: (mean winter IOP-mean summer IOP)/mean IOP in all seasons. Multiple linear regression analysis was used to explore factors associated with the seasonal IOP fluctuation rate including: age, gender, family history of glaucoma, type of glaucoma, number of eye drops, type of eye drops, mean deviation (MD) value, MD slope, disc haemorrhage, central corneal thickness and spherical equivalent.

RESULTS

Winter IOP was higher than summer IOP in 204 POAG eyes of 204 patients, including 162 eyes with normal tension glaucoma (NTG) (13.2 ± 2.7 vs. 12.0 ± 2.3 mmHg, P < 0.001). The mean age and follow-up duration were 63.3 ± 11.4 years and 140.0 ± 66.9 months. Initial MD and MD slope were -2.1 ± 3.4 dB and -0.07 ± 0.50 dB/year, respectively. POAG was positively associated with the rate of seasonal IOP fluctuations compared to NTG (β = 5.29, P = 0.013). Family history, and timolol and carteolol use were also factors associated with the IOP fluctuation rate (β = -6.27, P = 0.007; β = 4.94, P = 0.030; and β = 4.51, P = 0.042, respectively).

CONCLUSIONS

We confirmed seasonal IOP fluctuations in POAG. Type of glaucoma, family history of glaucoma, and β-blocker use might influence IOP fluctuations.

Associations Between Regional Environment and Cornea-Related Morphology of the Eye in Young Adults: A Large-Scale Multicenter Cross-Sectional Study

Purpose

To investigate environmental factors associated with corneal morphologic changes.

Methods

A cross-sectional study was conducted, which enrolled adults of the Han ethnicity aged 18 to 44 years from 20 cities. The cornea-related morphology was measured using an ocular anterior segment analysis system. The geographic indexes of each city and meteorological indexes of daily city-level data from the past 40 years (1980-2019) were obtained. Correlation analyses at the city level and multilevel model analyses at the eye level were performed.

Results

In total, 114,067 eyes were used for analysis. In the correlation analyses at the city level, the corneal thickness was positively correlated with the mean values of precipitation (highest r [correlation coefficient]: >0.700), temperature, and relative humidity (RH), as well as the amount of annual variation in precipitation (r: 0.548 to 0.721), and negatively correlated with the mean daily difference in the temperature (DIF T), duration of sunshine, and variance in RH (r: -0.694 to 0.495). In contrast, the anterior chamber (AC) volume was negatively correlated with the mean values of precipitation, temperature, RH, and the amount of annual variation in precipitation (r: -0.672 to -0.448), and positively associated with the mean DIF T (r = 0.570) and variance in temperature (r = 0.507). In total 19,988 eyes were analyzed at the eye level. After adjusting for age, precipitation was the major explanatory factor among the environmental factors for the variability in corneal thickness and AC volume.

Conclusions

Individuals who were raised in warm and wet environments had thicker corneas and smaller AC volumes than those from cold and dry ambient environments. Our findings demonstrate the role of local environmental factors in corneal-related morphology.

Seasonal Fluctuation in Intraocular Pressure and Retinal Nerve Fiber Layer Thinning in Primary Open-Angle Glaucoma

PURPOSE

To detect seasonal fluctuations in intraocular pressure (IOP) in healthy eyes and eyes with primary open-angle glaucoma (POAG) and to evaluate whether these seasonal fluctuations affect retinal nerve fiber layer (RNFL) thinning in eyes with POAG.

DESIGN

Observational, retrospective cohort study.

PARTICIPANTS

Healthy population who underwent a comprehensive health check-up and patients with POAG using only topical medications were enrolled.

METHODS

Kaplan-Meier survival analysis was used to compare the cumulative incidence probabilities of RNFL thinning between different seasonal IOP fluctuation groups. A Cox proportional hazards model, with adjustments for potential confounding factors, was used to evaluate the association between seasonal fluctuations in IOP and RNFL thinning.

