|Year : 1983 | Volume
| Issue : 6 | Page : 759-767
Surgical treatment of myopia.... with special references to posterior scleral support operation and radial keratotomy
Director Institute of Clinical Ophthalmology, 1-100 Umeda, Kiryu, Gunma, Japan
Director Institute of Clinical Ophthalmology, 1-100 Umeda, Kiryu, Gunma
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Momose A. Surgical treatment of myopia.... with special references to posterior scleral support operation and radial keratotomy. Indian J Ophthalmol 1983;31:759-67
The idea to correct refractive errors surgically is not new. According to Duke-Elder's "System of Ophthalmology", it goes back to 18th century. Since early 18th century, the extraction of the lens fromhigh myopic eyes has been tried, and finally, such a technique was standardized by Fukala and is known as Fukala's operation.
Reduction of refractive power in high myoipia by shortening of the glove, i.e. sclerectomy, started in early 20th century and this technique has been applied to high myopic eyes either with or without the retinal detachment.
Prophylactic surgery for high myopia was first suggested by Shevelev in 1930 with surgical support to the posterior pole of the eyeball, and since the, various surgeons have reported several techniques for this surgery.
Kerato-refractive surgery was first started by Sato in Japan in 1930s. Sato's technique fell in abeyance in Japan after 1960 due to advent of contct lenses and also development of corneal decompansation after the surgery. However, this technique which today is called "Radial Keratotomy" was rediscovered and modified by Fyodorov in 1970s. Since then, this surgery is being performed widely both in the Soviet Union and the United States of America.
For kerato-refractive surgery, there are several other techniques. Namely Wedge Resection for high astigmatism, Corneal Stromectomy, Keratomileusis, Hypermetropic Keratomileusis, Keratophakia, Epikeratophakia, Thermokeratoplasty etc.
In 1950s, implantation of concave anterior chamber lens in myopic eyes was tried, however, the result was not satisfactory.
These refractive surgeries have been highlighted in up-to-date ophthalmic surgery.
Out of the various techniques of surgical treatment of myopia, Ihave performed posterior scleral support operation and radial keratotomy.
Posterior Scleral Support Operation
As everyone knows, the pathological change of high myopia is characterized by the enlargement of the posterior pole of the eyeball, which is followed by macular hemorrhage and degeneration. In most cases of high myopia, the macula is involved after 40 to 50 years of age and the vision gradually deteriorates until the eye becomes almost blind.
The posterior scleral support operation aims to cover the thinned posterior pole of high myopic eyes with a supporting material to withstand the intra-ocular pressure, and thereby prevent further increase of the posterior staphyloma of the globe. There are several names assigned to this type of surgery [Table - 1] ). However, some of them do not suit well the purpose of this surgery and some are difficult to pronounce. I proposed to this surgery "Posterior Scleral Support Opoeration" in 1976. This name not only aptly describes the aim of this surgery but is also easy to pronounce.
Surgical techniques and supporting materials: There are three basic techniques of this surgery, namely X-shaped, Y-shaped and single strip support [Figure - 1]. I first tried Yshaped support in 50 eyes. However, if the two arms of the Y-shaped supporting material are pulled forcebly to the medial side, the optic nerve is pressed and the optic nerve atrophy may set in.
In X-shaped support, if two arms of the supporting material are pulled forcebly to the medial side, they may press the optic nerve, and if any one arm is pulled, the crossing of the Xshaped material decenters from the posterior pole.
In single strip support, the supporting material covers the posterior pole vertically between the optic nerve and the insertion of the inferior oblique muscle, and the optic nerve is not pressed. My present technique is the single strip support with Lyodura which is a modiiication over the technique of Snyder and Thompson in 1972, and Thompson in 1978 where a cadaver's sclera was used.
The best supporting material is the fascia lata of the same patient. However, the high part must be incised to obtain it. The second best material is Lyodura which is a lyophilized human dura from West Germany. It was originally developed to cover any defect of dura mater during neurosurgery. Lyodura has been sterlized by gamma ray and is free from antigenic, pyrogenic and non-collagenic substnces. Lyodura is biologically compatible with the eyeball and has a sufficient tensile strength. It may cause a slight but not severe inflammatory reaction after implantation. Lyodura is now also being used in plastic surgery of the lid and the in retinal detachment surgery.
Besides the fascia lata and Lyodura, an animal tendon and cadaver's sclera have been used. However, nobody recommends the use of artificial materials such as nylon or silicone. because it is expected that the implanted material gets organized and firmely covers the posterior pole. I do not use materials which are likely to be rejected, such as cadaver's sclera or an animal's tendon.
