The Intacs intrastromal ring segments have been demonstrated to cause corneal flattening in keratoconus.[2, 5, 6, 22, 35, 38, 39]. The change in spherical equivalent and keratometry have been significant and about 80% of eyes achieve an improvement in uncorrected and best corrected visual acuity[6, 20].

Collagen cross linking has been shown to slow and in some cases reverse the progression of keratoconus[40, 41]. Chan et al has published a small retrospective series on the use of cross-linking with Intacs insertion[42]. This is the first prospective study looking at the sequential effect of collagen cross-linking on patients who have had Intacs insertion. It is also the first study looking at the effect of Intacs on contrast sensitivity.

Methods

Ethics approval was obtained prior to recruitment of 50 patients from the South East Area Health Ethics Committee. All patients received fully informed consent. Patients were treated initially with Intacs and 6 months later collagen cross linking was performed. Preoperatively and at 1, 3 and 6 months after the insertion of the Intacs an intensive examination and visual assessment was performed.

Examination included uncorrected visual acuity, best corrected visual acuity, Pelli-Robson contrast sensitivity, Orbscan II corneal topography and a full eye examination. A validated quality of vision questionnaire was we had developed for assessing of visual function after refractive surgery was used to assess the patients perception of their own visual function[43]

The surgical procedure was performed under sterile conditions. The Intralase femtosecond laser (AMO IntraLase Corporation, Irvine California) was used to create the channels. A decision based on the location of the cone determined whether 1 or Intacs segments were inserted. In decentred cones 1 was inserted and for central cones 2 were inserted. The incision corresponded with the steep axis on manifest refraction.

Background and Literature Review

The Intrastromal Corneal Ring Segments (ICRS) are small semi-circular plastic segments which can be inserted into stromal channels in the mid-periphery of the cornea. The segments act as passive spacing elements and can shorten the arc length of the anterior corneal surface inducing flattening. ([1-3]. Whilst they were originally designed to treat low levels of myopia, they have been used successfully to treat keratoconus.[4-6]

The degree of shortening of the arc length and therefore the degree of flattening is proportional to the thickness of the insert in particular, but also the depth at which they are placed and the distance from the centre of the visual axis. [4, 7]

The aim of the ICRS has been to improve best spectacle corrected visual acuity or visual acuity with contact lenses. The major advantage of these devices over other treatment modalities for keratoconus is that they involve a relatively simple surgical procedure which is only moderately invasive and in most cases, is reversible. ICRS are manufactured by two medical device companies. The most commonly available in Australia and the United States is Intacs (Addition Technology Inc) and in Europe the Ferrara Intrastromal Corneal Ring Segments (Mediphacos) are available.

The Intacs are made from PMMA (Polymethyl Methacrylate) and come in segments between 0.25mm and 0.45mm with an arc length of 150 microns. The surgical procedure can be performed utilising a surgical device which involves stromal separation of the corneal lamellar at a fixed depth or, more commonly these days, with the IntraLase femtosecond laser. [4, 8] All patients in this study had channel creation utilised by the IntraLase femtosecond device.

The IntraLase is capable of not only creating the stromal channel at a pre-determined depth but can also create the side incision through which the ICRS are inserted. Sutures can be used to close the 1.4mm incision but were not used in any of the patients in this study.

The Ferrara ring segments are made of an acrylic perspex (CQ) and differ from the Intacs in that they have triangular cross section. There is significantly less information about these devices in the peer reviewed literature.[9, 10]

The ICRS were originally developed for the treatment of mild myopia but their lack of predictability has made this indication redundant [11] The ICRS have been used for keratoconus, iatrogenic corneal ectasia and pellucid marginal degeneration.[9, 12-19] The body of evidence supporting the use of intracorneal stromal rings is relatively sparse.

What are Intrastromal Corneal Ring Segments?

The Intrastromal Corneal Ring Segments (ICRS) are small semi-circular plastic segments which can be inserted into stromal channels in the mid-periphery of the cornea. The segments act as passive spacing elements and can shorten the arc length of the anterior corneal surface inducing flattening. ([1-3]. Whilst they were originally designed to treat low levels of myopia, they have been used successfully to treat keratoconus.[4-6]

The degree of shortening of the arc length and therefore the degree of flattening is proportional to the thickness of the insert in particular, but also the depth at which they are placed and the distance from the centre of the visual axis. [4, 7]

The aim of the ICRS has been to improve best spectacle corrected visual acuity or visual acuity with contact lenses. The major advantage of these devices over other treatment modalities for keratoconus is that they involve a relatively simple surgical procedure which is only moderately invasive and in most cases, is reversible. ICRS are manufactured by two medical device companies. The most commonly available in Australia and the United States is Intacs (Addition Technology Inc) and in Europe the Ferrara Intrastromal Corneal Ring Segments (Mediphacos) are available.

