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SACL and Mini ASRK
Introduction
Keratokonus is one of the most deeply investigated degenerative diseases of the cornea in the current ophthalmological scene. Cross Linking is minimally invasive treatment that is practised worldwide to reduce and stop keratoconus in the early phases of the disease. SACL (Selective Asymmetrical Cross Linking) is non invasive treatment, which seems to produce a better outcome by compacting collagen’s helical structure with a mean refractive correction of 2 – 2,5 diopters, compared to the 1 -1,5 diopters achieved by the traditional Cross Linking method.
Mini ARK (Mini Asymmetrical Radial Keratotomy) is an incision-based microsurgery technique that, after a 24-year follow up, still remains the only one that obtains an “implosive” effect with compacting of the corneal stroma, which is both lengthened and proportionately thinned by keratoconus.
Mini SARK (Mini Selective Radial Keratotomy) combines the latest innovative changes that have further improved the well tested Mini ARK method (Mini Asymmetrical Radial Keratotomy) by selectively reducing the operated surface. This has been achieved by introducing new concepts that further limit the sector, which is mapped out for surgery, and by using a method that minimises the number and length of incisions made, thus better linking transition areas to both enhance compacting of the corneal stroma and to make the treated surface’s overall regularisation more harmonious.
Mini SARK also ensures better refractive correction of ametropia caused by keratoconus. This method is currently applied prior to SACL (Selective Asymmetrical Cross Linking) treatment.
Materials and methods
Our study was conducted on a sample of 200 eyes with patients belonging to both sexes (100 males and 70 females) and aged between 20 and 50 years, divided as described below:
- n° 15 eyes treated only with SACL without the Mini SARK method;
- n° 20 eyes operated with the Mini SARK method and submitted to SACL treatment during the same session;
- n° 40 eyes operated with the Mini ARK method and submitted to SACL treatment at different time intervals;
- n° 125 eyes operated with the Mini ARK method
Chart 1: Patient Subdivision
Patients were monitored over a 6-month observation period with the follow ups listed below:
- the first within 15 – 20 days following either treatment or surgery plus treatment;
- the second after 2 months;
- the third after 4 months;
- the fourth and last one on the sixth month.
Inclusion criteria for SACL treatment
- Patient with clinically confirmed keratoconus documented by diagnostic investigations.
- Patients with corneal thickness that either meets requirements or can be centrally increased to at least 400 microns before commencing UV-A treatment. Corneal thickness must be measured with an electronic pachymeter.
- Patient, whose cornea is sufficiently transparent in the central and paracentral regions (specifically, patient with corneal leukomas that do not concern the visual axis).
- Patients already operated with the Mini ARK method or concurrently submitted to Mini SARK surgery, who have, anyhow, reached the condition specified in point 2.
- Patients who have undersigned the specific Informed Consent Form, as required.
Exclusion criteria
- Patients, whose corneal thickness either differs from 400 micron or has been brought to the said thickness, before commencing treatment.
- Patients with either herpetic keratitis or active eye infections.
- Patients with a serious dry eye syndrome.
- Patients with serious central scars that inhibit sight
Screening patients for SACL treatment
a) Patients who cannot be treated otherwise.
b) Patients operated with the Mini SARK method and immediately submitted to SACL treatment during the same session.
c) Patients already submitted to previous Mini ARK surgery.
Differences between the two methods: SACL and traditional cross linking
SACL differs from traditional Cross Linking due to the following changes[1]:
- it does NOT remove the epithelium;
- it has a “selective asymmetrical” mode of implementation, both in SACL treatment and in concurrent microsurgery, if any;
- SACL can be performed on corneas that have, anyhow, reached 400 microns (ascertained with the electronic pachymeter) before treatment commences; we too have established this value as minimum thickness required to guarantee treatment free of undesired harmful side effects; many patients reached this minimum pachymetric value by inducing artificial oedema prior to treatment by repeatedly using anaesthetic eyewashes, riboflavin and vitamin C for a prolonged period;
- it makes use of corneal lenses that act as masks to restrict treatment only to desired area;
- it requires maximum myosis during treatment.
