Radial keratotomy
Encyclopedia
Radial keratotomy is a refractive surgical procedure
to correct myopia
.
who removed glass from the eye of one of his patients who had been in an accident. A boy, who wore eyeglasses, fell off his bicycle and his glasses shattered on impact, with glass particles lodging in his eyes. A procedure was performed consisting of making numerous radial incisions which extended from the pupil
to the periphery of the cornea
in a pattern like the spokes of a wheel. After the glass was removed (by this method) and the cornea healed, he found that the patient's eyesight had improved significantly.
calibrated diamond
knife. It has been found that incisions that penetrate only the superficial corneal stroma are less effective than those reaching deep into the cornea, and consequently incisions are made quite deep. One study cites incisions made to a depth equivalent to the thinnest of four corneal-thickness measurements made near the centre of the cornea. Other sources cite surgeries leaving 20 to 50 micrometres of corneal tissue unincised (roughly equivalent to 90% of corneal depth based on thickness norms).
Accurate keratotomy is still popular to correct astigmatism
. It is also done with a diamond knife but in these cases, cuts are made circumferentially, parallel to the edge of the cornea.
The healing corneal wounds consist of newly abutting corneal stroma as well as fibroblastic cells and irregular fibrous tissue. Closer to the wound surface lies the epithelial plug, a bed of the cells that form the normal corneal epithelium, which have fallen into the wound. Often this plug is three to four times as deep as the normal corneal epithelium layer. As the cells migrate from the depth of the plug up to the surface, some die before reaching the surface, forming breaches in the otherwise healthy epithelial layer. This consequently leaves the cornea more susceptible to infection. This risk is estimated to be between 0.25% and 0.7% Healing of the RK incisions is very slow and unpredictable, often incomplete even years after surgery. Similarly, infection of these chronic wounds can also occur years after surgery, with 53% of ocular infections being 'late' in onset. The pathogen most commonly involved in such infections is the highly virulent bacterium Pseudomonas aeruginosa
.
to dilate, maximizing the amount of scattered light that enters the eye. In cases where large epithelial plugs lead to such aggravating symptoms, patients may seek further surgical treatment to alleviate the symptoms.
Increasing altitude can cause partial blindness in radial keratotomy patients, as discovered by mountaineer Beck Weathers
(who had had the surgery) during the 1996 Mount Everest
disaster
.
The incisions of RK are used to relax the steep central cornea in patients with myopia.
Popularized by Dr. Svyatoslav Fyodorov of Russia, the original technique of incisions from periphery to center was called the Russian technique (Gulani AC, Fyodorov S: Future Directions in Vision course, June 1997) while the later advances of performing controlled incision from center to periphery was called the American Technique (Gulani AC, Neumann AC: Refractive Surgery Course, Feb 1996).
Radial keratotomy enjoyed popularity during the 1980s and was one of the most studied refractive surgical procedures. Its 10 year data was published as the PERK (Prospective Evaluation of Radial Keratotomy) study, which proved the onset of progressive hyperopia often found a decade after the original surgery is due to continued flattening of the central cornea.
A conceptually opposite technique of using hexagonal incisions in the periphery of the cornea is known has Hexagonal Keratotomy or HK (described by Dr. Antonio Mendez of Mexicali, Mexico), which was used to correct low degrees of Hyperopia. The idea of HK was to make six peripheral incisions to form a hexagon around the central cornea to steepen the hyperopic flat cornea and thereby focus the rays of light onto the retina. These incisions could further be of two types: connecting and non-connecting (Gulani AC: 10 Refractive Procedures for Hyperopia. ISOPT 2001).
Patients with Radial Keratotomy (RK) may present with a variety of incisions. They can have 4,8,16 or 32 incision surgeries and also all kinds of patterns and linearity based on their refractive errors, surgeon's style or training when it was initially done. Many of these patients have had additional incisional surgeries like Astigmatic Keratotomy or AK where incisions are placed at the steepest points of the cornea in patients with astigmatism
to relax and transform the cornea to a more spherical shape. Some patients have had a combination of intraocular surgeries such as Pseudophakia or Phakic implants along with their keratotomies and many of them also underwent purse-string suture to control the over-correction (Dr. Green’s Lasso suture).
Technological challenges of how to calculate the IOL power post RK surgery for an associated cataract
as well as the aberrations induced along with stability questions exist.
The presenting visual complaints are outlined in a new classification system below wherein the patient could be presenting with hyperopia as stated by the PERK study and that too at an age of Presbyopia (both require Plus lenses to correct them and therefore are a compounded problem) or with associated age-related deterioration from cataracts. Due to the instability of the cornea along with age-related pathologies, many physicians find it difficult to address these patients' visual acuity satisfactorily. In these situations, the factors to be considered include:
Primary Visual factors:
Secondary (Associated) Visual Factors:
sets in. Some also develop cataracts. Their vision can still be restored with epilasik, PRK, LASIK
or phakic lens extraction, or cataract surgery. The corneal curvature has to re measured and modified by history, central keratometry or contact lens method.
Refractive surgery
Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea or cataract surgery. The most common methods today use excimer lasers to...
to correct myopia
Myopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
.
Discovery
The procedure was discovered by Svyatoslav FyodorovSvyatoslav Fyodorov
Svyatoslav Nikolayevich Fyodorov was a Russian ophthalmologist, eye microsurgeon, professor, full member of the Russian Academy of Sciences and Russian Academy of Medical Sciences and politician...
who removed glass from the eye of one of his patients who had been in an accident. A boy, who wore eyeglasses, fell off his bicycle and his glasses shattered on impact, with glass particles lodging in his eyes. A procedure was performed consisting of making numerous radial incisions which extended from the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
to the periphery of the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
in a pattern like the spokes of a wheel. After the glass was removed (by this method) and the cornea healed, he found that the patient's eyesight had improved significantly.
