Search

Astigmatism

Last updated date: 25-Feb-2022

CloudHospital

15 mins read

Astigmatism - overview

Astigmatism

Astigmatism is an eye condition that affects the curvature of the cornea or the lens, causing blurred vision. It is a quite common condition and it can co-occur with myopia (nearsightedness) or hyperopia (farsightedness). Typically, astigmatism is present ever since birth, but it’s only diagnosed later in life since kids don’t usually realize the vision impairment. While sometimes it’s not a serious condition, if it becomes pronounced lenses or surgery can help with the symptoms.

First, let’s briefly tackle the anatomy of the eye and how it works in order to better understand what astigmatism is and what are its consequences.

 

The eyes – anatomy and function

The eye is the organ responsible for our vision, more precisely for receiving the light rays and getting all the information from the outside world into the brain where images are formed. The eye has some components, all of which are quite essential in their own way in the process of vision:

  • cornea – the exterior “window” of the eye that helps focus the light into the eye;
  • iris and pupil – the iris is the colored ring in the eye that has in the middle the pupil, a black circle; the muscles of the iris either dilate or constrict the pupil in order to make sure the eye gets the exact amount of light it needs;
  • lens – this is a transparent component, much like cornea, that is responsible for the way the light focuses on the retina in the back of the eye; the lens and the cornea are essential for a clear vision, both of them striving to focus the light properly;
  • retina – is a light-sensitive nervous tissue in the back of the eye; the retina senses the light stimuli that are focused by the cornea and the lens and it creates electrical impulses that reach the brain through the optic nerve;
  • macula – is the central zone in the retina that has special cells responsible for allowing us to see clearly fine details;
  • peripheral retina – the outer parts of the retina, responsible for our side (peripheral) vision;
  • photoreceptors – the special cells that convert the light from the exterior to electrical impulses to the brain are the photoreceptors in the retina; there are two types: rods (they are responsible for our night vision and they only perceive black and white tones) and cones (they are responsible for our detailed vision and they perceive color);
  • optic nerve – this is the way the light travels from the retina to the visual cortex made up of millions of nerve fibers; once the impulses reach the brain, we can finally say that the process of vision is complete.

 

Because the eyes have so many components (and we haven’t even talked about them all!), there is also a multitude of conditions that can affect the sight and function of the eye. Besides astigmatism, some of the most common and known are:

  • cataract – it affects the lens which can become opaque causing blurred vision and a high sensitivity to light; usually, this condition is prevalent in older people and can be treated with replacement surgery; wearing protective sunglasses can act as a form of prevention for cataract;
  • hyperopia – it’s the inability to see clearly objects that are near;
  • myopia – by contrast, myopia is the inability to perceive objects that are at a distance clearly.

Astigmatism alongside hyperopia and myopia are also referred to as refractive errors because all these three conditions affect the way the light is refracted by the eye.

 

Astigmatism definition

Getting back to astigmatism, let’s try to understand what it is (astigmatism define), now that we have a general image of how the eyes work.

Astigmatism is an eye condition that is caused by the impossibility of light rays to focus correctly on the retina because of the curved shape of the cornea or the lens. If we speak in terms of sports, one common reference that might enlighten you is that in the case of astigmatism, the eye (astigmatism eye shape) is more like an American football ball, compared to the normal shape of the eye which is almost as round as a basketball.   

 

Astigmatism vision – astigmatism vs normal

Because of the irregular shape of the cornea or the lens, vision for people with astigmatism is especially blurry. This is because the curvature of the cornea creates two different focal points in which the light rays will focus in two locations in the retina.

 

Types of astigmatism

There are a few types of astigmatism that can be classified either considering the anatomical cause of this condition or by the location of the focal points.

According to the first classification, there are two types of astigmatism – corneal astigmatism and lenticular astigmatism. You’ve guessed it by now – corneal astigmatism is caused by shape irregularities of the cornea and lenticular astigmatism is caused by shape irregularities of the lens.

