2023-11-10
． Text/Jia-Jun Xie
． Executive Editor/Li-Ling Gao
． Source/Health Editorial Department
Eyes are the windows to the soul. Many people undergo myopia surgery to get rid of the inconvenience of wearing glasses. However, before the advent of laser surgery, “RK myopia correction surgery” was mainly used 20 or 30 years ago.
Scarring on the cornea after cutting with a diamond knife can affect vision, causing significant changes in morning, midday and evening vision.
Myopia is caused by an excessive curvature of the cornea, according to Chi-Chin Sun, an attending physician at the Department of Ophthalmology at Keelung Chang Gung Memorial Hospital. This results in the image forming in front of the retina instead of on it. During the early years of RK myopic surgery, a diamond knife was used to make radial cuts on the cornea. The number of cuts increased with the degree of myopia, ranging from 4, 8, to 16. This procedure flattened the cornea, allowing the image to fall on the retina and restoring vision.
Yin-Shan Chen, director of the Department of Ophthalmology at Hsinchu Hospital of China Medical University, explains that during the procedure, doctors made vertical cuts in the cornea at 3 o’clock, 9 o’clock, 6 o’clock, and 12 o’clock. The scar will be thickest at the center where the cuts converge, obstructing the middle of the pupil. This can affect the line of sight and result in post-operative vision loss, blurred vision, and other issues.
Chi-Chin Sun stated that the deep incision of the cornea with a diamond knife makes the cornea fragile and unstable. To correct astigmatism, some patients are also given limbal incisions in addition to radial incisions, further destabilizing the cornea. Changes in intraocular pressure throughout the day can cause alterations in vision, resulting in alternating myopia or hyperopia. The patient’s vision is mostly impaired at night, which can make driving or performing tasks difficult.
Yih-Shiou Huang, director of the Department of Ophthalmology at the Linkou Chang Gung Memorial Hospital and Chang Gung Artificial Electronic Eye Center, explained that the cornea incision using the diamond knife is a manual operation that cannot make precise vision corrections. In the long run, the cornea becomes thin, leading to corneal degeneration and irregular astigmatism. Additionally, it is prone to cracking upon impact.
What’s even more problematic, as all three ophthalmologists mentioned, is that as patients get older and begin to develop cataracts, not only does the risk of corneal rupture increase during cataract surgery, but the cornea is unstable and the power calculation needs to be more precise. If the patient wishes to have a multifocal intraocular lens fitted, the image quality is likely to be poorer, making the cataract surgery much more difficult.
Corneal damage is irreversible. Laser myopia surgery solves the problems of scarring and corneal instability.
“The damage caused by RK myopic surgery is irreversible.” Although the fragile and unstable cornea cannot be reversed, Chi-Chin Sun pointed out that if there are scars or deposits in the center of the cornea that cause blurred vision, you can consider removing them directly with surgical curettage or laser. Combined with anti-scar drugs, good results can be achieved. On the other hand, corneal transplants may not be able to cover the whole area, and instability caused by limbal incisions may not be improved.
Chi-Chin Sun said that the damage caused by RK myopic surgery usually occurs slowly over the years. In fact, in recent years, we have seen many patients with related problems. They often have presbyopia and cataracts at the same time and cannot see clearly at a distance or close up. He reminded that if you had this operation in its early years, if your vision changes a lot during the day, sometimes it is normal, sometimes it is unclear, especially if your night vision is particularly poor, it is advisable to see a doctor as soon as possible.
As for current laser myopic surgery, Yih-Shiou Huang said that the laser cuts the cornea in a circular manner and then pulls out a corneal flap to change the curvature and thickness of the cornea to achieve the effect of correcting myopia. It does not leave any scars or scabs, and the thickness of the cornea changes evenly, so more thickness is retained and the cornea is relatively stable.
Can’t I use eye drops that contain ammonia? Eye drops containing steroids and preservatives should be used with caution
According to media reports, Li Jing had been taking various ammonia-containing eye drops for years, and the ammonia accumulated in the center of the cornea, leading to corneal fogging and irreversible serious consequences. Yin-Shan Chen, Chi-Chin Sun and Yih-Shiou Huang all said that they had never heard of anyone using eye drops containing ammonia. Yin-Shan Chen speculated that it might be sulfonamide eye drops. In ophthalmology, this is an “MSG drug” that is clinically prescribed to patients for “peace of mind.” This drug is not effective, but it does no harm and should have nothing to do with the loss of vision.
Yih-Shiou Huang reminded us that steroid eye drops are more important to watch out for. When the eyes are injured or inflamed, or after surgery, steroid eye drops can be used. They can reduce inflammation, swelling and clarity of the cornea or conjunctiva, and the effect is immediate and significant. However, if you do not follow your doctor’s advice and use them for a long time, they can cause an increase in intraocular pressure, which can lead to side effects such as glaucoma and cataracts.
In addition, many eye drops or artificial tears may contain preservatives. If they are not used excessively over a long period of time, they are generally harmless. However, they can be toxic to the cells in your eyes, causing the blood vessels in your eyes to dilate and your eyes to become red. If you use eye drops for a long time or frequently, it is recommended that you use preservative-free artificial tears or solutions.