Treatment “ratio”
A mechanism that, like Cross Linking, hardens and thickens collagen fibres had already been detected in the faster and higher degree of corneal aging (i.e. physiological) in individuals intensively exposed to natural UV-A rays (i.e. sailors and mountain climbers). WE can, hence, consider the existence of occupation and age-related physiological Cross Linking and of “photobiologically” induced therapeutic Cross Linking.
SACL (Selective Asymmetrical Cross Linking) and the traditional Cross Linking method encourage photopolymerisation of stromal collagen fibrils to enhance stiffness and resistance to progressive keratoectasia.
This is implemented by the combined action of a photosensitive agent (i.e. either riboflavin of vitamin B2 plus vitamin C) and a photoabsorbent substance that is evenly irradiated with UV-A (with 320-400nm wavelength, 3mW/cm² power on a 10mm diameter and, at a height of approx. 3cm form the corneal apex) on a diameter of approx. 1cm.
Moreover, this method, which combines riboflavin-UV-A and vitamin C, is technically simpler and less invasive thatn all other therapeutic and surgical options for keratoconus.
Cross Linking focuses on preventing and treating some of the most important physiological and pathological processes that cause keratoconus and which have already proved the following in the traditional mode:
- enhanced corneal resistance and biomechanical stability;
- increased effect on collagen fibril diameter, followed by cell repopulation that starts from the deep corneal layers (whose cells are whole)
This repopulating process lasts less than the Cross Linking phenomenon reported by colleagues in Dresden, since the latter is much higher than the collagen renewal time, which requires 24-36 months for completion. Collagen Cross Linking with riboflavin is currently recommended for forms of keratoconus during the refractive phase (stage 1 and 2), whose negative progress and worsening over the past 6 months can be clinically, topographically and pachymetrically documented.
The SACL method does not categorically exclude corneas, whose central pachymetric value is below 400 microns, since corneal thickness can often be increased to the required thickness, while preparing for SACL treatment. Various authors, numbering Prof. Theo Seiler, have adopted this method, obtaining the same results as treatment administered for thicker corneas.
We must also consider that during the performance of the incision, the cornea becomes edematous and increases by 100 – 150 microns, thus enabling SACL treatment to be administered to a sample population presenting a wider pachymetric range.
SACL masks
To make the most of this technique, we used masks made of either semirigid or rigid lenses (patent pending) and, specially designed to (asymmetrically) use SACL treatment for keratoconus, specifically on the ectasic area defined by the map prior to treatment.
These masks are also used for cases that previously undergone either Mini ARK micro-incisions of concurrent Mini-SARK surgery.
90° 120° 180° 210°
Chart 2: UV-A Treatment Masks
In fact, these masks, which allow the penetration of UV-A rays, start from 90°, which is the treated sector in initial cases or, however, in keratoconus types 1 and 2; they subsequently increase by a 30° angle for advanced keratoconus. These lenses are, therefore, 120°, 150°, 180° and 210°, to allow correct exposure to UV-A treatment.
They have a 12 mm diameter to easily adhere to the bulbar conjunctiva; they are black and leave only the 7,5 mm sector to be treated open. The use of these special lenses (patent pending) enables us to:
- understand (implying that the flattening effect of Cross Linking is achieved on the entire corneal tissue, as occurs to date with the traditional method) that flattening of the blue sector on the corneal map (where the cornea is normal) induces a “balancing” effect with subsequent lesser flattening in the yellow-red ectasic region;
- limit UV-A exposure only to sick parts - which are ectasic (normally yellow –red on the corneal map) with sectors that have a progressive width and whose surface extension and position resembles the image of the ectasic area on the map – by complying with their asymmetry and by darkening the healthy tissue area to only expose sick tissue.
The disease’s asymmetry is the reason why, 24 years ago, the author first conceived ARK surgery followed by Mini ARK surgery, as the only techniques that could, to date, regularise, remould, compact and improve the asymmetrical unevenness of the cornea’s anterior surface.
Chart 3: Comparative graphics of K, CL, CLAS
Definition of the surgical aspect
In Asymmetrical Radial Keratotomy, which is used to correct and implode the keratoconus, 1,5-2 mm. long micro-incisions are made with a diamond-tipped scalpel.