MAIN OUTCOME MEASURES

Intraocular pressure fluctuation rate calculated from winter and summer IOPs and RNFL thinning as determined by event-based analysis with high-definition OCT.

RESULTS

A total of 12 686 healthy eyes and 179 eyes of 179 POAG patients showed a significantly higher IOP in winter than in summer (healthy, 13.2 ± 3.0 mmHg vs. 12.5 ± 2.9 mmHg [P < 0.001]; POAG, 13.1 ± 2.7 mmHg vs. 11.8 ± 2.3 mmHg [P < 0.001]). In POAG patients, the mean age at initial OCT and follow-up duration were 55.1 ± 11.7 years and 98.4 ± 26.4 months, respectively. The mean deviation (MD) at first visit, MD slope, and RNFL thinning rate were -2.2 ± 3.4 dB, -0.07 ± 0.44 dB/year, and -0.44 ± 0.88 μm/year, respectively. During the study period, 85 eyes (47.5%) showed RNFL thinning progression. Kaplan-Meier analysis showed that a high seasonal IOP fluctuation rate significantly suppressed RNFL thinning (P < 0.05, log-rank test). After adjusting for confounders in the Cox analysis, the seasonal IOP fluctuation rate still showed a significantly negative association with RNFL thinning (hazard ratio, 0.98; 95% confidence interval, 0.96-0.99; P = 0.005).

CONCLUSIONS

Winter IOP was higher than summer IOP in both healthy and POAG eyes. The temporary IOP decline in summer, rather than a constant IOP throughout the year, may prevent glaucoma progression.

Tear Break-Up Time and Seasonal Variation in Intraocular Pressure in a Japanese Population

PURPOSE

To evaluate seasonal variation in intraocular pressure (IOP) with and without short tear break-up time (SBUT, BUT ≤5 s) since dry eye and IOP are known to have seasonal variation.

METHODS

This study enrolled 176 patients who visited one of six eye clinics, in Japan, four times for IOP measurement, in every season. The mean patient age was 67.9 years, including 79 males. Participants were divided into four groups based on the presence of glaucoma and/or SBUT and we compared the seasonal variation in IOP (winter and summer) among the four groups.

RESULTS

The IOP (mmHg) in winter and summer, respectively, was 12.8 ± 3.7 and 12.8 ± 3.1 for non-glaucoma patients without SBUT (n = 47, p = 0.964), 14.8 ± 3.4 and 13.3 ± 3.4 for non-glaucoma patients with SBUT (n = 57, p < 0.001), 14.3 ± 3.2 and 14.1 ± 3.4 for glaucoma patients without SBUT (n = 36, p = 0.489), and 13.3 ± 3.0 and 11.6 ± 2.9 for glaucoma with SBUT (n = 36, p < 0.001). Seasonal variation was largest across the seasons in the glaucoma with the SBUT group, and the magnitude of seasonal variation correlated with BUT (β = 0.228, p = 0.003).

CONCLUSIONS

Seasonal variation tended to be larger in patients with SBUT than those without SBUT.

Reduced humidity experienced by mice in vivo coincides with reduced outflow facility measured ex vivo

Mice are routinely used to study aqueous humour dynamics. However, physical factors such as temperature and hydration affect outflow facility in enucleated eyes. This retrospective study examined whether differences in temperature and relative humidity experienced by living mice within their housing environment in vivo coincide with differences in outflow facility measured ex vivo. Facility data and environmental records were collected for one enucleated eye from 116 mice (C57BL/6J males, 9-15 weeks old) at two institutions. Outflow facility was reduced when relative humidity was below the lower limit of 45% recommended by the UK Code of Practice, but there was no detectable effect of temperature on outflow facility. Even when accounting for effects of humidity, there were differences in outflow facility measured between institutions and between individual researchers at the same institution. These data indicate that humidity, as well as additional environmental factors experienced by living mice within their housing environment, may significantly affect outflow facility measured ex vivo.

