Through your eyes you see out into your environment and gather information about your surroundings. The same is true of the reverse; that is to say, your doctor can use a vision test to examine and assess your internal physical health. Visual acuity can be assessed using a standard eye exam and are often part of a routine primary care visit. The eye is a window into your body, allowing the examiner to assess your risk for systemic disease such as high blood pressure and diabetes.
The Retina
In the back of your eye lays a highly specialized sensory system known as the retina. Composed of millions of cells capable of detecting single photons of light, the retina is a highly metabolically active tissue requiring large amounts of energy to function properly. Ultimately, this means that this tissue depends on a constant, reliable source of oxygen and nutrients, which are supplied by a permeating bed of capillaries, or microscopic blood vessels.
The Effects of Vascular Disease
Because of the dense collection of capillaries within the retina, diseases effecting blood vessels, also known as vascular diseases, will commonly present themselves with vision problems. Upon further inspection, changes in the vasculature of the retina are often observed using the technique of fundoscopy, an examination your doctor performs with a hand held magnifying device. Depending on the particular disease process, this exam may reveal microscopic hemorrhages or aneurysms throughout the retina.
Diabetes
Diabetics have problems controlling the amount of glucose in their blood. A highly reactive molecule, glucose is capable of binding to various structures throughout the body, including small capillary vessels. Overtime, chronically elevated glucose levels will damage these microscopic blood vessels, leading to the development of vascular disease. When the capillaries within the retina are affected, the result is a condition known as diabetic retinopathy. Characterized by blurred vision, poor vision at night, appearance of spots or floating strings, and vision loss, retinopathy is a serious complication of diabetes that can be detected early with a vision test.
Hypertension
Chronic high blood pressure can cause similar damage to capillary beds throughout the body and may be observed in the vasculature of the retina. These small blood vessels develop thick walls when under constant pressure; these changes make it difficult for blood to properly flow through them. This may result in inadequate blood supply to the sensory cells of the retina, leading to cell death and retinopathy. As the condition progresses, hemorrhages may occur, causing blood to leak into the retina further compromising vision. If your vision test results are poor, your doctor will use an ophthalmoscope to look into your eye and examine the retina for this type of damage. Hypertension is a systemic condition that not only affects the vasculature of the retina, but also the heart, kidneys, and brain; recognizing that the disease has progressed to the point of damaging small vessels is an important indicator that your blood pressure requires more aggressive management.
AIDS
Another health problem that may affect a vision test is AIDS, or Aquired Immunodeficiency Syndrome. When white blood cell counts drop to a significantly low number, retinal hemorrhages begin to appear on the back of the eye. These changes may be experienced as vision loss as they begin to involve the optic nerve and fovea, or the portion of the retina most sensitive to light.
References
- Current Medical Diagnosis and Treatment: Disorders of the Eyes and Lids; Paul Riordan-Eva; 2010
- Merck Manuals: Hypertensive Retinopathy
