PKR to the hyperopia after radiaire keratotomii
PKR to correct hyperopia after radial keratotomy
Keratotomii radaire (KR) is a technique that allowed to correct nearsightedness by conducting deep corneal incisions, arranged in a star (where the term "radiaire"); and intended to provoke a central flattening of the cornea. This technique was the first operation of refractive surgery offered routinely to short-sighted patients, the late 1980s and early 1990s. The KR has been abandoned in the mid-1990s for the benefit of the excimer laser surgery (procedures to Refractive aiming - PKR then LASIK), much more accurate, and which, unlike that of the radial keratotomy, is stable in time.
The incisions of radial keratotomy are willing to 'Star', and their (even) number usually varies between 4 and 16 (2 to 8 pairs of incisions). The number of incisions is proportional to the degree of preoperative myopia.
The radial keratotomy exposes to a late complication called 'hypermetropique shift', which is characterized by the gradual emergence and the accentuation of a farsightedness. This hypermetropisation seems to be linked to excessive corneal flattening, which is manifested also by daily fluctuations of vision. PKR (surface excimer laser) is an effective technique to correct hyperopia induced by the radial keratotomy.
Radiaire keratotomii: principles and historical
The idea to make incisions in the corneal tissue to change the curvature is old: it's the Norwegian Shiotz, which was the first ophthalmologist to describe the use of an incision of the cornea to correct theastigmatism (1).
Some years later, Lans published the first experimental work on the effects of the corneal not puncture incisions in rabbits. These results allowed the founding principles of the corneal incisionnelles techniques (2)
-radiaires cuts cause a peripheral camber and a central flattening of the cornea.
-transversal incisions cause a loosening of the Meridian on which they focus.
-more incisions are deep, and the effect is more marked.
If the radial keratotomy technique was popularized by Russian Fyodorov, attributed to the Japanese doctor Sato the paternity of the technique of radial keratotomy. It was observed that the realization of spontaneous posterior tear of the Descemet membrane (part of the cornea) caused a secondary flattening in patients with Keratoconus. He designed a special knife intended to be introduced into the anterior Chamber of the eye and make incisions in the deep surface of the cornea to correct nearsightedness. Many patients were operated in Japan in the early 1950s, and the first results were published in 1953 (3).
At the time, it was unclear the role of corneal endothelium (located on the deep surface of the cornea). Unlike the eye of rabbit, the endothelium of the human eye does not recur. The relaxing corneal incisions made at the back of the cornea, causing damage to the endothelium of irreversibly, were originally from the onset of swelling of the cornea: it is estimated that more than 70% of patients with Sato technique have developed some severe swelling of the cornea. It should be noted that Sato is recommended to achieve 40 incisions to the posterior side, and 40 to the front of the cornea.
During a visit to the Japan, the surgeon Russian ophthalmologist Fyodorov met Akiyama, a student of Sato, who had taught him the technique of his master. Back in the USSR, he used it to try to correct the myopia of some of his patients, but was disappointed by the initial results that he obtained with the technique of Sato. The prior art of radial keratotomy was also taken up by his colleague Yenaliev, who obtained more encouraging results thanks to a technique made more reproducible by control of the depth of the radiaires incisions. This led Fyodorov to back this technique at the end of the 1970s for the correction of myopia: the results published by Fyodorov in 1982 (4) were very encouraging... but never matched later.
The American Bill realized the first radial keratotomy in the USA in 1978. At that time, the recommended number of incisions was 16: this number was lowered gradually, because studies showed that 4 incisions were sufficient to correct low myopia to medium (5). The sense of achievement of the incisions (centripetal: leaf towards the Center, or centrifugal from the Center to the blade) was also the issue of a fight between Refractive Surgeons debate. It was important to not continue the incisions too far to the Center under penalty to increase the risk of halos and duplication of the vision. Instrumentation also progress with the development of knives made in diamond blade; However, to create incisions, Fyodorov had used out of fragments of razor blade, that he was simply staring at on a "door blade!
In 1981, a study called PERK (Prospective Evaluation of Radial Keratotomy) was launched to study the results of a standardized procedure prospectively with the realization of 8 incisions on an optical area of 3 or 4 mm according to the initial refraction.
In total, the PERK study allowed to enlist 793 eyes of 435 patients with myopia was between 2 and 8.75 D. A year after the surgery, 60% of the eyes were to +/-1 D of the emmetropia, 30% were under corrected, and 10% were corrected more of a diopter. Five years after the intervention, the percentage of eyes with a farsightedness was 17 percent; This trend to the hypermetropisation was confirmed to the visit of 10 years (6), as 43% followed eyes had then developed a 'hypermetropique shift' more than one diopter. The risk of hypermetropique shift was higher among the patients who had a myopia more important, for which the Central optical zone (free from traces of incision) was narrower.
radial keratotomy technique is based on a central flattening of 'indirect' origin, linked to relaxation by the peripheral cornea strips section.