Cyclic Pattern of Intraocular Pressure (IOP) and Transient IOP Fluctuations in Nonhuman Primates Measured with Continuous Wireless Telemetry

Purpose: Most studies on intraocular pressure (IOP) to monitor IOP "fluctuations" in glaucoma patients have been performed with snapshot tonometry techniques that obtain IOP measurements at single time points weeks to months apart. However, IOP telemetry has shown that IOP varies from second-to-second due to blinks, saccades, and systolic vascular filling. The purpose of this study was to characterize the cyclic pattern of baseline IOP and transient IOP fluctuations in 3 nonhuman primates (NHPs).Methods: Bilateral IOP was measured using a proven implantable telemetry system and recorded 500 times per second, 24 hours a day, up to 451 continuous days in 3 male rhesus macaques aged 4 to 5 years old. The IOP transducers were calibrated every two weeks via anterior chamber cannulation manometry and all data were continuously corrected for signal drift via software, filtered for signal noise and dropout, and peaks and troughs were quantified and counted using a finite impulse response filter; waking hours were defined as 6:00-18:00 hours based on room light cycle.Results: Fourier transform analyses of baseline IOP and the hourly mean frequency of transient IOP fluctuations > 0.6 mmHg, 0.6-5 mmHg and > 5 mmHg above baseline during waking hours exhibited an approximate 16- to 91-day cyclic pattern in all NHPs. There were no measured environmental or experimental factors associated with this cyclical pattern.Conclusions: While the importance of the cyclic pattern identified in IOP and its fluctuations is unknown at this time, it is plausible that this pattern is relevant to both homeostasis and pathophysiology of the ONH, corneoscleral shell, and aqueous outflow pathways.

Genetic correlations between intraocular pressure, blood pressure and primary open-angle glaucoma: a multi-cohort analysis

Primary open-angle glaucoma (POAG) is the most common chronic optic neuropathy worldwide. Epidemiological studies show a robust positive relation between intraocular pressure (IOP) and POAG and modest positive association between IOP and blood pressure (BP), while the relation between BP and POAG is controversial. The International Glaucoma Genetics Consortium (n=27 558), the International Consortium on Blood Pressure (n=69 395), and the National Eye Institute Glaucoma Human Genetics Collaboration Heritable Overall Operational Database (n=37 333), represent genome-wide data sets for IOP, BP traits and POAG, respectively. We formed genome-wide significant variant panels for IOP and diastolic BP and found a strong relation with POAG (odds ratio and 95% confidence interval: 1.18 (1.14-1.21), P=1.8 × 10^-27) for the former trait but no association for the latter (P=0.93). Next, we used linkage disequilibrium (LD) score regression, to provide genome-wide estimates of correlation between traits without the need for additional phenotyping. We also compared our genome-wide estimate of heritability between IOP and BP to an estimate based solely on direct measures of these traits in the Erasmus Rucphen Family (ERF; n=2519) study using Sequential Oligogenic Linkage Analysis Routines (SOLAR). LD score regression revealed high genetic correlation between IOP and POAG (48.5%, P=2.1 × 10^-5); however, genetic correlation between IOP and diastolic BP (P=0.86) and between diastolic BP and POAG (P=0.42) were negligible. Using SOLAR in the ERF study, we confirmed the minimal heritability between IOP and diastolic BP (P=0.63). Overall, IOP shares genetic basis with POAG, whereas BP has limited shared genetic correlation with IOP or POAG.