They are generally only performed on the extroverted corneal region, outside the field of the pupil, with approx. 30° increases, from 90° to 270°. In 98% of cases, correctly performed “Asymmetric Radial Keratotomy” is decisive for keratoconus, both to stop the disease and for refractive functional recovery, which is recovery of sight. This surgery is performed under local anaesthesia in the outpatients’ clinic, and requires no bandaging. It lasts approx. 1-3 minutes per eye and ensures instant good results at the end of surgery.
Few cases are required to use sunglasses for a few days. Special eyewashes are then prescribed for about 7 days after surgery.
Discussion on Effectiveness
The concept of “Asymmetrical Selective Treatment” has been equally applied to Cross Linking too, for two reasons:
1) It is pointless attempting to flatten an area that is already refractively flat or, whose curvature radii are normal, as usually occurs in the initial stages on the corneal map, in the area opposite the ectasic one;
2) It exploits incisions present at the end of Mini SARK surgery and, without removing the epithelium, enhances penetration of vitamins B2 and C through the same incisions that convey the drug to the deepest layers (thickness) of stromal collagen. Moreover, the use of masks restricts UV-A irradiation to the ectasic zone, enhancing the possibility of re-establishing initial curvature radii (those prior to the disease) or, however, of reducing curvature radii to ensure better regularisation of the cornea’s ectasic surface. It is clear that the concept of Mini SARK surgery also applies to SACL treatment: “SOONER THE BETTER”, because strengthening the corneal collagen by means of SACL-related photopolymerisation and/or with cicatrisation rich in fibrin induced by the mini-incisions of Mini-SARK surgery, have both the same rationale and preventive goal concerning the disease’s further progress. It thus concretises the chance of a clear improvement, as proved to date, obtaining curvature radii that are closer to those present prior to the disease, “because the entity of corneal deformation is only initial” (keratoconus type 1 and 2). This insight has been confirmed by clinical results, which prove the higher degree of regularisation with corresponding enhanced flattening of the central and paracentral optic zone. It reduces astigmatism and produces a refractive improvement that is far higher than 1.5-2 diopters (reported by literature for the traditional Cross Linking mode) and, which can reach an average of 2-2.5 diopters in cases treated solely with our SACL method and, at least 3-5 additional dioptres with combined Mini SARK treatment.
This paper is designed to clearly define some concepts that we consider more adherent to the condition of dystrophic change of corneal stroma and subsequent secondary ectasia, with the asymmetry resulting from the biomechanical and anatomical alterations caused by keratoconus. We have observed relatively positive results by treating the ENTIRE CORNEAL SURFACE (360°) with riboflavin and, then irradiating it with UV-A, since dystrophic, malacic and ectasic events that characterise the disease generally concern only one “part”, or rather “sector”, of the cornea, especially in the initial stages of keratoconus, which are the method’s target.
The rational is as described: if a technique that can create an effect of coarctation of the elastic proteins of collagen is applied on the entire corneal surface, only a relatively uniform flattening effect will be achieved all round. This occurs because the symmetrical treatment enhances the difference between the ectasic area and the one with normal curvature, with subsequent partial regularisation (of the surface of the keratoconus) in the ectasic area (Weighing Scale Effect).
SACL (Selective Asymmetrical Cross Linking) Treatment Procedure
1) Perform a pre-operative check of the pupil’s myosis that is increased to at least 1.5-2 mm, also through the preventive use of “Gonioplastic Argon laser” wherever anomalous iridocorneal adherences at the corner prevent intense myosis.
2) Administer ½% Pilocarpin eye-wash: 2 drops 1-2 times, 15-30 minutes prior to treatment.
3) Perform local anaesthesia with either 4% Lidocaine eyewash or 0.4% Benoxinate Chloride, 2 drops 6-10 times, 20-30 minutes prior to treatment.
4) Position the blepharostat.
5) WITHOUT REMOVING THE EPITHELIUM, administer 4-5 drops of riboflavin (0.1% phosphate = vitamin B2) plus vitamin C every 3-5 minutes, 20-30 minutes prior to irradiation with UV-A (ultraviolet).
6) Use the electronic pachymeter during the preparation phase, before irradiation with UV-A, to ascertain that the minimum central corneal thickness of 400 microns has been reached.
