PREGNANCY AND GLAUCOMA

GUEST AUTHOR

SANIA KHAN

AJMAL KHAN TIBBIYA COLLEGE

ALIGARH, INDIA

INTRODUCTION

Although glaucoma is a disease of the older population, but it may sometimes affect women of childbearing age.

Glaucoma is rarely diagnosed during pregnancy; occasionally patients with preexisting glaucoma become pregnant, however.

Management of glaucoma during pregnancy is a challenge due to side effects and teratogenic effects of medications, as well as the risk of surgery on the mother and fetus has to be considered.

This post takes a look at the features of glaucoma during pregnancy and it's management.

IOP AND PREGNANCY

Intraocular pressure (IOP) is decreased by 10% in women during pregnancy with normal eyes.

In glaucomatous pregnant women with Ocular hypertension (OHT), there is significant decrease in IOP as compared to normal pregnant women without OHT.

IOP decline in non-glaucomatous pregnant women occurs between 12-18 weeks of pregnancy. While in women with OHT this decline occurs between 24-30 weeks.

The ocular hypotensive effect of late pregnancy is significantly greater in multigravidae than in primigravida due to an effect of the increased stress and discomfort felt by the primigravidae.

This stress can induce the release of large quantities of epinephrine and norepinephrine, leading to a higher IOP. However, the effect of psychological stress on IOP has never been proven.

The exact cause of lowered IOP during pregnancy in healthy women is unknown.

It is proposed that increased uveoscleral outflow due to changes in hormonal levels.

Estrogen, relaxin, progesterone and beta-chorionic gonadotropin are the suspect hormones.

Acidosis and decreased aqueous production are also proposed as a cause of lowered IOP but aqueous flow rate has been found to be consistent during pregnancy.

Decreased episcleral pressure during pregnancy is also proposed as the mechanism for lowered IOP.

IOP measurement errors due to reduced corneo-scleral rigidity, making tonometry readings falsely low, is another factor.

The physiologic changes of pregnancy are so numerous and complex that it is very difficult to reach any definite conclusion.

The highest drop of IOP in the third trimester of pregnancy was 2.7 mmHg as compared to non-pregnant women.

Reduced diurnal variation of IOP as well as lowered IOP in the third trimester have a protective effect in pregnant patients with glaucoma.

Pregnant women may avoid treatment of glaucoma to protect the fetus, thereby increasing non-compliance.

CORNEA AND PREGNANCY

A measurable, but slight increase in corneal thickness has been found in pregnant women.

The central corneal thickness was increased 16 microns (p=0.1) compared to the control eyes. This increase occurs due to water retention.

The lower IOP in pregnant patients did not correlate with corneal thickness.

VISUAL FIELDS IN PREGNANCY

The visual field changes during pregnancy include bitemporal contraction, concentric contraction and enlargement of the blind spot.

Proposed mechanisms for these visual field changes are diverse.

MRI studies show that the size of pituitary gland is increased about 120% during a normal pregnancy, so it is believed that the pituitary impinges on the optic chiasm causing the temporal hemifield deficit, the most common visual field defect in glaucoma is in the nasal hemifield.

The rarity of glaucomatous visual field defect in the temporal visual field and reversibility of any kind of VF defect after pregnancy are important features to distinguish between glaucomatous and pregnancy induced VF defects.

RETROBULBAR BLOOD FLOW IN PREGNANCY

Altered retrobulbar blood flow plays an important role in the pathogenesis of open angle glaucoma.

Vascular dysregulation in susceptible patients, independent of atherosclerosis is thought to reduce ocular blood flow.

Alterations in hormonal status leading to changes in CVS are also implicated.

The influence of menopause and post menopausal hormone supplementation on the incidence of coronary artery disease in women has been explained in various studies and this seems to be linked to the "estrogen vasodilator activity".

Blood flow velocities in the retrobulbar arteries are significantly increased by estradiol.

Ocular Blood Flow changes may occur due to physiologic and progressive increase of estrogen secretion during pregnancy.

There may be significant increase in pulse ocular blood flow in pregnant women as compared to non-pregnant women.

The pulse Ocular Blood Flow is 500 ml/min in the first quarter of pregnancy and 600 ml/min in the second quarter greater than in non-pregnant women.

Resistive index and pulsality index are inversely proportional to the gestational age.

During pregnancy there is an increase in estrogen that induces endothelial-dependent vasodilation in several tissues and maybe cause of increased ocular blood flow.

Intranasal administration of 17-beta estradiol increased the peak systolic and end diastolic velocities of the Central retinal artery without any significant difference in ophthalmic artery flow velocities or pulsality and resistive indices.

Glaucomatous and non-glaucomatous postmenopausal women who received hormone therapy may show a significant decrease in ophthalmic artery pulsatile index.

The Ophthalmic artery mean pulsality index decreases significantly more in non-glaucomatous women than in glaucomatous women (-43% vs. 28%; p=0.001).

Patients with lower retinal blood flow velocities may show higher rates of progression of glaucomatous damage.

In some women with increased retrobulbar blood flow and lower IOP during pregnancy, the protective effect of pregnancy on glaucoma progression is possible.

LABOR IN GLAUCOMATOUS PATIENTS

Angle-closure glaucoma may be precipitated during labor in women with narrow angles.

The mean IOP increased by 1.4 mmHg during the course of labor then decreased by 3.0 mmHg immediately after delivery. The IOP returned to pre-labor levels in all patients by 72 hours after delivery.

Oxytocin levels increase during labor which leads to capillary constriction and decrease in aqueous outflow but there is no evidence linking oxytocin to IOP.

Valsalva maneuvers also increase IOP during labor but their effect on progression of glaucoma is not proven.

Some studies found a higher risk for glaucoma progression in patients with low blood pressure. Transient hypotensive shock may also lead to glaucoma-like optic nerve and VF changes.

Large amount of blood loss during labor leads to transient hypotension and increased risk for glaucoma progression.