To fix strong corneal astigmatismes, achieving incisions transervsales ("Transverse cuts" or "T-cuts") were sometimes carried out, share and more arched Meridian, and perpendicular to the path of the radiaires incisions.
At the end of the 1990s, the introduction of the refractive surgery by excimer laser offered to refractive surgeons incomparably greater precision for corneal refractive surgery than that which could be obtained with techniques incisionnelles, not only in terms of local action (the precision of laser ablation is of the order of a micron), but also on a conceptual level. Indeed, rather than inducing a central flattening in an indirect way, through peripheral incisions, it became possible to sculpt a corneal 'ideal' according to a mathematical model profile accurate and less empirical. Despite the cost represented by the acquisition of an excimer laser, the radial keratotomy was quickly abandoned in favor of the PKR.
The hypermetropique shift is by far the most worrisome side effect observed after radial keratotomy. It is sometimes concomitant with the existence of refractive fluctuations, which cause a change of vision between sunrise and sunset. In some patients, the secondary hypermetropisation seems to continue over the years, and sometimes results in having to prescribe fixes in scope of the order of 3 or 4 diopters, often associated in our experience to a noncompliant astigmatism (said astigmatism ' inverse'). This refractive drift is even more annoying that it occurs in patients operated in the 80s and 90s, when they had 30 years on average. Today, these patients have all reached or passed the age of presbyopia, and rely for reading glasses, or a correction, in addition to their correction by far.
However, the realization of a technique of laser surface can be offered to most of the patients operated of radial keratotomy victims of a secondary hyperopia. She gives encouraging results, allowing patients to strongly reduce their dependence on corrective lenses. A detailed preoperative assessment is necessary to validate this type of information. It includes the realization of a topography of the cornea.
Corneal topography after radial keratotomy
Corneal topography is a systematic review to evaluate the result of a process of radial keratotomy.
Topographic examination reveals characteristic aspects, with the most spectacular can be the change of the posterior corneal topography. Indeed, the radial keratotomy is the only technique that causes a marked change after cornea geometry, since the entire corneal wall suffers the biomechanical effect of cuts... In laser surgery, corneal profile changes are restricted to the front of the cornea.
There is thus a parallelism between the anterior and posterior elevation maps, where you will find a profile aspherical oblate marked (appearance in "roundel", the center of the cornea being colored in cool colors because located under the sphere of reference). The computation of the factor of asphericity (Q) provides a positive value, and the spherical aberration induced is positive type.
Since the KR involves no removal of corneal tissue, the Central thickness and distribution of the peripheral corneal thickness is unchanged. Its discreet and irregular incisions corollary is some topographic irregularity, which generates a high rate of high degree of original corneal aberrations.
The PKR to correct hyperopia post-radial keratotomy
Surface laser excimer (PKR) techniques are to issue a correction based on the sculpture of the corneal stromal surface excimer laser. Myopia, astigmatism and farsightedness are accessible to this type of correction. Even if LASIK is the technique of choice to correct farsightedness, the realization of a LASIK is not desirable after KR, as geometry of the cornea is quite changed, and that the risk of reopening of the corneal incisions of keratotomii leading to a break-up of the flap exist. The presence of epithelium within the stromal incisions also facing complications specific to the level of the interface (the interface from the incisions epithelial invasion).
The PKR does not expose these complications because it doesn't involve creation of an interface. It is intended to increase the Central curvature of the cornea, to increase the optical power (vergence), whose failure explains hyperopia (see the) profile of ablation for the correction of hyperopia).
The technique after KR is of achievement similar to that performed on non operated corneas. It is to remove the epithelium of the cornea on an area whose diameter is between 8 and 9 mm, and then deliver the laser correction; before asking a lens bandage for a few days.
The laser is intended to recambrer the central cornea: it is issued on the stroma désépithélialisé (putting naked layer of Bowman) averaged periphery.
If the PKR is usually done on a bilateral basis in routine, it is sometimes interesting to perform the procedure in a sequential manner (ex: one month apart) in farsighted patients, but having been made of radial keratotomy in the past. Indeed, the technique results are less predictable than for Virgin corneas of any surgery. The results obtained on the first eye surgery can be used to "refine" the correction of the second eye.
In my experience, and that of many Refractive Surgeons (7,8), the correction of hyperopia post KR is an effective technique, because it allows to reduce systematically the dependence on glasses for farsighted patients after radial keratotomy, and become presbyopic at midlife. In certain indications, the use of a personalized treatment (guided by the Wavefront or corneal topography) seems interesting to increase the regularity of corneal profile. Freinateurs healing agents (Mitomycin C) are often used to limit the risk of regression of the treatment by excessive scarring.