There are two schools of thought on the indication of this surgery. One favors application of this surgery to progressive myopia in children to arrest its progression. Others feel this surgery should he indicated for high myopia in adults which have macular changes. My own opinion is that it would not be too late to apply this surgery after first Fuch's spot appeared.
Surgical technique of the single strip support: The conjunctiva and Tenon's capsule are incised about 6 mm from the limbus around 270 degrees from the lateral side. The lateral, superior and inferior recti muscles are separated from the eyeball by a stravismus hook. Then, the strabismus hook is introduced behind the posterior pole and the connecting tissue is separated. The inferior oblique muscle is separated and pulled up by the strabismus hook.
A strip of Lvodura vrhich is 5 to 6 mm wide and 100 mm long, is passed under the lateral rectus and inferior oblique, then it is passed under the superior and inferior recti. The smooth surface without a trace of mcningeal vessels of the Lvodura is made to lace the sclera. It is most important to pass the Lvodura under all the fibers of the inferior oblique muscle, otherwise it will not pass over the posterior pole between the inferior oblique insertion and the optic nerve. It is also important to remember that the inferior oblique has a broad insertion under the lateral rectus.
The Lyodura is pushed down deeply towards the posterior pole, the eyeball is slightly rotated to the lateral side and both ends of the Lyodura are once crossed over the medial rectus muscle and tightened up. With this manipulation, the Lyodura comes in position covering the posterior pole vertically. Excess of the Lyodura is excised and both ends are sutured to the sclera on the medial side of the superior and inferior recti muscles. It is necessary to suture the Lyodura to cover the eyeball firmly, but not tightly. The conjunctiva and Tenon's capsule are closed together.
Three weeks after the posterior scleral support operation, lens extraction using cryo or aspiration-irrigation device is performed in most cases where myopia is over - 16 diopters or cataract is present. In some other cases where myopia is under - 13 diopters and cataract is not present, either a contact lens is prescribed or myopia case, both lens extraction and radial keratotomy were combined.
The extraction of the lens or the radial keratotomy makes the spectable correction of residual refractive error very easy. Usually after but possibly before the lens extraction, the entire fundus is examined, and if there is any lesion which may lead to the retinal detachment, it is coagulated by laser.
| Observations|| |
240 cases of the posterior sceral support opoeration by the single strip support technique have been performed since 1978. It is interesting to know that in 116 out of the 240 eyes where there was nocataract before the lens extraction, the mean full corrected vision improved from 0.35 before the posterior scleral support operation to 0.67 two months after the lens extraction. This improvement is probably a result of enlargement of the retinal image after the lens extraction and relaxation of the macula along with improvement of the circulation at the posterior pole. The average refractive power reduced from - 17.6 diopters to + 1.7 diopters.
In the rest of the cases where cataractous lens was extracted or radial keratotomy was combined, improvement of vision and reduction of myopia were also achieved.
The incidence of complications was low and optic nerve atrophy after the surgery did not appear in any case.
In early 1930s, T. Sato of Juntendo University of Japan made a historic observation, that after the rupture of the apex of keratroconus, the cornea flattend considerably and vision thereby improved. Hence in 1939, he devised a technique of incisions of the Descemet's membrane for keratoconus. And until early 1950s, he gradually modified this technique and created a technique of posterior or anteroposterior incisions of the cornea for myopia. He concluded that posterior incisions are more effective than anterior incisions. Probably, it was easier for him to cut the cornea from the posterior side, observing the tip of the knife just under the corneal surface making a sufficient depth of incisions in the cornea. Sato was a fine surgeon, but he was handicapped by not haveing an operation microscopeand not have a knowledge on the role of the corneal endothelium to maintain the transparency of the cornea. As mentioned before, his surgery was abandoned in Japan because of the advent of contact lenses and the sudden demise of Sato in 1960. Some 20 years after Sato's surgery, many cases developed bulluous keratopathy. In recent survey by Juntendo University, Sato operated on 681 eyes and 60 eyes returned to Juntendo University for Bullous keratopathy. S. N. Fyodorov of Moscow observed a case of corneal injury by a broken spectacle glass in 1972. The case was a 16 year-old boy and his eye was hit while wearing glasses by his friend. Broken glasses caused multiple incisions on his cornea, however, after the cornea healed, his myopia was also cured. Fyodorov started to modify Sato's technique of radial keratotomy.
Many people discussed the similarily of the present technique of radial keratotomy to Sato's technique and gave warning of a repeat of past failure, but there are some important fundamental differences between the past technique and the present technique which requires the safety of the procedure. The present technique was introduced into the United States of America by Reo Bores in 1978 and is not being widely performed in both countries.
