The Science Of Health: Welcome back to “The Science Of Health“, ABP Live’s weekly health column. Last week, we discussed what egg freezing is, how human oocytes are retrieved, and the benefits of egg freezing are. This week, we discuss why LASIK is performed, how the eye surgery technique works, and why it is not always successful.
LASIK, which stands for laser-assisted in situ keratomileusis, is a refractive surgical procedure which uses a laser to treat and correct vision problems caused by refractive errors, and is intended to reduce a person’s dependency on glasses or contact lenses.
Why LASIK is performed
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As the full form of LASIK suggests, this special technique of eye surgery is performed using lasers. The fact that it is an “in situ” technique means that the surgery is performed in the original place, where the refractive errors are located. Keratomileusis is derived from two Greek words, and means “corneal reshaping”. This is performed to correct the refractive power of the eye and improve vision by reshaping the cornea in the original place using an excimer laser, a type of high pressure, pulsed gas laser that produces intense ultraviolet light with high efficiency and high peak power at several useful wavelengths.
The cornea is the transparent part of the eye that covers the iris and pupil, and focuses light into the eye, enabling a person to see things.
An excimer laser is a special type of cutting laser that helps precisely change the shape of the dome-shaped clear tissue at the front of the eye, or the cornea, to improve vision.
The cornea of a person with normal vision refracts light precisely and focuses it towards the retina at the back of the eye, while in people with near-sightedness (myopia), far-sightedness (hyperopia), or astigmatism, an imperfection in the curvature of the eye’s cornea or the lens that results in blurred vision in all directions, the cornea does not refract the light properly.
Blurry vision is also known as refractive error, and is caused as a result of a mismatch between the curvature of the cornea, and the length of the eye.
Since the light is not refracted precisely, it is not focused accurately on the retina, resulting in blurred vision. Therefore, glasses and contact lenses and LASIK surgery allow the light to be bent properly, and reach the retina, so that a person can see things clearly.
How LASIK works
While glasses and contact lenses are temporary solutions to vision problems, LASIK is a permanent solution because it surgically changes the shape of the cornea.
According to the US Food and Drug Administration (FDA), a mechanical microkeratome, which is a blade device, or a laser keratome, which is a laser device, is used to cut a flap in the cornea. A keratome is a surgical instrument used for making an incision in the cornea. After cutting a flap in the cornea with a keratome, a hinge is left at one end of the flap. This flap is folded back to reveal the stroma, which is the middle section of the cornea. A portion of the stroma is vapourised using pulses from a computer-controlled laser, and the flap is replaced.
ABP Live spoke to Dr Vipul Mandaviya, Cataract & LASIK Surgeon, Shivam Eye Hospital, Surat, and Dr Ajay Sharma, Chief Medical Director, EyeQ, a chain of eye centres in India, and asked them about the detailed scientific procedure of LASIK, and the cases in which LASIK fails.
Explaining why an excimer laser, which is an ultraviolet laser, is used to remove a thin layer of corneal tissue to reshape the cornea, Dr Mandaviya said this process helps achieve optimal refraction of light on to the retina, and makes the cornea become thinner. “This outpatient procedure typically takes around 10 to 15 minutes to perform on each eye.”
In order to numb the surface of the eye, local anaesthetic in the form of eye drops is administered.
“The surgery is conducted while the patient remains awake, and medication is used to induce relaxation. LASIK can be performed on one or both eyes during a single session,” Dr Mandaviya explained.
The thin flap on the cornea is created either using a microkeratome, or a femtosecond laser, Dr Sharma said. According to the American Academy of Ophthalmology, a femtosecond laser is an infrared laser with a wavelength of 1053 nanometres, and works by providing photoionisation of the cornea.
“The surgeon carefully lifts this flap to access the underlying corneal tissue. Using an excimer laser, a small amount of tissue is precisely removed to reshape the cornea and correct the vision problem. The corneal flap is then gently repositioned, requiring no stitches. As the cornea heals, improved vision results from the corrected shape, allowing light to focus correctly on the retina,” Dr Sharma explained.
Therefore, Dr Mandaviya said, the flap is created in the corneal tissue so that the surgeon can lift it and allow the excimer laser to reshape the underlying cornea. He explained that the flap remains attached to the cornea through a hinge to prevent complete separation. Earlier, microkeratome, a specialised automated knife, was used to create the flap, but now, a femtosecond laser is used, because it is a safer approach.
“The amount of corneal tissue to be removed by the excimer laser is determined in advance by the surgeon, taking into account factors such as the patient’s glasses or contact lens prescription, results from a wavefront test that measures light travel within the eye, and the surface shape of the cornea. Upon completion of the reshaping process, the surgeon repositions and secures the corneal flap, eliminating the need for stitches. The cornea naturally holds the flap in place,” Dr Mandaviya said.
Who can undergo LASIK?
People who wish to undergo LASIK surgery must meet certain criteria, including being 18 years of age or older, having a refractive error which can be treated using LASIK, having an eye prescription which did not change much in the last year, and having thick and healthy corneas.
However, there are certain candidates who must not opt for LASIK. According to the American Academy of Ophthalmology, these people include those with an unstable refractive error, severe dry eye, corneal scars or tissues, advanced glaucoma (a group of eye conditions that damage the optic nerve), a history of having certain eye infections, extreme levels of myopia, hyperopia or astigmatism, thin corneas, keratoconus or cone-shaped cornea, a cataract affecting vision, and diabetes that is not controlled well, among other factors.
