Astigmatism is a common treatable condition in which your eye isn’t completely round. The cornea and the lens should be smooth and equally curved in all directions to converge light rays sharply onto the retina at the back of your eyes for a clear vision. However, if the lens or cornea is not evenly curved the light rays won't be refracted properly. This leads to blurring of vision.
When the shape of the cornea is distorted it leads to corneal astigmatism whereas distortion of the lens curve is known as lenticular astigmatism.
Risk factors of Astigmatism
Astigmatism may be present from birth or it can develop in adults following an eye injury, eye disease, or surgery. The risk of developing astigmatism is high if:- You have a positive family history of astigmatism or other eye conditions such as keratoconus, which is a degenerative disease of the cornea.
- You have extreme difficulty seeing near or far object (extreme myopia or extreme Hypermetropia)
- You have suffered an injury to your eye or have undergone a cataract surgery
Signs and Symptoms of Astigmatism
A patient with astigmatism presents with:- A blurred vision
- Headache
- Difficulty seeing at night
- Eye strain and squinting
- Difficulty seeing distant objects (Myopia) or near objects (Hypermetropia)
- Double vision
Diagnosis of Astigmatism
Your doctor will conduct one of the following methods to test your eye for astigmatism and assess its severity. During the diagnosis, the power of lenses to improve your vision will also be determined.- Visual acuity test: In this test, you will be required to read letters, numbers, or symbols present on a chart at a distance of 20 feet from you. The results of the test are given as fractions. Normal visual acuity is 20/20.
- Keratometry: In this test, the curvature of your cornea will be measured using an instrument called the keratometer. The measurements of the test help assessing the shape of the cornea and its ability to focus light. The measurement also helps to determine the correct size of the contact lens required.
- Refraction: In this test, an instrument called a phoropter is used where your doctor places a series of lenses in front of your eye and you will be asked to read the chart placed at a fixed distance. The results of the test help find a lens that appropriately corrects your vision. Your input is key in determining the vision requirements.
Using the results of these tests your doctor will be able to determine if you have astigmatism or not.
Management of Astigmatism
There are multiple methods of treatment for correcting astigmatism, which your doctor will recommend based on the severity of the disease to best meet your visual requirements.- Glasses: Your doctor may recommend you use eyeglasses having cylindrical lenses. Glasses are easier to wear and are non-invasive methods of counteracting astigmatism. Lenses present in the eye bend the incoming rays of light to your retina, giving you a more clear vision.
- Contact Lenses: Some patients benefit more from contact lenses than glasses for astigmatism. Contact lenses are directly worn in the eye and provide a wider range of vision in some patients. It is however very important to keep these lenses clean to maintain eye hygiene.
- Orthokeratology: In this method, irregular curvature of the cornea is corrected temporarily by using a rigid contact lens for a limited period. It is helpful in patients with moderate astigmatism to achieve temporary symptom relief. It does not however treat the condition and the original astigmatic vision is restored if the patients stop wearing these rigid lenses.
- Refractive eye surgery: Using LASIK eye surgery or a photorefractive keratectomy your doctor changes the shape of your cornea so it can correctly focus light. In LASIK surgery tissues are removed from the inner layer of your cornea whereas in PFK the tissues are removed from the superficial regions of the cornea as well. After refractive surgery, you will not require to wear spectacles or contact lenses. Though after some surgeries you may be required to wear contact lenses for few days, prolonged use is not required.
Recent Advances and Treatment Modalities Currently Undergoing Clinical Trials
- Wavefront Guided Scleral Lenses: Special contact lenses called the scleral lenses are useful in treating irregular astigmatism caused following a surgery or an eye trauma or disease. These conditions are not adequately mitigated using just glasses or disposable soft contact lenses. Scleral lenses help reduce symptoms in such cases and improve vision. In most patients, however, though the symptoms are considerably reduced still some aberrations remain in vision which impairs their quality of life. A clinical trial is currently underway to assess the efficacy of customized waveform guided scleral lenses over traditional scleral lenses in treating aberrations of vision and improving quality of life. These customized lenses are made according to specific measurements of the eye of the patient using wavefront aberrometer measurements.
- Anesthetic Impregnated Bandage Soft Contact Lens: Photorefractive keratectomy is the preferred method of refractive surgery in cases with high refractive error, thin cornea, and astigmatism. However, it is associated with considerable pain and downtime compared to a LASIK surgery. A clinical trial is currently being done to assess the efficacy of proparacaine ( an anesthetic) impregnated bandage contact lenses in reducing pain associated with Photorefractive keratectomy. It is currently in Phase 4 of its clinical trial.
- Visian Toric ICL: Visian toric ICL is an FDA approved implantable lens designed to correct astigmatism associated with myopia. A clinical trial to assess the long term application of toric implantable contact lenses in correcting myopic astigmatism is being carried out.
- Vision-R800 Phoropter: A phoropter is a device used to test your eyesight. It helps detect the severity of the refractive error and is useful in prescribing glasses or contact lenses to correct it. A randomized clinical trial is currently underway assessing the efficacy of Vision – R800 phoropter in detecting refractive errors and prescribing corrective lenses for correcting those disorders. These devices are thought to measure the refractive errors more precisely and are associated with more patient and practitioner comfort. Precise detection of refractive errors helps in the effective correction of astigmatism.
References:
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Scott A Read , Stephen J Vincent, Michael J Collins. The visual and functional impacts of astigmatism and its clinical management. Ophthalmic Physiol Opt. 2014 May;34(3):267-94. doi: 10.1111/opo.12128. (https://pubmed.ncbi.nlm.nih.gov/24635572/)