Principal of radial keratotomy:
The present technique is to cut 85 to 90% of the central corneal thickness or 83% of the paracentral . corneal thickness only from the corneal surface under the microscopic control. Usually, 8 or 16 incisions are performed leaving 3.0 to 5.00 mm of the optical center zone intact. This procedure makes the cornea in the periphery and mid-periphery steeper by the intra-ocular pressure and consequently makes the cornea in the center flatter. The effect of this procedure is almost predictable and it can be controlled by changing the size of the optical centre zone, number of incisions and depth at the corneal periphery. This technique is indicated mostly for low and moderate myopia to restore a good distant vision without glasses. However, this technique can be applied for high myopia or only the worse eye of mypic anisometropia to reduce the power and make wearing glasses easy.
[Table - 2][Table - 3] are formulas to predict the effect of the surgery and to determine the size of the optical center zone of the cornea by Fyodorov. These formulas are very much complicated.
[Table - 4] is-ma simplified table by Schachar to predict the effect. After radial keratotomy was introduced into the United States of America, some changes in the technique have been made. The differences between the Russian technique and the American technique are : in the Russian technique, usually 16 incisions are made from the periphery to the centre using a rasor brade, and in the American technique, usually 8 incisions are made from the center to the peripherty by a diamond knife. The effect of 8 incisions is 85% of 16 incisions, and if the effect is not sufficient, another 8 incisions are added some time after the first incisions in the USA. However, 8 incisions have also been done in Fyodorov's institute recently and some American surgeons are being using the Russian technique.
As mentioned before, this surgery is indicated moistly to low and moderate myopia to restore a good distant vision in both the Soviet Union and the United States of America. However, the biggest complication of this surgery is over or under correction. For Japanese, Chinese and Korean people who have to read very small and complicated is injected retrobulbarly and a slight proptosis is made. Mannitol, Diamox and massage are not given.
A razor brade is adjusted so that it protrudes from the tip of micrometer knife an amount equal to 85 to 90% of the central corneal thickness. The optical center zone is marked with an optical center marker and the incision lines are marked with a corneal marker of 8 or 16 in cisions. The incisions are carried out from slightly incide of the limbus to the edge of the optical center zone along with the mark of incision lines. Usually, the incisions are made first from 12 o'clock to the center, then from 6 o'clock, 9 o'clock, 3 o'clock and four oblique lines in turn. The depth of incisions is examined by a depth gauge. At last, 10mg of Gentamycin is injected under the conjunctiva.
Chinese characters, over correction causes reading difficulty. Japaneses people even for a + 0.5 diopter hyperopia, often need glasses during school age and after 35 years of age. Hence my cases are all high myopia or the worse eye of myopic anisometropia and I indicate this surgery to reduce the refrctive power and to enable the patients to wear glasses confortably. Of course, Indian characters are not so small, this surgery can be performed in low and moderate myopoia in India, if the patient does not want to wear glasses or contact lenses.
For this surgery, some special instruments to perform precise incisions are necessary. They are Optical or Ultrasound Pachometer, Micrometer Knife, Caliper Block, Optical Center Marker, 8 and 16 cuts Corneal Marker and Depth Gauge.
My technique is a mixture of the Russian and the American technique. The size of optical centre sone is decided by Schachar's table. The pupil is constricted with pilocarpine. After akinesia and surface anesthesia, the surgery is started by having the patient fixate on the coaxial light source of the operation microscope and the site of reflex of the light of the operation microscope on the cornea, i.e., the optical centre of the cornea, is marked with a bent injection needle. The retrobulbar anaesthesia is then injected. If the intra-ocular pressure becomes low, precise incisions are difficult. Therefore, a large amount of weak anaesthetic, such as 7 to 8 cc of 1 % Xylocaine.
If the correction of the corneal astigmatism is necessary, several types of incisions to increase the effect along the steeper meridian are applied [Figure - 2].
| Observations|| |
30 days were operated until October 1982. These eyes were contact lens failed high myopia or contact lens failed worse eyes of anisometropia.
Pre-operative refractions of these eyes were from - 6 diopters to - 16 diopters and the average was - 11 diopters. The optical center zone was 3.0 mm in 28 eyes, 3.2 mm in one eye and 3.5 mm in one eye. Incisions for astigmatism correction were combined in two eyes. 8 incisions were done at the first sitting in all eyes and 8 more incisions were added in four eyes after three weeks.
The effect was maixmum on the following day of the surgery which gradually reduced and stabilized in three months. All cases became able to tolerate glasses. The reduction of myopia was from 5 to 7 diopters. The endothelial cell density reduced from pre-operative 3,551/mm 2sub to 3,314/mm2 at three months postoperatively. This amount of cell loss will never induce the bullous keratopathy in the future.
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[Figure - 1], [Figure - 2], [Figure - 3]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]