The full list of systemic diseases associated with signs in the eye is one that is too long to be contained in a single post. It ranges from the obscure syndromes such as Marfan’s and Vogt-Koyanagi-Harada (that would be a mouthful to say) to the more well-known conditions of diabetes and hypertension. Don’t forget, the same blood that runs through your liver and down through the blood vessels of your toes eventually also circulates through your eyeballs.

The role of an eyecare practitioner is sometimes akin to that of a detective – picking up various little clues during an eye examination that could result in making a deduction about your cholesterol levels or the presence of a certain gene in your DNA, perhaps even making a link to your ongoing bowel problems or mouth ulcers.

Anterior Eye Clues

The anterior eye is the part that’s visible to you in the mirror. It includes the sclera (the whites of the eyes), the cornea (the transparent dome over the coloured part of the eye), and the iris (the coloured part of the eye). It also includes the space between the cornea and the iris, known as the anterior chamber.

Iritis or anterior uveitis is not an uncommon condition involving an inflammatory event in the anterior chamber of the eye. In many cases there is no known reason for this happening, which is then given the term idiopathic but in other situations, particularly those involving recurrent iritis, it may herald another seemingly unrelated disease. About 50% of recurrent anterior uveitis cases are associated with a gene called HLA-B27. This gene has also been linked to a number of autoimmune diseases, which are subsequently considered to be associated with iritis – ankylosing spondylitis (inflammatory back pain, particularly worse in the mornings and improving with physical activity), Crohn’s disease and ulcerative colitis (inflammatory bowel diseases), psoriatic and juvenile idiopathic arthritis, and Behcet’s disease (involving mouth ulcers).

The cornea can also be witness when it comes to systemic disease. Usually a transparent anatomical structure, the cornea is an important component of the optical system of the eye. Corneal arcus results from lipid/cholesterol deposition and can be seen as a whitish-greyish-bluish ring around the periphery of the cornea. It is fairly common in older adults, approaching 100% prevalence in patients over 80 years of age and typically doesn’t indicate an issue with blood cholesterol levels. However, in younger adults under 40 years of age, it may be evidence of hyperlipidemia (high cholesterol) and coronary artery disease.

Kayser-Fleischer rings are a greenish-brownish haze of the peripheral cornea and are considered the single most important diagnostic sign of Wilson disease. Wilson disease involves abnormal copper metabolism; the Kayser-Fleischer ring is a result of copper deposition in the cornea.

It’s not difficult to deduce what systemic condition is associated with thyroid eye disease – you guessed it, Graves’ disease! (or perhaps that one was a little harder to guess). Ocular manifestations of hyperthyroidism (Graves’ disease) often begin with proptosis, which is the medical term to describe the eyeballs popping outwards from the sockets as the inflamed and enlarged eye muscles behind it begin to push the eyeball out. Don’t worry, the eyeballs don’t actually pop right out of their sockets, but this state of proptosis in itself can cause issues such as corneal dryness and ulceration as the eyelids are not able to blink fully over the eye. The enlargement of the eye muscles can also result in a restriction of eye movements and subsequent double vision in certain directions.

Posterior Eye Clues

The posterior eye refers to the retina, which is the light-sensing tissue at the back of the eye. The retina is a special piece of anatomy as it is the only area of the body where blood vessels can be seen in vivo, live in action, and quite often the state of these retinal blood vessels provide clues about the rest of the body.

Retinal hemorrhages can be evidence of several different systemic diseases. While in many cases a retinal bleed may be idiopathic it can also point to the presence of diabetes or hypertension. Both of these conditions result in damage to blood vessel walls throughout the body and can sometimes present a hemorrhage large enough to obscure the vision. In most cases the bleed is quite small and the patient may not even realize there’s a problem in the eye; sometimes they don’t even realize they have any health problem at all, and the first indication of a disease like hypertension is only picked up during an incidental eye exam. Other retinal signs of diabetes or hypertension include microaneurysms, swelling between the layers of the retina, fluffy-looking patches indicating loss of oxygen supply, and subtle changes to the appearance of the blood vessels themselves.

The swelling of the optic nerve head in the retina is termed papilledema. Though this is another presentation that could have an idiopathic cause, the other potential differential diagnoses are too serious to not investigate thoroughly. Papilledema is a sign of increased pressure inside the skull (intracranial pressure), which pushes against the optic nerve in the eye, causing it to swell and bulge. Raised intracranial pressure may be due to a brain tumour or hemorrhage, a blockage in the drainage channels of the brain, or a brain infection resulting in decreased absorption or cerebrospinal fluid. Often the first clue to raised intracranial pressure might be reports of a persistent headache.

As you can see, the eye can be a bit of a snitch when it comes to the systemic health of the body; if ever it were to take the witness stand it would have a lot to say. Sometimes it might know something’s up even before other parts of your body do.

References
Eye in Systemic Disease. https://patient.info/doctor/eye-in-systemic-disease

The Uveitis and HLA-B27 Connection. https://www.reviewofoptometry.com/article/the-uveitis-and-hlab27-connection

Corneal arcus. https://www.aao.org/bcscsnippetdetail.aspx?id=75f705e5-3ebe-4593-837d-5ae7bc3d44f3

Ocular signs in Wilson disease. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3424798/

Dense Kayser-Fleischer ring in asymptomatic Wilson’s disease (hepatolenticular degeneration). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1770985/

Papilledema. http://eyewiki.aao.org/Papilledema