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For the surgical correction of the keratoconus of type I, II (and III)
Introduction
Materials and methods
Surgical indications
Surgical approach
Results at 48 months of follow up
Discussion
Introduction
The Author presents herein the clinical results after the surgical treatment of the keratoconus with the "Asymmetric Radial Keratotomy" (referred to as A.R.K.), conceived by Prof. Massimo Lombardi and utilized and controlled in his Institute for the past nine years on an average selected group of type I-II-III.
The results are:
a) the stop of the keratoconus growth;
b) the stop of the progressive corneal thinning;
c) the correction of the spherical and cylindrical ametropia in the treatment of the keratoconus of type I, II and selected cases of type III.
The long term pathology appears to be completely stabilized (the first cases were treated with "symmetrical radial keratotomy" approximately nine years ago - 1986).
The purpose of this research is to emphasize the validity of A.R.K. in reference to type I, II and III (selected cases) keratoconus.
Materials and methods
A complete analysis precedes the examination which is divided into different phases according to the following parameters:
1) Pachymetry
2) Keratometry
3) Intraocular pressure
4) Corneal diameters
5) Ametropy (cycloplegic)
6) Endothelial microscopy with endothelial cell count and study of the cellular morphology
7) A-Scan biometry
8) Age
9) Sex
10) E.A.S. (Examination Anterior Segment) for shape section analysis, evaluation of the optical zone transparence and profile comparison (pre and post-operation).
11) Topographic Modelling System (T.M.S.).
In bilateral cases we usually operate on the eye in the best condition first, postponing for a couple of months the second eye in worse condition. In the meantime the second one undergoes a medical therapy based on vitamins A, E and c and drops of Physiomer (stabilized Isotonic saline and sterile Sea water).
Many variables have an effect on the final result such as the following:
1) Diameter of the optical zone
2) Number of incisions
3) Depth of incisions
4) Possible re-deepening
5) Size of the treated asymmetric corneal area (from 30° --> 180° --> 270°)
6) Quality of the blade (the best diamonds and the common RK markers are fine for the treatment)
7) The surgeon's ability to perf orm a regular and costant 80% incision depth.
8) Surgeon's experience in incisional surgery.
The purpose of Radial Keratotomy is to flatten the central part of the cornea with radial and symmetrical corneal incisions where the effect increases as they become longer and deeper. For A.R.K. surgery the length of the incisions is not so important and the result of the surgery is the flattening of the extroflected central and paracentral optical surface of the cornea.
Surgical indications
1) Keratoconus of type I;
2) Keratoconus of type II;
3) Keratoconus of type III (Selected cases).
A) Technical counter-indications
1) Patients with less than 300 microns pachymetry on the conus apex;
2) Patients with an ophthalmometry more than 60.
3) Central thick leucomas (E.A.S. section and retroillumination analysis) interfering with visual axis.
B) Clinical counter-indications
1) Relapsing corneal infections;
2) Relapsing mycotic infections;
3) Heavy dry eye syndrom;
4) Patients with psychological weaknesses, etc.
Surgical approach
The A.R.K. consists in performing micro-incisions always respecting the optical zone as widely as possible performed (from 4 to 5.5 millimeters). The incisions are in acentripetal manner. We must:
1) designate the optical zone;
2) delimitate the degrees (30° à 270°) of treatment following the T.M.S. map;
3) calculate the number and the depth of incisions on the basis of the pachymetry. Decisions regarding the surgical program change according to the different cases, while the surgeon's experience in the field of refractive surgery plays afundamental part.
While performing the incisions, according to our statistic, unwanted micro-perforations can rarely happen and they don't normally need any treatment (rare case of suturing with 10-11 0 nylon suture). These microperforations were accidental and due to the excessive irregularity of the the cornea's thickness, particularly in those cases where keratoconus was in amore advanced phase (III).
The microperforations had no statistically significant effect on the final result.