Seasonal changes of 24-hour intraocular pressure rhythm in healthy Shanghai population

The aim of the present study was to investigate and compare the 24-hour intraocular pressure (IOP) rhythms in winter and summer in the healthy population of Shanghai, China.This is a cross-sectional study in which 24-hour IOP measurements were taken for all eligible healthy volunteers in winter and summer, respectively, and the temperature, hours of sunlight (sunlight time), and circulatory parameters, including heart rate, systolic blood pressure, and diastolic blood pressure, were also recorded. The 24-hour IOP curves and IOP parameters (mean, peak, trough, and fluctuation of IOP together with the diurnal-to-nocturnal IOP change) in winter and summer were obtained and compared. The magnitude of IOP changes from summer to winter was also calculated.A total of 29 participants (58 eyes), 14 (48.28%) male and 15 (51.72%) female, aged 43.66 ± 12.20 (19-61) years, were considered eligible for this study. Generally, IOP decreased progressively before noon, increased notably in the nocturnal period, and peaked at 12:00 AM in winter and at 2:00 AM in summer. The pattern of 24-hour IOP in winter and summer was significantly different (P = 0.002). The average IOPs from 4:00 PM to 8:00 AM, except for 6:00 AM, were significantly higher in winter (P < 0.05). However, no significant differences were shown after adjusting for temperature and/or sunlight time. From summer to winter, the extent of IOP increase was mostly around 0 to 3 mm Hg, and the IOPs increased more significantly in the nocturnal period than in the diurnal period (P = 0.05).The 24-hour IOP rhythms were different in winter and summer, with higher IOP level in winter. Temperature and sunlight time, which are independent of heart rate and blood pressure, affected the 24-hour IOP rhythms in healthy people in Shanghai, China. Further investigations are expected for the rhythm of some endogenous substance secretion and the inner mechanism of regulation of IOP.

Associations with Intraocular Pressure in a Large Cohort: Results from the UK Biobank

PURPOSE

To describe the associations of physical and demographic factors with Goldmann-correlated intraocular pressure (IOPg) and corneal-compensated intraocular pressure (IOPcc) in a British cohort.

DESIGN

Cross-sectional study within the UK Biobank, a large-scale multisite cohort study in the United Kingdom.

PARTICIPANTS

We included 110 573 participants from the UK Biobank with intraocular pressure (IOP) measurements available. Their mean age was 57 years (range, 40-69 years); 54% were women, and 90% were white.

METHODS

Participants had 1 IOP measurement made on each eye using the Ocular Response Analyzer noncontact tonometer. Linear regression models were used to assess the associations of IOP with physical and demographic factors.

MAIN OUTCOME MEASURES

The IOPg and IOPcc.

RESULTS

The mean IOPg was 15.72 mmHg (95% confidence interval [CI], 15.70-15.74 mmHg), and the mean IOPcc was 15.95 mmHg (15.92-15.97 mmHg). After adjusting for covariates, IOPg and IOPcc were both significantly associated with older age, male sex, higher systolic blood pressure (SBP), faster heart rate, greater myopia, self-reported glaucoma, and colder season (all P < 0.001). The strongest determinants of both IOPg and IOPcc were SBP (partial R(2): IOPg 2.30%, IOPcc 2.26%), followed by refractive error (IOPg 0.60%, IOPcc 1.04%). The following variables had different directions of association with IOPg and IOPcc: height (-0.77 mmHg/m IOPg; 1.03 mmHg/m IOPcc), smoking (0.19 mmHg IOPg, -0.35 mmHg IOPcc), self-reported diabetes (0.41 mmHg IOPg, -0.05 mmHg IOPcc), and black ethnicity (-0.80 mmHg IOPg, 0.77 mmHg IOPcc). This suggests that height, smoking, diabetes, and ethnicity are related to corneal biomechanical properties. The increase in both IOPg and IOPcc with age was greatest among those of mixed ethnicities, followed by blacks and whites. The same set of covariates explained 7.4% of the variability of IOPcc but only 5.3% of the variability of IOPg.

CONCLUSIONS

This analysis of associations with IOP in a large cohort demonstrated that some variables clearly have different associations with IOPg and IOPcc, and that these 2 measurements may reflect different biological characteristics.

