What is Astigmatism?
Astigmatism is a common eye condition. It occurs when your eye doesn’t focus light evenly onto the retina, the light-sensitive tissue at the back of the eye. This could mean that light rays entering the eye aren’t able to converge or meet at one specific point and instead form lines.
Astigmatism can occur in different ways. It can be due to the shape of the cornea, the lens inside the eye, or could even relate to the retina. The condition can be classified as regular or irregular, with several subtypes including “with the rule”, “against the rule”, “oblique”, and “bi-oblique”.
Astigmatism can also be categorized into simple, compound, and mixed types. People with astigmatism often complain of eyestrain, discomfort, blurry vision, seeing objects stretched out, and problems with focusing. Some noticeable signs could include partially closed eyelids, a tilted head, an irregularly-shaped optic disc, and varied strength in different directions of vision. To diagnose this condition, doctors may carry out several tests such as retinoscopy, a slit lamp exam, keratometry, Schiempflug imaging, astigmatic fan, and the Jackson cross-cylinder evaluation.
Treatment options for astigmatism include eyeglasses, contact lenses, and certain surgical procedures, including laser vision correction, toric IOL implantation, and astigmatic relaxing incisions.
What Causes Astigmatism?
Astigmatism is a condition that affects the shape of the eye causing vision problems. It has various types:
1. Corneal Astigmatism: This is the most common type and occurs due to an abnormal curve of the cornea, the clear front surface of your eye.
2. Lenticular Astigmatism: This isn’t due to the cornea but rather the lens of the eye becoming abnormally curved, tilted or displaced. Different areas of the lens can also have varying refractive (light-bending) effects causing this type of astigmatism.
3. Retinal Astigmatism: This occurs when the ‘macula’, the part of the eye responsible for sharp, detailed vision, isn’t aligned correctly.
4. ‘With the Rule’ and ‘Against the Rule’ Astigmatism: These types occur when the two primary lines of sight (known as meridians) are at a right angle, but one is more curved than the other. In ‘With the Rule’ astigmatism, the vertical line is more curved, while in ‘Against the Rule’ astigmatism, the horizontal line is more curved.
5. Oblique Astigmatism: In this case, the two main lines of sight are right-angled to each other but aren’t perfectly horizontal or vertical.
6. Bioblique Astigmatism: Here, the main lines of sight aren’t at right angles to each other at all.
7. Simple Astigmatism: This occurs when light is focused in front or behind the retina on just one meridian.
8. Compound Astigmatism: This happens when light is focused in front or behind the retina on both meridians.
9. Mixed Astigmatism: It occurs when light is focused in front of the retina along one line of sight and behind the retina on the other.
There are numerous potential causes of astigmatism, ranging from genetic conditions like keratoconus to surgical procedures like LASIK or injuries to the eye. Conditions affecting the surface of the eye like ulcer or scars, wearing contact lenses, cataracts and some tumors can also cause astigmatism.
Risk Factors and Frequency for Astigmatism
Astigmatism is a condition that changes as people age. When children are between 0 and 4 years old, they usually have high level of astigmatism that results in a steep cornea. The astigmatism experienced at this age is commonly against the general trend or ‘against-the-rule’. As children grow older (between 4 and 18 years), their cornea becomes flatter, and the level of astigmatism decreases. What’s normal at this age is to experience a small amount of with-the-rule astigmatism. From 18 to 40 years, the cornea stays mostly stable with a slight amount of with-the-rule astigmatism. After 40 years, the cornea starts to become steep again and the astigmatism changes to against-the-rule.
The amount and type of astigmatism can also vary depending on your ethnic background. For example, Native Americans are more likely to experience with-the-rule astigmatism. Unfortunately, poor nutrition can also lead to less rigid corneas. Among Asian populations, there are higher rates of change in astigmatism due to the unique characteristics of their eyelids. There’s a reported incidence of astigmatism of 1.00D or more in 42% of school children.
Various studies have demonstrated the prevalence of astigmatism in different populations. For instance, research from Brazil showed a myopia prevalence of 2.7% in the population but a much higher incidence of astigmatism at 16%. Interestingly, they discovered a predominance of against-the-rule astigmatism. In another study focused on Bangladeshi children living in East London, there was a high incidence of with-the-rule astigmatism.
Signs and Symptoms of Astigmatism
Astigmatism is an eye condition where people experience symptoms such as headaches, eye pain, heaviness in the eyes, trouble focusing, temporary blurring, drowsiness, and sometimes nausea. They may also have blurry vision, decreased vision, and see elongation of objects depending on the severity of the astigmatism.
It’s not unusual for a person with astigmatism to hold objects close to their eyes when reading. It’s also important to note any history of eye trauma, surgery, or other conditions like keratoconus, pterygium, or limbal dermoid.
Healthcare providers will perform detailed examinations using a torch light or a slit lamp to check for other conditions that could be causing the astigmatism. They’ll look for things like eyelid issues, dry eyes, or a corneal scar.
The lens of the eye will be closely examined for any changes, dislocation, and traumatic cataracts. Doctors also check the optic disk and macula through a dilated fundoscopy to rule out any other factors.
The common symptoms of astigmatism include:
- Headaches
- Eye pain
- Heaviness in the eyes
- Difficulty focusing
- Transient blurring
- Drowsiness
- Nausea (occasionally)
- Blurred and diminished vision
- Elongation of objects
During a physical exam, doctors look for:
- Eyelid issues
- Dry eyes
- Corneal scar
- Changes or dislocation in the lens
A person’s medical history may reveal factors like:
- Previous eye trauma or surgery
- Keratoconus
- Pterygium
- Limbal dermoid
Testing for Astigmatism
Visual acuity, which is how well you can see, is usually checked using either a Snellen’s chart or an E-chart. Your eye doctor will document three types of visual acuity: uncorrected (how well you can see without glasses or contact lenses), best-corrected (how well you can see with glasses or contact lenses), and pinhole visual acuity.
