Abstract
The tear film consists of three layers: the outer lipid layer, the middle aqueous layer and the inner mucin layer. The stability of the tear film is dependent on all three layers functioning in an optimal, synergistic manner. The lipid layer is secreted by the Meibomian glands and the aqueous and the mucin layers by the lacrimal glands and goblet cells, respectively.
In pregnancy, the tear film becomes unstable and alters in composition, causing it to break up quickly, resulting in irritation and discomfort to the patient (Figure 25.1). It is important to examine the eye under a slit lamp and exclude any other lid or corneal pathology, which could be contributing to these ocular symptoms.
Key Facts
The ocular conditions in pregnancy can be broadly subdivided into three main categories:
Changes seen secondary to normal physiological changes observed during pregnancy [1]
Changes due to pathological conditions – both pregnancy-specific and non-specific
Changes due to preexisting ocular disease or its altered course during pregnancy
Visual Symptoms Due to Physiological Changes of Pregnancy
Tear Film Changes
The tear film consists of three layers: the outer lipid layer, the middle aqueous layer and the inner mucin layer. The stability of the tear film is dependent on all three layers functioning in an optimal, synergistic manner. The lipid layer is secreted by the Meibomian glands and the aqueous and the mucin layers by the lacrimal glands and goblet cells, respectively.
In pregnancy, the tear film becomes unstable and alters in composition, causing it to break up quickly, resulting in irritation and discomfort to the patient (Figure 25.1). It is important to examine the eye under a slit lamp and exclude any other lid or corneal pathology, which could be contributing to these ocular symptoms.
Management
If no other disease process to explain ocular irritation is found, the patient can be reassured. Initially, simple steps can be tried such as ocular hygiene (use of cotton buds and warm water to clean the upper and lower eyelids to remove any dust) and creation of a more humid atmosphere at work or at home. The latter may include use of a humidifier and practical steps such as opening windows, having plants on the desk or around the home and keeping them watered. Smoke also irritates the eyes and patients should be advised to avoid smoking during pregnancy. When outdoors, ‘wrap-around’ sunglasses may help. Massaging the eyelids gently may encourage mucus to be pushed out of goblet cells.
Despite these measures, if the symptoms are troublesome and are affecting everyday activities, then preservative-free lubricants could be prescribed to alleviate discomfort and irritation.
Corneal Changes
The cornea is the transparent structure located on the front of the eyeball that is important for clarity of vision. It consists of the following five layers:
Stratified squamous non-keratinised epithelium
Bowman’s membrane, which is acellular
Stroma consisting of regularly arranged collagen fibres with a ground substance of proteoglycans
Descemet’s membrane of thin collagen fibres
Single-layered endothelium
The thickness of the cornea changes during pregnancy, and this could affect the clarity of vision. Changes in the shape and size of the eyeball secondary to physiological fluid retention and changes in blood pressure during pregnancy may result in minor changes in the refractive power of the eyes. In addition, contact lens wearers may feel they are intolerant of contact lenses during pregnancy and may find them ‘ill-fitting’.
Management
It is important to exclude any other ocular pathology that may cause changes in vision by careful anterior and posterior segment examination. A refraction test may show slight changes in the power compared with the previous examination. If pathological causes have been excluded, the changes observed in vision should be explained to the patient and she should be reassured that these changes will subside following pregnancy and she need not change the prescription of her glasses or contact lenses [2]. However, contact lens wearers should be advised that if irritation and ‘ill-fitting’ contact lenses due to changes in the shape of the eyeball are a problem, changing to glasses during pregnancy may improve their symptoms.
Patients contemplating corneal surgery should be advised that the corneal thickness is variable during pregnancy and may affect the final outcome. Hence, corneal surgery should be recommended 3 months after birth.
Visual Symptoms Due to Pathological Conditions During Pregnancy
Blurring of vision and sudden loss of vision may occur due to pregnancy-specific pathological conditions as well as primary ocular or ocular manifestations of underlying systemic disorders that occur de novo during pregnancy.