The normal rule is to incise no more than 80% of the thickness.
Results at 48 months of follow up
We can observe the values resulting from 48 eyes, all with at least 48 months of follow up.
We can evidence the reduction of both the spherical and the cylindrical ametropia by the clinical finding of 20/20 result of best uncorrected vision in a 20% of patients.
After 6 months, the ophthalmometry and the pachymetry were stable in the entire follow-up.
During the post-operational period, the patients may have had some troubles such as photophobia and a fluctuation of visual acuity which will certainly disappear within a variable amount of time (from 10 to 60 days, in our statistics).
At this point we have compared the Symmetric Radial Keratotomy developed by Prof. Fyodorov and the asymmetric Radial Keratotomy conceived and developed by Prof. Massimo Lombardi. The comparison consists of:
Radial Keratotomy
1) Marking of the optical zone with markers of a diameter from 3.2 mm to 5.5 mm.
2) Marking of the cornea with markers provided with a number of radials from 4 to 12.
3) Eventual addition of radial or tangential incisions for the correction of the astigmatism.
4) Incision of the corneal stroma along the direction of the radial marks.
5) Deepening the incisions in order to incise the stroma as deeply as possible (90%).
Asymmetric Radial Keratotomy
la) In A.R.K., we never go below the 4.0 optical Zone: normally from 4.0 to 5.5
2a) In A.R.K., the incisions (1 to 10) are done only in one sector from 30° to 270° (in most cases).
3a) This is usually done in A.R.K.
4a) No change in A.R.K.
5a) In A.R.K. normally from 70% - 80%. Not more!
For the majority of the cases, total correction was obtained after the first operation of A.R.K. and allowed the patients to avoid using corneal lenses, whose excessive use is one of the main reasons for the worsening of the keratoconus. It was possible to correct the eventual residual ametropia with eyeglasses, attaining in most of the patients a satisfactory utilization which was impossible before surgery.
Discussion
After 9 years of successful experience with this technique patients and following a scrupulous supervision of the patients for the stability of the ophthalmometry and the pachymetry, we can conclude by suggesting that A.R.K. should be considered as the elective surgical treatment of type I, II and selected cases III keratoconus.
And the sooner the better!!
Patients presenting bilateral keratoconus always chose to operate on the second eye. This proves to be an improvement due to a subjective appreciation. We believe that A.R.K. is not a "Panacea", but an effective surgical praesidium for accurately selected type I, II and III keratoconus patients.
This technique does not interfere with other eventual surgical praesidia such as myopic or aphakic epikeratoprothesis, corneal transplant, cataract plus I.O.L. implantation, glaucoma or retinal and vitreous surgery, etc.
The explanation of the clinical results could be the following:
1) the flattened corneal profile obtained with A.R.K. normally eliminating the corneal ectasia, allows a more regular distribution of pressure into the Anterior Chamber;
2) the gradual healing of the incisions, obtained by a tissue rich with fibrin, creates a new organic net with a great capacity of structural support directly in the corneal stroma, which was tectonically thinner and weaker. This structural support avoids a relapse of the original defect in the future.
Prof. Fyodorov formulated in his previous works some similar ideas regarding the healing of Radial Keratotomy incisions and his theory is supported by a wealth of cytological and histological examinations, and by optic, electronic and scanning microscopy.
Obviously the healing of incisions on a cornea affected by keratoconus needs more time.
Our convictions were based on these two points:
1) after nine years from the first operation we observed that one case out of 48 presented signs of ectasia; as for this only patient, we have to say that she is a female patient and together with keratoconus worsening she had an organic wasting which could explain this case.
2) a regular pachymetric examination has demonstrated long term constant stability and normally an increase of about 20-30 μ of the corneal thickness. The group of patients with type I, II and III keratoconus up to the present have not required undergoing a penetrating keratoplasty or epikeratoprothesis (according to our statistics, not one of 48 patients during the 9 years of follow up).
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