Retinoscopy is another test your eye doctor may use. It helps them understand more about your astigmatism (if you have one), specifically its direction and magnitude. They can also neutralize your refractive correction and observe specific reflexes in your eyes like dull, absent, or scissor-like reflexes that could indicate diseases like keratoconus. Additionally, your eye doctor might notice different power on two different axes in your eyes during this procedure.
Keratometry and computerized topography are used to map your cornea, which is the clear front surface of your eye. These tests can show different curvatures on two different axes of your cornea.
Pachymetry is important to measure your cornea’s thickness. This information can help your eye doctor decide if you’re a good candidate for refractive surgery, such as LASIK.
Finally, astigmatic fan tests and Jackson cross-cylinder tests can help to confirm the axis and power of the cylinder in your eye, which is important when diagnosing astigmatism.
Treatment Options for Astigmatism
For regular astigmatism, we often recommend wearing spectacles with special lenses that help correct the problem. Another option is hard contact lenses that can correct up to 2-3 dioptre of astigmatism. For those with astigmatism higher than that, we might suggest toric contact lenses.
When it comes to treating astigmatism, the method depends a lot on its severity. For mild cases up to 0.5 D, we usually only correct it if it’s causing symptoms. It’s important to be accurate when determining the degree of astigmatism and prescribing the correct lenses.
For those with a higher degree of astigmatism, we aim to fully correct it to reduce any symptoms. This might involve adjusting the prescription gradually, as some patients may initially find full correction uncomfortable and need time to adjust. A series of regular check-ups is needed to make sure the correction is working effectively.
When prescribing new glasses or lenses, we may need to recheck the axis of astigmatism, taking into account the previous prescription. It’s crucial to allow the patient time to get used to the new correction and to reassure them that any initial discomfort will lessen over time.
Oblique, mixed, and high astigmatism are often better treated with contact lenses than glasses.
There are also surgical options to manage astigmatism. One option is toric IOL implantation, which can handle corneal astigmatism and cataractous changes concurrently.
Astigmatic Keratotomy (AK) is another surgical technique that involves making cuts in the cornea to help reshape it. This procedure can treat up to 4 to 6 D of astigmatism, though it also carries risks such as irregular astigmatism, micro-perforations, and the possibility of overcorrection.
Limbal Relaxing Incision (LRI) is a safer incision used to correct mild astigmatism. This technique causes less discomfort and glare than AK, and the incisions generally heal faster.
Laser treatment methods, such as Photoastigmatic Refractive Keratotomy or Astigmatic LASIK, are also effective at correcting astigmatism. However, patients must be aware that these procedures require marking the axis of astigmatism in a sitting position, as the position may change when lying down.
Patients who suffer from astigmatism post-keratoplasty, a type of cornea transplant, can benefit from several techniques. These include adjusting the sutures, making incisions to help relax the eye, or using LASIK procedures. Severe cases of astigmatism, exceeding 20 D, might necessitate repeating the keratoplasty procedure.
What else can Astigmatism be?
- Nearsightedness (myopia)
- Farsightedness (hypermetropia)
- Difficulty in reading or seeing at close range, common in older adults (presbyopia)
What to expect with Astigmatism
If astigmatism is treated promptly, the outlook is generally good since there are many ways to correct it. When left untreated, particularly in children, it could lead to a permanent decrease in sight quality and “lazy eye” or amblyopia.
Astigmatism may vary over time, necessitating changes in prescription glasses and contacts. Correcting the eye’s focus often reduces or removes astigmatism in most instances. However, people with a condition called keratoconus can experience vision loss due to severe astigmatism. Therefore, regular and timely check-ups are essential.
Possible Complications When Diagnosed with Astigmatism
People with eye problems may have different symptoms. Some common ones include:
- Poor or blurry vision
- Warped or distorted vision
- “Lazy eye”, also known as amblyopia
- Seeing multiple images, also known as polyopia
- Eye misalignment, also known as strabismus
- Infections caused by contact lenses, known as contact lens-induced infective keratitis
Recovery from Astigmatism
Patients who have surgery to correct their astigmatism usually need to use specific eye drops after the surgery. If they had Photorefractive Keratectomy (PRK), they would use a combination of antibiotic and steroid eye drops (0.5% moxifloxacin and 0.25% loteprednol) several times a day for two weeks. Along with these, eye lubricants like 0.5% Carboxymethylcellulose is also recommended for three months.
For those who undergo Laser-Assisted in Situ Keratomileusis (LASIK), the same combination of antibiotic and steroid eye drops is typically used four times weekly, with the usage of eye lubricants continuing for three months.
Administrating these eye drops after cataract surgery to manage astigmatism is the same as the recommended routine following regular cataract surgery.
In certain cases, patients might be given a different combination of steroid and antibiotic drops such as 0.5% gatifloxacin and 0.1% dexamethasone, which need to be administered in a decreasing frequency over a week. Next, they would take plain antibiotic eye drops such as 0.5% gatifloxacin or moxifloxacin four times a day for fifteen days. It’s important that patients understand the necessity of taking these medications as instructed and regularly checking in with their doctors.
Preventing Astigmatism
It’s important to explain to the patient that astigmatism is a type of eye condition that may need to be addressed quickly. Patients should be aware that to understand the cause of astigmatism, certain basic tests are necessary, and without timely treatment, it can lead to reduced vision and even lazy eye in children.
Another essential information for the patient is the importance of checking family members for astigmatism and a related condition known as keratoconus. The patient should also understand that in some situations, treating astigmatism may involve surgery, and there might still be some minor residual astigmatism in a few cases.
