Astigmatism is a vision problem where objects at any distance can appear blurred. It is usually corrected with glasses or contact lenses. It is one of a set of vision problems referred to as “refractive errors”, and this collection of conditions includes nearsightedness (myopia), farsightedness (hyperopia) and the loss of close vision associated with age (presbyopia). Refractive errors are not a health problem, but simply affect the way that eyes focus light.
Diabetes is a disease where sugar is not effectively moved from the blood stream into the cells. Sugar is vital as a form of energy and normally enters the cells of muscle, fat and liver to be used for energy or stored as a reserve. The hormone insulin is required to transfer sugar from the blood into the cells, and patients with diabetes either do not produce insulin (type 1 diabetes), or have developed a resistance to its action (type 2 diabetes). Diabetic patients therefore have high levels of sugar in their blood. Both type 1 and type 2 diabetes list “blurred vision” as a symptom.
Diabetes is a complex disease, with symptoms which are wide-ranging and can be severe. Eye problems are well-documented and are referred to collectively as diabetic eye disease. Diabetic eye disease most commonly includes diabetic retinopathy, where the tiny blood vessels in the light-sensitive retina are damaged, but may also include cataracts and glaucoma. Astigmatism is not normally listed as a common component of diabetic eye disease, but is there a link?
To understand the nature of astigmatism, you should consider what causes it. Unlike other refractive errors of vision, astigmatism results in a blurred image of objects at any distance. It is normally due to a misshapen cornea at the front of the eye, or a misshapen lens. The typical analogy to describe the nature of an astigmatic cornea is to compare the shapes of a baseball and a rugby ball. The curvature of a baseball is the same across its surface because it’s spherical. That is a good design for a cornea or for each face of the convex lens. A rugby ball is longer in one axis than the other, and that is the case with the astigmatic eye. Some light is bent more than others as it passes through the misshapen cornea or lens, resulting in a fuzzy image.
How might this relate to diabetes? Glaucoma is one of the diabetic eye diseases, and the loss of vision is due to destruction of the optic nerve. This is due to an increase in pressure in the fluid in the front of the eye, in the anterior segment between the cornea and lens. This is known as ocular hypertension and is found in patients with diabetes. This increase in fluid pressure could account for the blurred vision reported as a symptom of type 1 and type 2 diabetes, even though some sources describe ocular hypertension as not affecting eyesight. Increasing the pressure on the cornea and the lens could result in deformation of the shape of those eye elements in some people, resulting in the typical blurred vision of astigmatism.
There are also reports of high blood sugar levels directly affecting the shape of the lens, though the mechanism for this is unclear. Astigmatic vision problems have been reported in patients before treatment for diabetes, and resolving (or reported as farsightedness) upon treatment. Clearly there is some link between high blood sugar levels and vision, but it is unclear if these changes can be called astigmatism in the traditional sense.
About the Author
Dr. David Cronauer works for ReplaceMyContacts.com, an online retailer of cheap contact lenses such as Acuvue Oasys and Proclear Toric. He is a graduate of Wilkes University Pennsylvania College of Optometry where he received his Doctor of Optometry degree. Dr. Cronauer is certified in the treatment and management of ocular disease and specializes in vision-related problems for head injury and stroke victims.