Answer:
Myopia occurs when the eye's lens focuses images in front of the retina, blurring distant objects. This is often due to an elongated eyeball or the eye's refractive power being too strong for its length. Astigmatism is a condition where the eye's curvature isn't uniform, causing light to refract unevenly and resulting in distorted or blurred vision at all distances. This is usually caused by an irregularly shaped cornea, sometimes by an abnormal lens. Both conditions often stem from a combination of genetics and environmental factors such as prolonged close-up work, limited exposure to outdoor light, or excessive use of electronic devices.
People with these refractive errors typically wear glasses or contact lenses to improve vision. However, these can be inconvenient and affect appearance. Laser refractive surgeries like LASIK, Femto-LASIK, and SMILE can correct both myopia and astigmatism by reshaping the cornea using laser technology based on a personalized corneal map.
Specifically, excimer or femtosecond lasers reshape the cornea along each refractive axis, creating a more regular shape and allowing light to focus accurately on the retina. Regular astigmatism, where the principal meridians of the eye are perpendicular, can be effectively corrected with cylindrical lenses or laser surgery. When programmed precisely, the laser can reshape the cornea along these axes, focusing light directly onto the retina. Most patients achieve maximum unaided vision after surgery.
However, the effectiveness is limited in cases of irregular astigmatism due to corneal scarring, eye injuries, or suspected keratoconus. Keratoconus is a condition where the cornea thins and bulges outward, distorting vision and increasing light sensitivity. Laser refractive surgery can worsen corneal distortion in such cases and is generally contraindicated to avoid serious post-operative complications.
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A doctor performing refractive surgery. Illustrative photo: Tam Anh General Hospital |
The degree of astigmatism treatable with lasers is also limited, typically up to 4 or 5 diopters. For higher degrees, doctors may recommend toric implantable collamer lenses (ICL Toric) or artificial lens replacement, especially for those over 40 with cataracts.
Refractive surgery doesn't alter the eye's biological structure; it reshapes the cornea to adjust the light path, not addressing the underlying causes of congenital or structurally based astigmatism. Post-surgery vision can still change slightly over time, especially with eye strain or other medical conditions.
In your case, a comprehensive eye exam is necessary, including refraction measurements to determine the degree and stability of myopia and astigmatism. Corneal thickness, biomechanical strength, and corneal mapping are also crucial to detect any underlying abnormalities. The doctor will consider individual factors like age, occupation, specific visual needs, and post-operative care compliance to determine the most suitable procedure.
MSc. MD Tang Ngoc Anh
Deputy Head of Ophthalmology Department, High-Tech Eye Center
Tam Anh General Hospital, TP HCM
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