7) Apply corneal lenses to the mask at 90°-210° on the sector designed for the disease’s stage-specific treatment.
8) Start corneal irradiation with UV-A for a theoretical diameter of 9-10 mm at the centre of the cornea.
9) Administer riboflavin and vitamin C drops every 3-5 minutes during the entire treatment period.
10)30-minute exposure to UV-A rays
11)Wash the corneal surface with physiological solution and, finally medicate with Tobral or Tobradex antibiotic eyewash.
Comparing methods
Advantages of the sole administration of SACL treatment
- Conservative non invasive treatment of keratoconus with rapid 24-hour functinal recovery in 85% of cases and, within at most 5 days in the remaining 15 %.
- Statistically, the treatment almost always stops or slows down the progress of keratoconus. It also further reduces the corneal curvature achieved, compared to traditional Cross Linking and, it can be reasonably deemed a method that has an adequate capacity of preventing most corneal transplantations.
Advantages of combining SACL treatment and Mini SARK surgery
- The combination of the two techniques, despite the scarce but different invasiveness of Mini SARK surgery, is, as confirmed by our study's clinical results, an improvement, compared to either method applied individually.
- Hence, the two methods will have a greater “preventive” function in preventing this progressive degeneration from leading to the need for corneal transplantation.
Comment-summary
This paper focuses on the concept of “SELECTIVE ASYMMETRICAL TREATMENT” either for SACL treatment alone or combined with Mini SARK microsurgery, since both contemplate reducing ectasia and either partly or totally correcting the related spheroastigmatic myopic ametropia. 23 years of continuously using asymmetrical incisional microsurgery (Mini ARK) are proof of our belief in the need to intervene respecting “the asymmetry of corneal deformation”; hence, the “treatment focused on only correcting the deformation” and on restoring normal curvature radii, as far as possible. The use of traditional Cross Linking has revealed the possibility of reasonably reducing corneal curvature by approx.1-1.5 diopters. It can also reasonably reduce, and even prevent, the need for corneal transplantation, since, to date, this technique has no contraindications for subsequent treatment.
A patient can therefore be treated again at time intervals yet to be defined. This Centre performs SACL treatment with highly satisfactory and promising results and a 2-3 diopter reduction in corneal curvature, which involves better refraction, compared to the traditional method.
We also use SACL either concurrently or after Mini SARK surgery with decidedly better results that are more stable in time. Speaking in COLOURIMETRIC-ALTIMETRIC MAPPING TERMS, it is clear that to regularise tissue that is either partly or asymmetrically ectasic due to disease, we must only treat the area that is first yellow and then red (“hilly”) on the map, and not the remaining opposite surface that is blue on the map (“level”), which in the keratometric scale usually indicates a normal curvature radius, that is at times even under average, hence, flatter than normal.
Chart 4: Corneal map
Hence, we have designed a method that respects flat tissue by only focusing on changes and, therefore, on levelling the ectasic surface (diseased) that is initially yellow and, then red on the map.
Conclusion
Concluding, “THE IDEA IS SIMPLE AND, AS SUCH, HAS PROVED EFFECTIVE”, justas the Mini ARK method previously proved simple and effective, enabling us, through the concurrent use of both techniques, to double the flattening effect and, hence, the related dioptric correction of ametropia resulting from keratoconus. We have thus obtained 2-3 diopter variations only with SACL and, even 3-5 diopters with combined SACL and Mini SARK surgery.
Compliance
The higher degree of satisfaction shown by patients at the end of either treatment or surgery combined with treatment, has been further confirmed over the following months, strengthening our belief in the efficacy of changes made to the Cross Linking method and, in the further increase in efficacy achieved by combining the two techniques (increased compliance).
Chart 5: Results of work
Chart 6: Results of work
[1] We could say that we have used the SACL method either with or without associating it with the Mini SARK surgery, even on other diseases involving the ectasic degeneration of corneal tissue (i.e. pellucid degeneration), on patients who have undergone operations with INTACS and Ferrara-Rings techniques, Laser-Keratectomy for excimers on the corneal apex and, on patients submitted to RK and corneal transplantation. These cases will be discussed in other papers.
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