What an eye exam can determine about your health
The eye has been termed the window to a person’s soul. It is a unique organ and is composed of many different types of tissue. This unique feature makes the eye susceptible to a wide variety of diseases as well as provides insights into many body systems. Different parts of the eye may be involved in various systemic diseases and these can give important clues to the diagnosis of systemic diseases. These signs of disease may be found on the outer surface of the eye (eyelids, conjunctiva and cornea), middle of the eye and at the back of the eye (retina).
What makes the eye unique from other parts of the body is that certain eye structures are transparent. This includes the cornea (the clear circular window in the front of the eye), the lens (the structure involved in focusing), and the vitreous (the gel-like structure that fills the back chamber of the eye). This property enables the eye doctor to see inside the eye and is the only organ in the body in which an eye doctor can directly see the blood vessels. The health of the blood vessels in the eye often indicates the condition of the blood vessels (arteries and veins) throughout the body. In addition, we are able to see the optic nerve, which is part of the central nervous system, and really is an extension of the brain, and so features seen in the optic nerve may give us a clue to abnormalities in the brain.
Diseases that can affect the eye
Many systemic diseases have eye manifestations. These diseases affect the eye differently. Sometimes, the eye findings may be the first indication of underlying systemic diseases.
Thyroid disease
Thyroid disease can cause eye changes. A common thyroid disease is known as Graves’ disease, which is associated with an enlarged thyroid gland in the neck, features of hyperthyroidism due to elevated thyroid hormones (such as a fast heart rate, weight loss, sweaty palms, tremors) and eye manifestations. The eye features include an increase in the upper lid position (lid retraction), protruding eyes (proptosis), a staring appearance, limitations of eye movement due to eye muscle involvement which can lead to double vision, inflammation of the orbital and eye tissues, and corneal damage from over-exposure of the cornea due to poor lid closure. Severe cases may result in significant orbital inflammation that can be severe enough to compress and damage the optic nerve and result in loss of vision. Sometimes, the eye symptoms in Graves’ disease can appear before other systemic symptoms and signs. Management of the thyroid disease can help to reduce the severity of the eye changes.
Diabetes mellitus
Diabetes mellitus is major cause of blindness in developed countries including Singapore. It can affect the eyes in many ways. Diabetes affects the small, medium and large vessels of the body. A common complication is diabetic retinopathy (DR) where the small vessels of the retina (nerve layer) are affected.
The incidence of DR increases with the duration of diabetes, and those with more than 10 years of diabetes have a high chance of developing some degree of blood vessel abnormalities and retinopathy. In fact, 99% of people with type 1 diabetes and 60% of those with type 2 diabetes will develop some form of retinopathy within 20 years of disease onset. People with insulin dependent diabetes and who have suboptimal diabetic control are more likely to develop complications.
In the early stage of diabetic retinopathy, there are tiny bleeding spots, small microvascular changes (microaneurysms), increased vascular permeability and leakage of proteins and fat (exudates). This may occur in any part of the retina. In this early stage, known as non-proliferative DR (NPDR), the individual may not notice any visual symptoms. As the disease progresses, new abnormal vessels may develop (neovascularisation) on the surface of the retina or the optic nerve, known as proliferative DR (PDR). These immature new vessels may rupture and bleed into the eye (vitreous haemorrhage) and cause a sudden loss of vision. There may also be scarring and fibrosis around the vessels and optic nerve which may cause traction and pull on the retina, resulting in retinal detachment and loss of vision.
The fluid leakage into the area of the retina which is responsible for clear central vision (macula) is called diabetic macular edema (DME). Today, about 11% of those with diabetes have DME, and 1 to 3% actually suffer from loss of vision because of DME.
Apart from retinal involvement, those with diabetes tend to develop cataracts earlier. Retinopathy can precede nephropathy, making the early detection of ocular manifestations of diabetes essential.
Treatment of DR include laser treatment to stabilise the eye condition, injection of antivascular proliferative factors (anti-VEGF) to reduce swelling of the retina, and in the severe stage, surgery may be required. Therefore, it is important for those with diabetes to have regular eye checks and have good blood sugar control to prevent and control the progression of DR.
Hypertension
Hypertension remains a significant cause of morbidity and a leading cause of cardiovascular mortality. Hypertension affects the eye in a multitude of ways, including vascular injury and increased risk of embolic events (eg retinal vein and retinal artery occlusion).
Hypertension can affect the retinal vessels, leading acute and chronic retinal changes, known as hypertensive retinopathy. These changes include retinal haemorrhages, capillary obliteration, swelling of the optic nerve and retina (macular edema), and shunt vessels. Hypertension can also indirectly cause more serious complications like strokes to the retinal vessels (retinal vein occlusion, retinal artery occlusion), strokes to the optic nerve (ischaemic optic neuropathy) and macroaneurysms.