Procedure detail
In radial keratotomy (RK), incisions are made with a precisionAccuracy and precision
In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...
calibrated diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
knife. It has been found that incisions that penetrate only the superficial corneal stroma are less effective than those reaching deep into the cornea, and consequently incisions are made quite deep. One study cites incisions made to a depth equivalent to the thinnest of four corneal-thickness measurements made near the centre of the cornea. Other sources cite surgeries leaving 20 to 50 micrometres of corneal tissue unincised (roughly equivalent to 90% of corneal depth based on thickness norms).
Accurate keratotomy is still popular to correct astigmatism
Astigmatism (eye)
Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea or lens. There are two types of astigmatism: regular and...
. It is also done with a diamond knife but in these cases, cuts are made circumferentially, parallel to the edge of the cornea.
Postsurgical healing
Pseudomonas aeruginosa
Pseudomonas aeruginosa is a common bacterium that can cause disease in animals, including humans. It is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in hypoxic atmospheres, and has, thus, colonized many...
.
Side effects
Large epithelial plugs may cause more scattering of light, leading to symptoms of flare and 'starbursts'. This can happen especially in situations like night driving, where the stark glare of car headlights abounds. These dark conditions cause the pupilPupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
to dilate, maximizing the amount of scattered light that enters the eye. In cases where large epithelial plugs lead to such aggravating symptoms, patients may seek further surgical treatment to alleviate the symptoms.
Increasing altitude can cause partial blindness in radial keratotomy patients, as discovered by mountaineer Beck Weathers
Beck Weathers
Seaborn Beck Weathers is an American pathologist from Texas. He is best known for his role in the 1996 Everest disaster that has been the subject of many books and films, most notably Into Thin Air and Everest.-Everest:...
(who had had the surgery) during the 1996 Mount Everest
Mount Everest
Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...
disaster
1996 Everest Disaster
The 1996 Mount Everest disaster refers to the events of 10-11 May 1996, when eight people died on Mount Everest during summit attempts. In the entire season, fifteen people died trying to reach the summit, making it the deadliest single year in Mount Everest's history...
.
The incisions of RK are used to relax the steep central cornea in patients with myopia.
Popularized by Dr. Svyatoslav Fyodorov of Russia, the original technique of incisions from periphery to center was called the Russian technique (Gulani AC, Fyodorov S: Future Directions in Vision course, June 1997) while the later advances of performing controlled incision from center to periphery was called the American Technique (Gulani AC, Neumann AC: Refractive Surgery Course, Feb 1996).
Radial keratotomy enjoyed popularity during the 1980s and was one of the most studied refractive surgical procedures. Its 10 year data was published as the PERK (Prospective Evaluation of Radial Keratotomy) study, which proved the onset of progressive hyperopia often found a decade after the original surgery is due to continued flattening of the central cornea.
A conceptually opposite technique of using hexagonal incisions in the periphery of the cornea is known has Hexagonal Keratotomy or HK (described by Dr. Antonio Mendez of Mexicali, Mexico), which was used to correct low degrees of Hyperopia. The idea of HK was to make six peripheral incisions to form a hexagon around the central cornea to steepen the hyperopic flat cornea and thereby focus the rays of light onto the retina. These incisions could further be of two types: connecting and non-connecting (Gulani AC: 10 Refractive Procedures for Hyperopia. ISOPT 2001).
Patients with Radial Keratotomy (RK) may present with a variety of incisions. They can have 4,8,16 or 32 incision surgeries and also all kinds of patterns and linearity based on their refractive errors, surgeon's style or training when it was initially done. Many of these patients have had additional incisional surgeries like Astigmatic Keratotomy or AK where incisions are placed at the steepest points of the cornea in patients with astigmatism
Astigmatism
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances...
to relax and transform the cornea to a more spherical shape. Some patients have had a combination of intraocular surgeries such as Pseudophakia or Phakic implants along with their keratotomies and many of them also underwent purse-string suture to control the over-correction (Dr. Green’s Lasso suture).
Technological challenges of how to calculate the IOL power post RK surgery for an associated cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
as well as the aberrations induced along with stability questions exist.
The presenting visual complaints are outlined in a new classification system below wherein the patient could be presenting with hyperopia as stated by the PERK study and that too at an age of Presbyopia (both require Plus lenses to correct them and therefore are a compounded problem) or with associated age-related deterioration from cataracts. Due to the instability of the cornea along with age-related pathologies, many physicians find it difficult to address these patients' visual acuity satisfactorily. In these situations, the factors to be considered include:
Primary Visual factors:
- Quantitative:
- Decreased visual acuity (Myopia, Hyperopia, Astigmatism)
- Qualitative:
- Irregular astigmatism
- Small Optic Zone
- Incisions
Secondary (Associated) Visual Factors:
- Presbyopia
- Cataracts
- Corneal Scars
- Corneal Instability (thin / ectasia / trampoline effect)
Visual rehabilitation after RK
As shown by the PERK study, patients who underwent radial keratotomy continue to drift toward hyperopia (far sightedness). Many of these patients have reached the age when presbyopiaPresbyopia
Presbyopia is a condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the...
sets in. Some also develop cataracts. Their vision can still be restored with epilasik, PRK, LASIK
LASIK
LASIK or Lasik , commonly referred to simply as laser eye surgery, is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism...
or phakic lens extraction, or cataract surgery. The corneal curvature has to re measured and modified by history, central keratometry or contact lens method.