Pregnant or breastfeeding women must not undergo LASIK surgery because vision changes can happen during pregnancy. An ophthalmologist checks numerous factors before deciding whether a person is fit to undergo LASIK surgery. These factors include measurements of the cornea, pupil size and refractive error, the amount of tears the eyes make, and overall health of the eyes.
Explaining why LASIK surgery is not recommended for people with dry eyes or corneal disorders, Dr Mandaviya explained that the process of creating a thin flap in the cornea to reshape its curvature can disrupt the nerves responsible for tear production and distribution, leading to a temporary or long-term increase in dry eye symptoms. “If a person already has pre-existing dry eye syndrome, LASIK can exacerbate the condition and make the symptoms worse.”
He said that certain corneal disorders, such as keratoconus, corneal dystrophy corneal scars and corneal infections can affect the structural integrity of the cornea, making it unsuitable for LASIK. Keratoconus is a condition characterised by a progressive thinning and bulging of the cornea, causing it to become cone-shaped. Corneal dystrophy refers to abnormal corneal tissue development.
“Since LASIK involves reshaping the cornea, any pre-existing irregularities or weakness in the cornea can lead to unpredictable results, compromised visual outcomes, or potential complications,” Dr Mandaviya said.
According to Dr Sharma, dry eye syndrome causes discomfort, irritation and blurry vision due to insufficient tear production or poor tear quality, and hence, the creation of a corneal flap and reshaping of the underlying tissue during LASIK can disrupt the stability of the tear film and worsen dryness symptoms.
He explained that people with corneal disorders like thin or irregular cones may not be suitable candidates for LASIK because these conditions can compromise the structural integrity and stability of the corneal flap, increase the risk of complications, and lead to suboptimal results.
Instances in which LASIK fails
While LASIK is a wonderful feat of medical technology, and restores corrected vision in a large number of people, it is not always successful. According to experts, the instances in which LASIK fails are the ones where people had unstable prescriptions, abnormal corneal maps, advanced glaucoma, severe dry eye, squint, significant eye muscle abnormalities, uncontrolled diabetes, autoimmune disorders, incorrect surgical technique, inadequate healing response, or complications post surgery.
Dr Mandaviya explained that LASIK is most effective when the eye prescription has remained stable for at least a year, and therefore, it is important to note that LASIK corrects the current eye prescription, because if the prescription is likely to change in the future, undergoing LASIK earlier may result in the need for an additional correction later. He said it is therefore recommended to wait until the prescription stabilises before considering the surgery.
Dr Mandaviya explained that abnormal corneal maps, which can be seen through corneal topography, allow for the identification of underlying corneal abnormalities such as keratoconus or suspected keratoconus, conditions which can progress or worsen after LASIK surgery. “If the topography reveals any abnormalities, it is advisable to decline the procedure.”
Since LASIK involves reshaping the cornea using a laser, which can cause a thinning of the cornea to some extent, the patient having thin corneas ahead of the surgery can result in complications if they undergo the process, Dr Mandaviya said.
He explained that patients with advanced glaucoma, who require multiple medications to control the condition, or have significant visual field defects, are usually not recommended to undergo LASIK because performing the surgery may interfere with glaucoma management and worsen their condition.
According to Dr Mandaviya, individuals with severe dry eye syndrome are generally advised not to undergo LASIK surgery unless their condition improves and there are no permanent underlying causes.
Certain individuals might be at risk of developing squint following the surgery. This susceptibility is determined through evaluation before the surgery. In such cases, people are advised to delay LASIK surgery, Dr Mandaviya said.
People who suffer from uncontrolled diabetes or autoimmune disorders are usually recommended to avoid LASIK surgery because proper healing can be impeded following the procedure, and the risk of corneal complications and infections may increase.
Dr Sharma said it is important to determine the suitability of LASIK for an individual, based on their individual circumstances, and hence, patients who intend to opt for the procedure must consult with a trained eye care professional. “Eye care professionals possess the expertise to evaluate a patient’s eye condition comprehensively, and provide personalised advice regarding the appropriateness of LASIK.”
He concluded that by seeking professional guidance, individuals can make informed decisions about their vision correction options.
Other risk factors and complications for LASIK
According to the USFDA, risk factors for LASIK include use of certain medications such as corticosteroids like prednisone, having a history of conditions such as herpes infection, and inflammation inside the eye, a history of eye injury, or previous eye surgery.
The complications of LASIK include dry eyes, sensitivity to light, blurred vision, and visual symptoms such as glare, halos, starbursts and double vision. While these symptoms are usually mild, they can become severe and permanent, leading to loss of vision, interference with visual activities, and pain. There is also a possibility that a person’s vision is not fully corrected after LASIK, because of which they may require an additional surgery to get the desired outcome, according to the USFDA.
The vision correction may not be long-lasting, and could worsen over time. There may be a need for patients to continue wearing glasses even after LASIK surgery.
One of the drawbacks of LASIK is that it cannot reverse presbyopia, FDA Patient Safety Expert Anita Rayner was quoted as saying in a video by the USFDA.
Presbyopia is a refractive error of the eye which makes it difficult for middle-aged and older adults to see things up close because the lens stops focusing light correctly on the retina, according to the US National Institutes of Health (NIH).
Sometimes, the side effects of LASIK can be so severe, that people who never required glasses before surgery may have to wear glasses for reading.
Therefore, patients with vision problems who intend to undergo LASIK must carefully read everything about the surgical procedure, understand the risk factors, consult with a licensed eye care professional, and be sure of what they expect from the process.
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