Association of HYPERTENSION and GLAUCOMA

 

 

DR. SHIBRA FAROOQ

P.G. SCHOLAR

DEPARTMENT OF ILAJ-BIT-TADBEER

AJMAL KHAN TIBBIYA COLLEGE,

ALIGARH MUSLIM UNIVERSITY, INDIA

 

This post discusses two meta-analyses that analyze the association of hypertension with glaucoma.

META-ANALYSIS 1:

Bae HW, Lee N, Lee HS, Hong S, Seong GJ, Kim CY. Systemic hypertension as a risk factor for open-angle glaucoma: a meta-analysis of population-based studies. PLoS One. 2014 Sep 25;9(9):e108226. doi: 10.1371/journal.pone.0108226. PMID: 25254373; PMCID: PMC4177901.

The association between hypertension and glaucoma is controversial. It is usually assumed that hypertension increases the risk of development and progression of glaucoma.

In the Blue Mountains Eye Study, hypertension increased the risk of open-angle glaucoma (OAG) by more than 50%. The Egna-Neumarkt Study also found an association between OAG and hypertension. However, the Barbados Eye Study did not find an association between the two.

Hypertension can cause damage to the optic nerve through multiple mechanisms. These include direct microvascular damage, impairing the blood flow to the anterior optic nerve; auto-regulation of the posterior ciliary circulation; and induction of hypotensive episodes, especially at night, by anti-hypertensive therapy, which can injure the optic nerve.

A meta-analysis to look into systemic hypertension as a risk factor for OAG was performed by Bae et al. The meta-analysis included 16 studies involving 60,084 individuals.

The present meta-analysis of population-based studies showed that individuals with hypertension have an approximately 1.2-fold higher risk of developing OAG than individuals without hypertension. The pooled odds ratio (OR) was 1.22 (95% CI: 1.09–1.36) using the fixed-effects model and 1.22 (95% CI: 1.08–1.37) using the random-effects model.

The study found that hypertension increased the risk of OAG development irrespective of age.

The risk of developing high-tension glaucoma (HTG) was increased to a greater extent by hypertension than that of OAG, whereas the risk of developing normal-tension glaucoma (NTG) was not affected by hypertension (OR=1.92 and 0.94, respectively). This difference might be attributable to the difference in IOP, which is related to ocular perfusion pressure (OPP).

There are two conflicting mechanisms involving hypertension and glaucoma. Increased BP leads to reduced ocular blood flow due to thickening and stiffening of the vessel wall, thereby increasing the risk of OAG. The second mechanism is that a higher BP produces a higher OPP, which could decrease the risk of OAG.

No significant regional differences between Eastern and Western populations were noted.

META-ANALYSIS 2:

Nislawati R, Taufik Fadillah Zainal A, Ismail A, et al. Role of hypertension as a risk factor for open- angle glaucoma: a systematic review and meta-analysis. BMJ Open Ophthalmology 2021;6:e000798. doi:10.1136/ bmjophth-2021-000798.

The relationship between blood pressure (BP) and the incidence of glaucoma is still being debated.

Several studies have reported that BP and intraocular pressure (IOP) are directly related. This is because elevated BP increases episcleral venous pressure so that the aqueous outflow decreases, leading to an increase in IOP.

However, in younger patients, systemic hypertension (HTN) has a protective effect by increasing the ocular perfusion pressure (OPP).

A meta-analysis by Nislawati et al has shown that individuals with systemic HTN had a significantly 1.71- fold risk of developing glaucoma compared with non-hypertensive people (1.71 (95% CI 1.58 to 1.85)).

It is reported that a 10 mm Hg increase in systolic BP resulted in an increase in IOP by 0.26 mm Hg, whereas an increase in diastolic BP by 5 mm Hg increased IOP by 0.17 mm Hg.

The average age of patients with open-angle glaucoma (OAG) was higher with a mean difference result (4.21 (95% CI 0.7 to 7.72)). The results of another meta-analysis showed that the female gender had a higher risk of experiencing OAG with the result of a risk ratio (1.3 (95% CI 1.2 to 1.41)). This shows that HTN, age, and gender also contribute to the incidence of OAG.

High BP can increase IOP through two mechanisms, first, an increase in the production of aqueous humor, which is caused by an increase in capillary pressure in the ciliary body, thereby increasing the intravascular pressure and IOP gradient; second, decreasing the absorption of aqueous humor by increasing the episcleral venous pressure which obstructs the outflow of aqueous humor from the eye.

In hypertensive patients, glaucoma damage can also occur due to decreased perfusion pressure causing ischemia of the optic nerve or retinal ganglion cells (RGCs). HTN causes a narrowing of the caliber of the central retinal artery (CRA), which results in impaired flow to the eye, especially in the ocular nerve head and lamina cribrosa.

Unlike the positive effect of hypertension in younger patients, chronic elevated BP in the elderly increases the risk of arteriosclerosis, changes in precapillary arteriolar size leading to increased resistance to blood flow and resulting in decreased perfusion in the posterior segment of the eye, thereby counteracting the protective effect prevailing at younger ages.

Hypertension can cause autoregulation disorders resulting from an imbalance in endothelin-1 levels.

The analysis found that decreased Diastolic BP (DBP) can reduce perfusion pressure in the eye, which increases the risk of OAG. These studies show that individuals with unstable DBP, either high DBP or low DBP, are at increased risk of OAG.

CONCLUSION:

These meta-analyses which analyzed studies involving thousands of patients worldwide, have found a positive association between hypertension and glaucoma. Therefore, patients with hypertension should be assessed for glaucoma more diligently.