The second classification states that there are five types of astigmatism due to the fact that there are two focal points, instead of one (which is the case of a normal eye). These types are:

  • simple myopic astigmatism – the two focal points that the light rays reach are one just before the retina and one exactly on the retina;
  • simple hyperopic astigmatism – one focal point on the retina and one behind it;
  • compound myopic astigmatism – both focal points are before the retina, but in different places;
  • compound hyperopic astigmatism – both focal points behind the retina, but in different places;
  • mixed astigmatism – one focal point before the retina and one behind it.

 

Astigmatism symptoms

The most common symptoms of astigmatism are blurred or fuzzy vision, independent of the distance of the objects, eyestrain, headaches, squinting, impaired night vision. However, these symptoms vary among people with astigmatism, some of which don’t experience any of the symptoms. If you check some of the boxes or all of them, it might be time for an eye consultation.  

 

Astigmatism causes

While there isn’t a definite cause for astigmatism (at least it’s not discovered yet), genetics seems to play an important role. In the case of most people with astigmatism, the eye condition is congenital, meaning that they are born with it. However, astigmatism can also develop further down the line and can be a consequence of an injury of the eye or a complication after eye surgery. Very rarely, astigmatism can develop because of a rare eye condition known as keratoconus which causes the cornea to get thinner and thinner and to change its shape. Contrary to popular belief, you can’t develop astigmatism if you spend too much time in front of a blue-screen or reading in poor light.

 

Astigmatism risk factors

Since it’s usually present from birth, astigmatism is prevalent in kids and adults, but some other characteristics act as risk factors as well: having a parent or family member with astigmatism or keratoconus, excessive farsightedness or nearsightedness or history of eye surgeries.

 

Astigmatism in children 

As we’ve stated before, astigmatism can be present from birth. However, kids may not realize they have any issue with their vision enough to verbalize it, but astigmatism can put a strain on their vision process. This is why specialists recommend eye exams for kids at 6 months old, and at the age of 3 and 5 or 6. 

 

Astigmatism one eye?

Typically, astigmatism is a bilateral condition affecting both eyes. In some cases, though, only one of the two eyes can develop astigmatism, but this is usually due to a physical injury of the eye. However, even if the astigmatism is bilateral, the severity of the condition is usually different from one eye to the other.

Astigmatism versus lazy eye?

Is astigmatism the same thing as lazy eye? The short answer is no, but these two conditions are somewhat connected. Lazy eye, also known as amblyopia, is an eye condition in which one eye has weaker vision than the other. An imbalance in astigmatism – different levels of astigmatism between the eyes – can lead to amblyopia. If this astigmatism is present from childhood when the brain is in full developmental process, what usually happens is that the brain will set a preference for the eye that provides better stimuli, neglecting the other and causing a somewhat permanent imbalance between the two eyes.

 

Astigmatism and other eye conditions

It’s very common for astigmatism to co-occur with other eye conditions, usually other refractive errors. Most often, astigmatism is prevalent alongside myopia (nearsightedness) and hyperopia (farsightedness). Even though these optical conditions can be present together, it’s important to understand the differences between them.

Astigmatism vs myopia. Myopia, also known as nearsightedness or short-sightedness, is an eye condition that makes it difficult to see in the distance. What happens is that the eye elongates, causing light rays to focus before the retina. As a consequence, any object situated at a distance is perceived as blurry or fuzzy. Even though blurred vision is the main symptom of astigmatism as well, the main difference between astigmatism and myopia is that myopia means blurred vision at a long distance and astigmatism means blurred vision at any distance. Another difference concerns what causes these eye conditions: astigmatism is caused by the irregular shaping and curvature of the cornea or lens, while myopia is caused by the elongation of the eye. As a result, in astigmatism light focuses on two focal points on the retina, while in myopia light rays focus in front of the retina.

Astigmatism vs hyperopia. Hyperopia, also known as farsightedness, is a refractive error and eye condition that makes it difficult to see objects that are near. The cause of this condition is that the eyeball becomes shorter and so the light focuses behind the retina – basically, this condition is the exact opposite of myopia, where the eyeball is elongated and the light focuses in front of the retina. Just as we’ve stated in the case of myopia, astigmatism and hyperopia are different because in astigmatism all objects at any distance become blurry, while in the case of hyperopia only objects that are near are hard to perceive.

