One of the most common questions I get is what is astigmatism and how did I develop it? Let’s dig deeper into the problem.
The eye exam
There are two main components to an eye exam. The first is a comprehensive eye health assessment; the second is to measure eye focus and prescribe appropriate glasses or contact lenses.
The eyes are examined for conditions such as cataracts, glaucoma, macular degeneration, retinal detachment and any other disease.
Next, an autorefractor is used to measure how the eye focuses light. During the test, you look inside the autorefractor at a target, such as a balloon or a barn. The autorefractor shines light into your eye as you look at the target and measures how the light is reflected back to the instrument. This autorefractor gives us a better estimate of the focus of your eyes.
The second part of measuring eye focus is when looking through the refractor. The refractor is the instrument through which you look and you are asked to answer the question: “Which lens makes the letters clearer, lens one or lens two?” This process in which we measure how the eyes focus is called refraction.
Refraction has two parts. The first measures how the eyes focus things at a distance and the second measures how the eyes focus things close (16 inches away). During refraction, we determine if someone has nearsightedness, farsightedness, astigmatism, or a combination.
Nearsightedness is commonly referred to as nearsightedness. It’s when you see better up close and less well from afar. The higher a person’s myopic prescription, the worse their distance vision. For example, someone with -5.00 diopters of myopia will have a much harder time seeing in the distance than someone with -1.00 diopters of myopia. Hyperopia, commonly known as farsightedness, occurs when a person’s near vision is worse than their distance vision. This should not be confused with a refractive error called presbyopia. The higher a person’s farsightedness prescription, the worse their near vision.
For example, someone with +5.00 diopters of farsightedness will have much more difficulty seeing up close than someone with +1.00 diopters of farsightedness. Often, these people will be increasingly dependent on their glasses to improve their distance and near vision.
Astigmatism is a refractive error in which light entering the eye focuses on two different meridians. People with astigmatism actually have a different prescription for going up and down in their glasses than going left and right. Each line in the lens represents a different power. Although the lines in the figure represent different powers in the lens, there are no visible lines in the lens.
Astigmatism often causes distance and near vision to be blurred if left uncorrected. The higher a person’s level of uncorrected astigmatism, the more it will affect their vision. If you have astigmatism correction in a pair of glasses for the first time, or if you have an increase in the amount of astigmatism, your glasses may feel awkward when you first put them on. Vision will often seem clear, but they may feel like things are being magnified or minimized, it may seem like the floor is tilting towards you or towards you, it may seem like doors are tilted or you may have the impression of reaching things that are not exactly where one would expect them to be.
The reason for the potentially awkward sensation with the astigmatism prescription is that when you have two different powers in your glasses, they have different magnification levels in each meridian. Anytime these powers are changed, they can affect how you view the world through the glasses.
The good news is that simply wearing glasses and performing daily tasks in the glasses will help you get used to the new prescription. It’s important not to just sit and watch TV or stare at a computer screen with your new prescription on, but be sure to get outside and do active tasks with glasses.
There are two forms of astigmatism: regular and irregular. Regular is the form of astigmatism that most people have. It is there that the two different powers of which we spoke previously are located at 90° from each other. Irregular astigmatism occurs in certain conditions where the astigmatism is not located 90° apart.
Some examples of conditions that can cause irregular astigmatism include keratoconus, corneal damage, and epithelial basement membrane dystrophy. Presbyopia Presbyopia is where individuals in their early 40s lose the ability to focus on things up close. This happens because the lens inside the eye loses its elasticity over time. As the lens loses its elasticity and hardens, it has less ability to focus things that are closer to the eye. This is part of the reason why the primary compensatory mechanism for presbyopia is to move objects away from your face to help see it clearly. Presbyopia will get worse once someone starts experiencing symptoms. This is the reason why the near power of the glasses or the bifocal power of your glasses should be increased until it stabilizes around age 60.
Back to astigmatism
Astigmatism is when there are different power requirements in two different meridians.
There are good ways to correct it with glasses, contact lenses or, for some people, a wetsuit. It is not very uncommon for astigmatism to change over time.
Remember that this is simply a different way your eye focuses light and not a medical condition.
Mile Brujic, OD, FAAO graduated in 2002 from the New England College of Optometry. He is a partner of Premier Vision Group, an optometric practice with three locations in northwest Ohio. He practices comprehensive optometry with an emphasis on the management of anterior segment ocular disease and specialty contact lenses. Brujic is a member of the editorial board of several optometric publications. He has published over 350 articles and given over 1,600 lectures, both nationally and internationally, on contemporary eye care topics.