|
4 Diagnosis and Remedy
* Diagnosis
1 ) Ametropia Test
Visionary disorders (myopia, hyperopia, astigmatism) are called ametropias. The examination of the level of severity is called ametropia test. There are objective and subjective ametropia tests.
Objective ametropia tests can be classified into two types. One is the Auto refractor method that utilizes machine, and the other is skiascopy, in which the tester will shed light and test the patients vision by switching the level of lens, using a tool called skiascope.
Subjective ametropia test is a method that relies on testee's reaction. They are used to confirm the results from objective tests. Subjective tests include utilizing astigmatic dial, cross c's, red-green testing, blurry vision method(comparing the vision of two eyes using low level of correction lens). Among them, utilizing astigmatic dial and cross c's produce the most accurate results for discovering astigmatism.
2) Corneal topographic pattern test
The Corneal topographic pattern test refers to determining the height of the corneal by having the patients lie on their backs and display the results like topography maps. Contour maps differentiate the height of the region by displaying different colors, and so does corneal topographic pattern. The pattern is a type of corneal contour map, in which regions with high refraction rates are displayed in red colors, and regions with low refraction rates are displayed in blue. The test facilitates the understanding of corneal shape.The astigmatism level can be calculated through the pattern. The test also shows protruding regions that display typically high or low refraction rates, and displays astigmatic axis.* Remedy and Complications
1) Remedy
A Glasses
Wearing glasses is the most common remedy. As described above, it is rare a patient only has astigmatism alone. Therefore, he/she will be wearing glasses that correct myopia or hyperopia along with astigmatism. When astigmatism isn't very severe, patients often wear glasses that correct myopia or hyperopia.
Unlike myopia or hyperopia, astigmatism can cause some problems when the exact examines levels of lens is applied to the set of glasses. Especially for patients who used to wear glasses that did not correct astigmatism(or maybe did not wear glasses at all), wearing astigmatism glasses can cause distorted image perception and cause dizziness. The case applies for people with sudden increase in astigmatism level, patients who display two different astigmatism level in their eyes, and patients who have inclined axis.
Even if glasses clarifies vision, wearing them can be painful it they cause discomfort and dizziness. While young children adjust quickly to the initial stages of discomfort quickly, adults often have trouble getting used to the change and must look for alternatives.
The clarified vision is not the only objective. The glasses must also be comfortable and shouldn't cause dizziness. Therefore, rather than strictly following the results from refraction tests, one must find balance between improved vision and comfort of the user of the glasses.
B Contact Lenses
For people who have difficulty in wearing glasses(due to profession, or cares about appearances), or experience dizziness, contact lenses can be good alternatives. Contact lens option can be classified into soft contact lens and rigid-gas permeable contact Lenses(RPG Lenses).
Although small level of astigmatism won't make a difference, levels over 0.75~1.5 diopeter cannot be corrected effectively with soft contacts because ordinary soft contacts do not have astigmatism correction features. The alternative for this situation could be astigmatism-specific soft contacts that require time to adjust and astigmatic axis must be fit well. In order to correct astigmatism using soft contact lenses, the lenses must stay steady in a certain direction.
Therefore, including prisms on the surface or differentiating designs have been thought of the align the direction of the lenses, but the vision can still be unstable if the contacts rotate even just a little bit. For sever astigmatic vision with over 2.0~2.5 diopter level, it is very difficult to correct vision with astigmatism-specific soft contacts.
RPG lenses can correct severe astigmatism visions that soft contacts find difficult to relieve. The RPG lenses are the most common contacts for severe conditions. Although light level of astigmatism can be corrected using spherical contacts, most severe cases of astigmatism utilize non-spherical contact lenses.
Hard surfaces of RPG lenses allow the lenses to maintain its shape on the surface of the pupil. Therefore, even if the contacts rotate on the surface, it does not interfere with the correctional effect. Compared to astigmatism-specific soft contacts, RPG lenses provide much steadier vision for astigmatism patients.
However, RPG lens itself gives discomfort in the eye and requires people some time to adjust. Although the cases are rare, some patients with residual astigmatism display worse vision when they use RPG lens instead of soft contacts. Also, the location of the RPG lens on pupil's surface is greatly affected by the movement of the eyelid. Considering such downside, one must consult thoroughly with the doctor for prescription.
RPG contacts can partially correct irregular astigmatism that soft contacts and glasses cannot, and can alleviate severe astigmatism from conical cornea, too. However, for very severe conditions of conical cornea or high irregularity of corneal surface requires corneal transplants as the remedy.
C Refraction Correction Surgeries
Nowadays, great advances in Corrective surgeries such as LASIK or LASEC have been achieved, and such remedies can correct not only myopia or hyperopia but also accompanied astigmatism.
For severe myopia patients who are not eligible or LASIK or LASEC, artificial lens insertion could be an alternative, since the inserted lens also have astigmatism correction types and patients can choose the method that fits the condition of their eyes the most. For astigmatism lens utilized in insertions complications such as rotation of the lens within the eye have been reported.
D Surgical remedies
Other conducted remedies include Corneal Insections, Corneal Peritomy, Plastic Ring(Intacts, Keraring ) Insertions. Corneal Insections are used rarely nowadays due to its downside of weakening the strength of the pupil for exterior impact. Corneal Peritomy has its limits of astigmatism level that it can correct, and therefore is only utilized for auxiliary measure for other surgeries such as cataract surgeries. Plastic Ring Insertions have not been reported of long-term results and still have potential risks.
Recently, artificial crystalline lens that can reduce astigmatism levels during cataract surgeries have been developed, and widely become distributed. Testimonials up to present seem promising because the remedy has been reported to cause very little rotation of the lens within the eye. However, long-term outcomes have not been reported and the remedy has limits that it is hard to implement to patients without cataract symptoms.
2) Complications
Since astigmatism cannot technically be classified as a disease, there exist no specific complications. However, irregular astigmatism caused after surgery or due to infections cause distorted vision, and cannot be corrected with glasses, soft contacts, nor RPG lenses.
|