Certainly, its accuracy is less than on corneas without surgical history, and the intensity of the phenomena of remodeling post-operative impose to aim a light sur-correction, to anticipate the regression of the induced effect. You have to be patient: stabilization of the result is between 3 and 6 months after the completion of the PKR.
No severe complications were observed in the course of a PKR to the hyperopia post-KR, outside a regression partial of the effect printed by laser, sometimes accompanied by a pronounced scar reaction (haze). This reaction is about the periphery of the optical zone, and doesn't have a significant Visual impact.
So the refractive benefit of the PKR after radial keratotomy is variable, but relatively constant. The multifocalite induced by hypermetropique profile (coupled with that which is usually induced by the incisions of radial keratotomy) allows the patient to reduce significantly its dependency to prescription glasses. The Asphericity oblate marked reduction reduces the rate of positive spherical aberration and allows an improvement in the quality of vision.
Here is the map topo-aberrometrique of a cornea performed before PKR to the hyperopia post radial keratotomy:
A surface photoablation (PKR) was issued to correct hyperopia by aiming a slight over-correction to allow the eye to see up close without correction (myopisation). Six months after the intervention, the uncorrected Visual acuity is by far 5/10 and 10/10 close without glasses.
The presence of a high rate of corneal irregularities is a potential indication for the issuance of a custom photoablation. In the following example, the patient, 51 years old and operated from radial keratotomy in the 1990s, complained for a decade of 'triple vision' of the left eye, which is also farsighted. The triple (triplopie) vision in one eye is a symptom whose causes are generally similar to those of the double vision (diplopia) eye.
In this example, the triple vision is explained by the irregularity of the cornea, and the presence of a rate high a high degree optical aberration called trefoil. Reviewing aberrometrique allows to quantify these anomalies and the simulation of the retinal image of a light spot (PSF) actually reveals a division into three lobes.
In this situation, the simple correction of hyperopia from + 2.50 D would allow the patient to win uncorrected Visual acuity, but would not necessarily solve the triple perception of bright lights. The remediation strategy must move towards a (custom) personalized correction guided by corneal topography. Indeed, it is here the deformation of the cornea which is responsible for the symptoms.
In this mode of correction, a previous corneal topography is made (Topolyzer Vario) and transmitted by network excimer laser. The EX500 (Wavelight) excimer laser software interprets this topography, and sets a custom ablation profile taking into account the corneal topographic irregularities.
This profile presents here 3 peripheral main lobes, and virtually no photoablation at the centre (as for the correction of hyperopia). This type of ablation arch selectively the flat areas of the cornea, and regularize the corneal profile in addition to reducing the hyperopia.
Reviewing topo aberrometrique carried out a few months after the issuance of this custom photoablation allows you to see the correction of hyperopia and significant improvement of Visual quality. The patient reported the disappearance of the triplopie; uncorrected Visual acuity by far is equal to 10/10. There is also a significant improvement in Visual acuity closely (Parinaud 4 without correction, against Parinaud 16 without correction before the procedure).
In conclusion, hyperopia after radial keratotomy is not a fatality. Laser correction results are very encouraging and allow many patients to find a better quality of vision and reduce their dependence on glasses for distance and near vision.
(1) Schiotz HA. Ein Fall von hochgradigern Hornhautastigmatismus nach Starextraction. Besserung auf operational Wege Arch Augenheilk, 1885; 15: 178-181
(2) Lans LJ. Completed investigations uber project von astigmatism durch nicht-perforiende corneawunden. Graedes Arch invest, 1898; 45: 117-152
(3) Sato T. Akiyama K, Shibata H. A new surgical approach to myopia. Am J invest, 1953; 36: 823-829
(4) SN, Agranovski A.A. Fyodorov. Long term results of anterior radial keratotomy. Ocular Therapy Surg 1982; 1: 217-223
(5) Salz JJ, Villaseñor R, Elander RA et al. oven-incision radial keratotomy for low to moderate myopia. Ophthalmology 1986; 93:727 - 738
(6) GO Waring, III, Lynn MU, McDonnell PJ, and the PERK study group. Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery. Arch invest, 1994; 112:1298 - 1308
(7) Anbar R, Malta JB, JB Barbosa, Leoratti MC, Beer S, Campos M. also keratectomy with mitomycin-C for consecutive hyperopia after radial keratotomy. Cornea. 2009; 28 (4): 371-4
(8) Ghanem RC, Ghanem VC, Ghanem EA, Kara-José N. Corneal wavefront-guided also with mitomycin-C keratectomy for hyperopia after radial keratotomy: two-year follow up. J Cataract Refract Surg. 2012; 38 (4): 595-606.