Pregnancy-Specific Disorders: Severe Preeclampsia and Eclampsia
Severe preeclampsia and eclampsia are potentially life-threatening conditions that are specific to the pregnant state. Although the exact aetiology is unknown, they are believed to be due to the widespread endothelial damage secondary to abnormal placentation and subsequent release of vasoactive factors. These result in systemic vasospasm, endothelial cellular damage (endotheliosis) and activation of the coagulation system resulting in disseminated intravascular coagulation. The diagnostic criteria for preeclampsia include blood pressure of >140/90 mm Hg in a pregnant woman after 20 weeks’ gestation with proteinuria >300 mg/24 hours. However, severe preeclampsia is diagnosed when the systolic blood pressure rises above 160 mm Hg and/or the diastolic blood pressure rises above 110 mm Hg with or without visual, hepatic or neurological symptoms. Onset of seizures is referred to as eclampsia.
Preeclampsia is common in primigravidas and has an incidence of about 5%. Women with underlying chronic hypertension and renal disorders are at increased risk of developing ‘superimposed’ preeclampsia during pregnancy. In addition, women with underlying immunological disorders (e.g. systemic lupus erythematosus [SLE]) and thrombophilia (congenital and acquired) are also at increased risk of developing preeclampsia.
Visual symptoms include blurred vision, double vision and photopsia, which are often associated with headaches and epigastric or right hypochondrial pain (hepatic involvement). Ocular manifestations of preeclampsia include features of optic neuropathy, which include papilloedema, optic neuropathy and optic atrophy.
On examination, visual acuity may be reduced depending on the severity and the location of the disease process within the eye. Retinopathy seen in preeclampsia is similar to hypertensive changes and is characterised by nerve fibre layer infarcts, hard exudates, flame-shaped haemorrhages, retinal oedema and narrowing of arterioles.
Swelling of the optic nerve head is a hallmark of malignant hypertension. Choroidal changes are less common in preeclampsia and would lead to Elschnig’s spots, which represent focal choroidal infarcts. There may also be bilateral exudative retinal detachments.
There is a correlation between the severity of preeclampsia and the extent of retinal involvement. Retinal changes are more marked in patients who have pre-existing conditions such as renal disease and long- standing diabetes mellitus.
In preeclampsia, serous retinal detachments may also occur due to choroidal non-perfusion and subretinal leaks. These usually present as bilateral bullous detachments and resolve in the postpartum period.
Rarely, occipital infarcts and visual loss due possibly to cerebral oedema may occur in severe preeclampsia and these often resolve with the control of preeclampsia.
History of sudden onset of blurred vision should be taken very seriously and preeclampsia needs to be excluded in all pregnant women. Ocular symptoms improve with treatment of hypertension and usually resolve after birth. Excluding any other coexisting pathology is paramount.
Rarely, thrombotic thrombocytopenic purpura (TTP) may be confused with severe preeclampsia with HELLP (Haemolysis, Elevated Liver enzymes and Low Platelets) syndrome. Clinical presentation in TTP includes thrombosis of small vessels leading to thrombocytopenia, microangiopathic haemolytic anaemia associated with neurological and renal dysfunction. Patients are often febrile. Ocular manifestations in TTP occur due to narrowing of retinal artery, serous retinal detachment, retinal haemorrhage and oedema of the optic disc. Rarely, patients may complain of homonymous hemianopia.
Pregnancy ‘Non-specific’ Disorders (Primary Ocular or Systemic Illnesses): Benign Intracranial Hypertension
Benign intracranial hypertension refers to the presence of raised intracranial pressure in the absence of an intracranial mass or hydrocephalus. This condition is usually common in obese females in the third trimester but may occur throughout pregnancy.
Benign intracranial hypertension may cause sudden loss of vision and may occur due to papilloedema. Other associated symptoms include headaches, which are worse with postural changes and straining, transient visual obscuration lasting a few seconds and nausea and vomiting. Some patients may have drowsiness and horizontal diplopia.
On examination of the fundus, in the early stages, hyperaemia and mild disc swelling may be seen. Once papilloedema is established, visual acuity may be normal or reduced and the optic disc margins may appear indistinct. Appearance of venous engorgement, para-papillary flame-shaped haemorrhages and cotton wool spots as well as hard exudate around the macular forms, macular fan and the enlargement of the blind spot are the associated ocular signs.
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