As we’ve mentioned before, some people can have astigmatism as well as myopia (astigmatism with nearsightedness; astigmatism with myopia) or hyperopia (astigmatism with farsightedness), but it’s essential to know the differences between these refractive errors and to diagnose them correctly in order to properly address them.

 

Stigmatism vs astigmatism

If you’re wondering what’s stigmatism and what’s the difference between stigmatism and astigmatism, look no further. Stigmatism is a term used mostly in geometric optics that refers to the characteristic of an optical system (much like the cornea or lens of the eyes) to focus light rays into a single focal point. One could say that stigmatism is what’s referred to as the “normal” way light should focus in the eye for a normal vision, which is why in optometry and ophthalmology this term it’s not really used. Astigmatism, on the other hand, refers to the presence of two focal points in which the light rays will focus on the retina, causing the blurry vision.

 

Astigmatism diagnosis

Astigmatism diagnosis

Which doctor should you visit for a diagnosis?

Astigmatism can be diagnosed after a thorough eye examination performed either by an ophthalmologist or an optometrist. Right now you’re probably wondering what’s the difference between the two so let’s briefly review what each profession is all about.

What is an optometrist? An optometrist is an eye care professional that can perform eye exams and vision tests, they can detect eye irregularities and abnormalities, diagnosing eye conditions and they can prescribe corrective lenses and medications for different eye conditions. In simpler words, an optometrist can provide primary vision care, but it’s not a medical doctor.

What is an ophthalmologist? In contrast with an optometrist, an ophthalmologist is a medical doctor specialized in primary vision care and the eyes. Another difference between the two professions lies in the level of training required for the two as well as in what they can diagnose and treat. An ophthalmologist can perform eye surgery, treat all eye conditions and they can prescribe corrective lenses and eyeglasses as well as medication.

Now that you know the difference between these two eye care professionals, it should be easier for you to decide which one you want to go to for a consultation. However, keep in mind that in case of astigmatism, either of the two are more than qualified to help with a diagnosis.

But how exactly is astigmatism diagnosed? The comprehensive eye examination performed for a diagnosis involves a series of activities and tests that we will discuss next.

 

Astigmatism tests

The very first astigmatism test performed by the medical professional will be a visual acuity test. After this, a keratometer and a phoropter will be used for a final diagnosis. Even though these sound like serious tests and instruments, you are not to worry since every one of these tests are painless and non-invasive.

Visual acuity test. This test means that you will have to read letters from an eye chart, from a certain distance, determining your vision’s clarity. Visual acuity is described as a fraction between the distance from the object and the distance your eyes need to be at in order for that object to be seen clearly. As a reference, 20/20 is the normal distance for visual acuity.

Keratometer. Keratometers are instruments used to measure the curvature and diameter of the cornea, providing information about the volume of the eyeball. This instrument is particularly important in prescribing the best contact lenses for your eyes because it provides the exact curvature level of a certain area of the cornea. This is achieved by measuring the reflection of a circle of light on the cornea.

Topographer. Topography or corneal mapping is quite similar a concept with keratometry, but it’s a fairly modern test and instrument that can provide 3D images of the cornea’s curvature and shape.

Phoropter. This is an instrument used by the medical professionals to place different lenses in front of your eyes in order to measure how they focus the light rays. To measure exactly how the light focuses and what’s they eye focusing power, the doctor uses a retinoscop or an automatic instrument.

After performing all needed tests, an ophthalmologist or an optometrist can finally diagnose astigmatism and move on to discuss treatment plans.

