Introduction
Preeclampsia is a multisystemic disorder of pregnancy characterised by abnormal vascular response to placentation with increased systemic vascular resistance, a hypercoagulable state and endothelial dysfunction.1 2 Preeclampsia is defined as elevated blood pressure >140/90 mm Hg taken on two consecutive occasions at least 6 hours apart and the presence of proteinuria after a gestational age of 20 weeks in a previously normotensive and non-proteinuric woman that resolves 6 weeks postpartum.1 2 Preeclampsia before 32 weeks is said to be early-onset and is associated with increased morbidity.1 2 The prevalence of preeclampsia is about 5% to 10% of all pregnancies, especially frequent in primigravid women.1–4 Risk factors for preeclampsia include primigravidity, family history of preeclampsia, chronic renal disease, chronic hypertension, preceding history of preeclampsia, high body mass index or obesity, antiphospholipid syndrome, diabetes mellitus, extremes of age (<18 or >40), black race, twin gestation and presence of angiotensinogen gene.1 2 However, the exact cause of preeclampsia is unknown.1 2
Preeclampsia can present with complications in the eye in 30% to 100% of patients.5 Specifically, visual disturbance develops in 25% of women with severe preeclampsia, but blindness is rare and occurs at an incidence of 1% to 3% in eclampsia.5 Visual symptoms in preeclampsia and eclampsia include: photopsia, visual field defects, sudden inability to focus, blurred or decreased vision and, in severe cases, complete blindness.5–7
The severity of the ocular changes observed depends on the severity of preeclampsia.5 8 Retinal changes are likely to occur when diastolic blood pressure is more than 100 mm Hg and systolic blood pressure more than 150 mm Hg.7 9 The three most common ocular complications are hypertensive retinopathy, exudative retinal detachment and cortical blindness.7 8
Hypertensive retinopathy, the most common manifestation of preeclampsia and eclampsia occurring in 60% of patients, clinically evaluated by funduscopy, may be associated with oedema, haemorrhages, exudates and cotton wool spots, leading to a decrease in the retinal artery to vein ratio.10 11
Another primary pathology in preeclampsia patients is retinal detachment, which may be localised but without rapid treatment may involve the entire retina, leading to loss of vision and blindness.7 12 13 It has been shown that preeclamptic women complicated by HELLP (Haemolysis, Elevated Liver enzymes and Low Platelets) syndrome are seven times more likely to develop retinal detachment than those who do not develop HELLP.14
Furthermore, retinal pigment epithelium lesions called Elschnig spots may also occur in preeclamptic patients with choroidal infarcts.15 Cortical blindness occurs in up to 15% of patients with preeclampsia and eclampsia from petechial haemorrhages and focal oedema in the occipital cortex.8 16 Symptoms of headache, hyperreflexia and paresis may precede or be accompanied by cortical blindness.8 17 Cerebral blood flow velocity is increased in pregnancy-induced hypertension, suggesting an increased resistance to flow.18 Doppler studies of the orbital vessels give information on intracranial circulation due to the similarities in the embryology, anatomy, and function of orbital and intracranial vessels.18–20
Ocular ultrasonography has become an essential tool in the evaluation of ocular diseases.21 While the B-mode ultrasound evaluates the anterior chamber and posterior segment, including the anchored retinal layer, the Doppler ultrasound mode evaluates blood flow in blood vessels in the eye.19–21 Doppler ultrasonography detects changes in ocular blood flow resulting from changes in mean arterial blood pressure at the level of the eye and changes in intraocular pressure.19 21 Also, ocular Doppler is an accurate and objective method of evaluating preeclampsia severity.19–22
There is a paucity of literature comparing the ocular changes among preeclamptic and normotensive pregnant Nigerian women.22 This study compared the ocular changes in preeclamptic women with normotensive pregnant women to determine if there is a difference in the visual acuity, intraocular pressure, ophthalmoscopy findings and ophthalmic Doppler velocimetric findings between the two groups. In addition, this study also evaluated whether the ocular changes seen in preeclamptic women correlated with the severity of the disease.