Hypertensive retinopathy is considered a prognostic indicator of systemic disease. Perhaps the strongest correlation is between hypertensive retinopathy and risk of stroke. A study revealed that hypertensive retinopathy increased stroke risk twofold to fourfold when those with this condition were compared with those who had no retinopathy. Studies also suggest that hypertensive retinopathy can be used to predict the risk of congestive heart failure, left ventricular hypertrophy and renal impairment.
Inflammatory conditions
Many inflammatory conditions of the body can involve the eye. Sometimes, the eye features are the first clue to an individual having an underlying systemic inflammatory condition. Management of these conditions involve treating the underlying systemic disease as well as the associated eye complications.
- Systemic lupus erythematosus and rheumatoid arthritis
Up to 25% to 33% of those with systemic lupus erythematosus and rheumatoid arthritis have eye conditions. They can cause inflammation of different parts of the eye, such as episcleritis (superficial inflammation of the sclera), scleritis (deeper inflammation of the sclera), keratitis (inflammation of the cornea). It can also cause inflammation of the inner cavity of the eye, known as uveitis or iritis.Inflammation of the eye presents with painful and red eyes, blurred vision and glaucoma (rise in eye pressure). These conditions can also cause dry eye. Those with scleritis are associated with more widespread and severe RA, with a higher mortality rate. These can also affect the vessels and retina, resulting in features that are similar to hypertensive retinopathy and retinal inflammation.
- Ankylosing spondylitis
This is an inflammatory condition that mainly affects the spine, and can be associated with internal inflammation of the eye (anterior uveitis). Those with this condition present with a painful red eye associated with loss of vision.
- Inflammatory bowel disease
Ulcerative colitis and Crohns disease which are relapsing inflammatory diseases involving the gastrointestinal tract, may be associated with inflammation of the eye, including uveitis, episcleritis and scleritis.
Treatment of inflammatory conditions involving the outer and internal structures of the eye involve the use of topical steroid medication in the form of eyedrops and ointments. In more severe conditions, injections of steroids around the eye or oral steroids may be used to control the inflammation.
HIV and AIDS
HIV and AIDS can cause various eye complications. HIV infection places those with it at risk for both infectious and non-infectious complications. The ocular manifestations of opportunistic infections are categorised based on anatomical origin (orbital/adnexal manifestations [external] versus anterior/posterior segment manifestations [internal]) or non-specific systemic infection. Infections around the lids include molluscum contagiosum and herpes zoster ophthalmicus.
The first sign of AIDS may be abnormalities in the retina. Thirty percent to 50% of those with AIDS may develop posterior segment manifestations, with the most common abnormalities being attributable to cytomegalovirus infection and retinal microvasculopathy.
AIDS can also cause retinal detachment, eyelid tumours and neuro-ophthalmic disorders. Systemic infections such as cryptococcal meningitis or toxoplasmosis can have ophthalmic involvement and visual-field loss. AIDS-related infections can often lead to blindness, but effective eye treatment is now available.
Atherosclerotic diseases
Atherosclerotic disease and carotid artery stenosis may cause plaques in the retinal arterioles which may be picked up incidentally on routine eye screening. More severe complications of atherosclerotic disease include retinal vessel occlusion (eg retinal arterial or retinal vein occlusions) or neovascular glaucoma, which is a form of glaucoma that is very difficult to treat. The eye manifestations may be the first sign of more serious underlying cardiovascular disease.
Metastatic cancers
The eyes are a possible site of metastatic spread of tumours from other parts of the body. The most common primary tumours are the lung and breast. Individuals may be asymptomatic, or may complain of decreased or distorted vision if the retina is involved, or a red and painful eye if there is an inflammatory reaction to the tumour cells. Sometimes, a mass is detected in the posterior segment incidentally and this may be the first sign of cancer.
Summary
Those with ocular manifestations may first present to the emergency department with relatively non-specific symptoms such as visual disturbance or eye pain. In some cases, however, the information obtained from an ocular examination may aid in the differential diagnosis and appropriate management of the underlying disease.
A thorough eye examination is therefore important, as it may provide valuable information regarding other parts of the body. The eye may be involved as part of the complications of a disease, or the eye may be the first sign of the disease. The fundoscopic examination can enable us to have a direct view of the microvessels of the eye, which in turn may be a clue to predict underlying systemic disease (such as cardiovascular diseases, hypertension, diabetes), as well as its severity. Therefore, it is prudent for anyone above 45 years of age to go for a detailed eye examination with an eye specialist, so that these diseases may be detected and treated early.