 

Astigmatism severity scale

Before we discuss about treatment options, let’s first see how astigmatism can vary from one person to another or even from one eye to the other. Just like any other refractive error, astigmatism is measured in diopters. A perfectly normal eye, without astigmatism, has 0 diopters. If someone has between 0.5 and 0.75 diopters, they may not need intervention since it’s quite a low degree of severity. However, starting from 1.5 diopters of astigmatism, glasses, contact lenses or even eye surgery may be recommended since the discomfort increases. On a prescription for contact lenses or glasses there are a few indicators used for describing your refractive error. The “spherical” boxes refer to myopia and hyperopia, while the “cylinder” boxes refer to astigmatism. A classification of astigmatism by the degrees of diopters is:

  • less than 1 diopter – mild astigmatism;
  • between 1 and 2 diopters – moderate astigmatism;
  • between 2 and 3 diopters – severe astigmatism;
  • more than 3 diopters – extreme astigmatism.

 

Astigmatism treatment options

Astigmatism treatment options

Can astigmatism be corrected and if so, how astigmatism is corrected?

There are three main ways you can ameliorate the symptoms of astigmatism and even correct it – glasses, contact lenses or eye surgery. All these depend on the severity of your astigmatism and its symptoms and, of course, on the degree in which your astigmatism is taking a toll on your quality of life.

Glasses. Eyeglasses are the primary treatment option chosen by people with astigmatism (astigmatism glasses). The lenses are cylindrical and are designed to compensate for the refractive error of astigmatism. However, if you have mild astigmatism, glasses may not even be needed, but if your astigmatism is accompanied by myopia or hyperopia for example, glasses can be a good option for you.

Contact lenses. Contact lenses are preferred by some because they can provide a larger vision filed and a clearer vision (astigmatism contacts; astigmatism lenses). There are a few types of contact lenses, not all of them being very efficient in the case of astigmatism (the standard lenses which are softer being one of them). The best contact lenses for astigmatism are corrective lenses which can be toric lenses (a type of soft lenses that is better for astigmatism) or gas-permeable lenses (a type of rigid lenses). Toric lenses can be worn during the day, deviating the light rays in the right directions. Gas-permeable lenses are rigid and don’t change their shape which makes them difficult to wear for long periods of time. This is why they are usually worn at night, during your sleep, time in which they correct the shape of the cornea (but only with a short-lasting effect, usually long enough to last until the next night).

Surgery. Astigmatism surgery is a type of refractive surgery that uses laser to change the shape of the cornea. The most common ones are LASIK surgery (astigmatism LASIK) and PRK. LASIK surgery acts to remove tissue from the inner cornea, while PRK also removes tissue from the superficial layer of the cornea.

 

Can astigmatism go away? On its own, no. To also answer the question of whether there is an astigmatism cure, unfortunately, the answer is also no. Being a refractive error caused by the change of shape and curvature of the cornea, astigmatism is quite irreversible. However, with the treatment options we have outlined before, the symptoms of astigmatism can be managed.

Do astigmatism get worse? The short answer is yes. Just like any other refractive error or eye conditions, if you don’t act and treat astigmatism, the changes in shape and curvature of the cornea or lens can progress and not in a good direction.

Is astigmatism bad? Except for the vision problems it causes, if it’s diagnosed and treated, astigmatism is not bad. However, in time, one of the complications that can arise from an untreated astigmatism can be lazy eye or amblyopia which we addressed before.

 

Astigmatism red dot

As you’ve probably guessed by now, astigmatism is an eye condition that can impair vision in case of training and shooting at an aim because virtually any type of target, including a dot, is perceived as blurry or fuzzy by someone with this refractive error. 

Astigmatism at night

Astigmatism can affect your vision at night (astigmatism night) since the contrast between different sources of light and the darkness makes for the blurry vision to be more pronounced. This happens because the pupil dilates which means that more light enters the eye which in turn causes more fuzziness. This also means that astigmatism can impact driving at night (astigmatism driving at night). If you start experiencing any sort of trouble with your vision, especially while driving, make sure to get an eye exam as soon as possible since it can be an indication of an underlying eye condition.

 

Conclusion

Astigmatism is an eye condition that turns any object at any distance into a blurry and fuzzy image. There are several ways to treat and manage the symptoms of astigmatism so don’t hesitate to contact a specialist that can diagnose and propose a treatment plan designed for your needs.

Articles

Other Articles