Does hormone replacement therapy influence retinal microvascular caliber?

Gender differences in ocular blood flow

Gender medicine has been a major focus of research in recent years. The present review focuses on gender differences in the epidemiology of the most frequent ocular diseases that have been found to be associated with impaired ocular blood flow, such as age-related macular degeneration, glaucoma and diabetic retinopathy. Data have accumulated indicating that hormones have an important role in these diseases, since there are major differences in the prevalence and incidence between men and pre- and post-menopausal women. Whether this is related to vascular factors is, however, not entirely clear. Interestingly, the current knowledge about differences in ocular vascular parameters between men and women is sparse. Although little data is available, estrogen, progesterone and testosterone are most likely important regulators of blood flow in the retina and choroid, because they are key regulators of vascular tone in other organs. Estrogen seems to play a protective role since it decreases vascular resistance in large ocular vessels. Some studies indicate that hormone therapy is beneficial for ocular vascular disease in post-menopausal women. This evidence is, however, not sufficient to give any recommendation. Generally, remarkably few data are available on the role of sex hormones on ocular blood flow regulation, a topic that requires more attention in the future.

Physical activity, television viewing time, and retinal vascular caliber

PURPOSE

to examine the associations of physical activity and television (TV) viewing time with retinal vascular caliber in Australian adults.

METHODS

a total of 2024 adults aged 25 yr or older without known diabetes in the Australian Diabetes, Obesity, and Lifestyle Study (AusDiab, 1999-2000), a population-based cross-sectional study, were evaluated. Retinal vascular calibers (both arteriolar and venular calibers) were measured from digital retinal photographs using a computer-assisted method and were summarized into central retinal artery and vein equivalents. Self-reported physical activity time and TV viewing time were obtained using interviewer-administered questionnaires.

RESULTS

for physical activity, no statistically significant multivariate relationships emerged for men or for women. After adjusting for confounders (age, sex, education, cigarette smoking, diet quality, waist circumference, systolic blood pressure, plasma glucose levels, serum fibrinogen, serum triglyceride, and physical activity time), men who watched TV for at least 2 h·d had a venular caliber that was 4.71 microm (95% confidence interval = 1.37-8.04 microm, P = 0.006) wider compared with those watching <2 h·d of TV. No significant association with venular caliber was noted in women.

CONCLUSIONS

these findings provide the first evidence of an association between TV viewing time (a common, leisure time sedentary behavior) and retinal microcirculation. Further research is needed to examine these associations in different populations and by using more comprehensive physical activity and sedentary behavior measures.

The associations between blood levels of homocysteine, folate, vitamin B12, and retinal vascular caliber

PURPOSE

To assess the association of total serum levels of homocysteine (tHcy), folate, and vitamin B12 with retinal vascular caliber in older adults.

DESIGN

Cross-sectional, population-based study.

METHODS

One thousand seven hundred and seventy-two of 2334 Blue Mountains Eye Study participants examined had fundus photographs taken and retinal arteriolar and venular caliber measured using computer-assisted techniques and summarized. Serum folate and vitamin B12 levels and tHcy were determined from venous blood samples. Linear regression models adjusting for age, gender, mean arterial blood pressure, smoking, and diabetes were used to assess whether serum levels of tHcy, folate, and vitamin B12 were associated with retinal arteriolar and venular caliber.

RESULTS

Arteriolar and venular caliber was not associated with tHcy in the total population. Further analysis demonstrated a significant serum homocysteine-gender interaction (P = .04). A significant inverse association between tHcy and arteriolar caliber was found in men only (P = .03), with a threshold detected at a level of 17 micromol/l. Above this threshold, increasing tHcy was linearly associated with narrower arteriolar caliber (0.86 microm reduction per 1.0 micromol/l increase in tHcy) in men, but no significant association was found below this threshold. No significant associations were observed between serum folate or vitamin B12 levels and either retinal vessel caliber.

CONCLUSIONS

Retinal vascular caliber is associated with tHcy in men but not women. This finding may reflect the stronger association between blood pressure and tHcy in men than in women.

Regular aspirin use and retinal microvascular signs: the Blue Mountains Eye Study

OBJECTIVE

Hypertension is closely related to microvascular abnormalities and there is increasing interest in agents that target the microvasculature. The effect of aspirin on the microvasculature has not been well studied. We examined the cross-sectional and longitudinal associations between regular aspirin use and retinal microvascular signs.

DESIGN AND METHODS

We digitized retinal photographs from participants of the Blue Mountains Eye Study cohort (1992-1994, n = 3654, aged over 49 years, and 1997-1999, n = 2335) and used a computer-assisted method to measure average retinal arteriolar and venular diameters. Information on the frequency of aspirin use was collected, with regular aspirin use defined as weekly or daily.

RESULTS

Regular aspirin users comprised 21.2% (n = 775) of the baseline population. At baseline and in individuals who were on one or more antihypertensive medication, regular aspirin use was found to be associated with retinal arterioles on average 3.6 mum (95% confidence interval 1.0, 6.2) wider than those of non-users or occasional aspirin users, after adjusting for age, blood pressure, smoking, diabetes, non-steroidal anti-inflammatory drug use and other variables. Increasing frequency of aspirin use was associated with increasing retinal arteriolar diameter (Ptrend < 0.01). At 5-year follow-up, regular users of aspirin and antihypertensive medication(s) had wider retinal arterioles than those who used aspirin less regularly. Neither antihypertensive medication use alone nor aspirin use alone was associated with wider retinal vessels.

CONCLUSION

Our finding of a possible association between the combined use of aspirin and antihypertensive agent(s) and wider retinal arteriolar diameter warrants further investigation into the effects of aspirin on the microvasculature.

Retinal Vascular Caliber and Migraine: The Blue Mountains Eye Study

OBJECTIVE

To assess whether migraine is associated with retinal microvascular caliber.

BACKGROUND

Migraine is believed to be associated with vascular disease, but few studies have investigated the relationship between structural microvascular changes and migraine.

DESIGN

Population-based cross-sectional study.

METHODS

Participants in the Blue Mountains Eye Study follow-up (1997 to 1999, n = 2,335, aged 54+) had retinal photographs taken. A computer-assisted method was used to measure average retinal arteriolar and venular diameters and calculate the arteriole-to-venule ratio. History of migraine was recorded by interview using International Headache Society criteria (1988).

RESULTS

Subjects giving a history of migraine without aura (n = 128) had narrower retinal arterioles than subjects giving a history of migraine with aura (n = 182) or subjects with no migraine history (n = 1619). After multivariate adjustment, mean retinal arteriolar diameter was 4.3 microm (95% confidence interval 0.5, 8.1) narrower in subjects reporting migraine without aura as compared to subjects with no migraine.

CONCLUSIONS

Individuals with a history of migraine without aura were more likely to have slightly narrower retinal arteriolar caliber than individuals without migraine. This relationship was not present for migraine with aura. These data support the hypothesis that microvascular disease may be associated with certain types of migraine.