Changes in intraocular pressure after pharmacologic pupil dilation

Background

Intraocular pressure (IOP) may vary according to the change of ocular conditions. In this study, we want to assess the effect and mechanism of pupil dilation on IOP in normal subjects.

Methods

We prospectively evaluated 32 eyes of 32 patients (age; 61.7 ± 8.2 years) with normal open angles under diurnal IOP. IOP was measured every two hours from 9 AM to 11 PM for one day to establish baseline values and was measured again for one day to assess the differences after dilation. To induce dilation, we administered 2.5% phenylephrine and 1% tropicamide every 5 minutes from 8:30 AM to 8:45 AM and for every two hours from 11 AM to 9 PM to keep the pupil dilated. Diurnal IOP, biometry, Visante OCT, and laser flare photometry were measured before and after dilation.

Results

We observed a significant increase in IOP after dilation, 1.85 ± 2.01 mmHg (p = 0.002). IOP elevation remained significant until about four hours after dilation. Thereafter, IOP decreased slowly and eventually reached pre-dilation level (p > 0.05). Flare values decreased, and the anterior chamber angle became wider after mydriasis.

Conclusions

Dilation of the pupil significantly and incidentally elevated IOP in normal subjects. Further related studies are warranted to characterize the mechanism of the increased IOP after dilation.

The Effect of Aerobic Exercise on Intraocular Pressure in Horse

The present study was planned to investigate the effect of the intensity of exercise on intraocular pressure (IOP), systolic and diastolic blood pressure, glycaemia and blood lactate concentration in regularly trained Italian saddle jumper horses. On the first day five female horses performed 1 h of walking on an electronically controlled horse-walker at 100 m/min; on the second day 1 h session consisted of 5 min of walk, 30 min of trot, 20 min of gallop and one exercise of a 300 m long trail with eight jumps 90 cm high to be run in 1 min. The studied indicators were collected at rest, immediately after the exercise and 30 min after the exercise. Analysis of variance (ANOVA) showed a significant effect of different workloads on blood lactate concentration, systolic and diastolic blood pressure. No significant difference was found in IOP reduction when comparing aerobic and moderate anaerobic exercise. Our results confirm that the lack of a significant change in IOP in the athletic horse after mild exercise is in accordance with the human athlete. The cardiovascular and haematological changes induced by aerobic and moderate anaerobic exercise had no significant effect on IOP, either.

Morphologic changes in the outflow pathways of bovine eyes treated with corticosteroids

PURPOSE

To analyze morphologic changes in the trabecular meshwork (TM) of bovine eyes treated with topical prednisolone and exhibiting elevated intraocular pressure for 4 weeks.

METHODS

The TM of four adult Braford cow eyes treated with 0.5% prednisolone eye drops three times daily for 7 weeks and their contralateral eyes treated with artificial tear preparation and that of two adult untreated Braford cows and untreated young calves eyes were analyzed with light and electron microscopy. Increased extracellular matrix (ECM) under the outflow loops was evaluated quantitatively. Additionally, deparaffinized tissue of treated eyes was labeled with an antibody against type VI collagen for immunocytochemistry.

RESULTS

In steroid-treated eyes ECM (plaques) accumulated under the endothelium of the inner wall of the outflow loops. On electron microscopy, this material contained fine fibrils that labeled for type VI collagen. Plaques were also seen in the contralateral controls of the treated animals but here they were significantly less in amount. In the untreated Braford controls and in untreated calf eyes, plaques were nearly absent. In the TM cells of the treated eyes there was a loss of glycogen from the cytoplasm and an increase in basement membrane-like material. These changes were not seen in contralateral eyes or eyes of untreated animals.

CONCLUSIONS

Accumulations of ECM in the treated eyes resembled morphologic changes in human eyes with primary open-angle glaucoma and steroid-induced glaucoma. This animal model, therefore, provides a good tool in which to further study the pathogenesis of TM changes in glaucoma.