Intacs

The Intacs are made from PMMA (Polymethyl Methacrylate) and come in segments between 0.25mm and 0.45mm with an arc length of 150 microns. The surgical procedure can be performed utilising a surgical device which involves stromal separation of the corneal lamellar at a fixed depth or, more commonly these days, with the IntraLase femtosecond laser. [4, 8] All patients in this study had channel creation utilised by the IntraLase femtosecond device.

The IntraLase is capable of not only creating the stromal channel at a pre-determined depth but can also create the side incision through which the ICRS are inserted. Sutures can be used to close the 1.4mm incision but were not used in any of the patients in this study.

The Ferrara ring segments are made of an acrylic perspex (CQ) and differ from the Intacs in that they have triangular cross section. There is significantly less information about these devices in the peer reviewed literature.[9, 10]

The ICRS were originally developed for the treatment of mild myopia but their lack of predictability has made this indication redundant [11] The ICRS have been used for keratoconus, iatrogenic corneal ectasia and pellucid marginal degeneration.[9, 12-19] The body of evidence supporting the use of intracorneal stromal rings is relatively sparse.

Studies

This body of evidence is relatively sparse and according to the NH & MRC classification for dimensions of evidence (NH & MRC 2000) presents only a grade 4/4 evidence level. The maximum total number of keratoconic eyes treated, that have been recorded in published series less than 1000, although this number is somewhat uncertain as there is likely to be some overlap in the studies produced by the same author. With regards iatrogenic corneal ectasia there are probably only in the order of 30 – 50 eyes in the studies published and non-iatrogenic corneal ectasia (pellucid marginal degeneration) , around 20 eyes.

Most studies have concentrated on improvement in visual acuity, astigmatism and keratrometry. In assessing visual function, the mean best corrected visual acuity when measured in Logmar improved in all studies.

Mean uncorrected visual acuity improved in all studies in which it was reported. The lines gained varied from 3-6.[2, 5, 22] Other groups reported the % of eyes which had an improvement in uncorrected visual acuity and this was relatively stable at around 80%. [6, 9, 10, 20]

The mean post-operative best corrected visual acuity improved by 0.2 Logmar to 0.4 Logmar in many of the studies of keratoconus [2, 29] [9, 24, 30] and a similar improvement was found in the four studies of the iatrogenic corneal ectasia [18, 19, 25] [31]. For keratoconic patients a gain of between 1 – 8 lines was reported for between 45% – 88% of eyes (median 67%) but no change was reported for between 2% – 51% (median 20%) and a loss of at least one line of best corrected visual acuity occurred between 0% – 15% (median 8%). Some studies recorded the improvement in terms of % of eyes that improved. This ranged from 59-86.4%.[6, 10, 20]

The mean uncorrected visual acuity in Logmar improved in all studies. The mean post-operative uncorrected visual acuity ranged from 0.33 Logmar to 0.74 Logmar in five studies of keratoconus ([2, 9, 24, 29, 30] and from 0.32 Logmar to 0.52 Logmar in the four studies of iatrogenic corneal ectasia [18, 25, 31, 32]. The mean change for keratoconic patients ranged from 2 – 6.5 lines of improvement in uncorrected visual acuity in the four studies [2] [24, 33] and from 4 – 10 lines for the small number of cases represented in the iatrogenic corneal ectasia. Overall 70% – 80% of eyes had a gain of 1 or more lines of best spectacle corrected visual acuity but around 5% experienced a loss of best spectacle corrected visual acuity.

Refractive Cylinder

All other studies that bothered to report the change in refractive cylinder have demonstrated a reduction. The mean reduction in keratoconic has been between 1.3 and 2.7 dioptres. Few studies took in to account wither vector analysis or keratometric astigmatism.

Spherical Equivalent

All other studies demonstrated a reduction in post-operative spherical equivalent. The mean reduction in spherical equivalent ranged from 1.4 to 5.7 dioptres in the keratoconic studies

Keratometry Studies

Keratometry was similarly reduced post-operatively in all studies in which it was reported. The mean reduction in keratometry post-operatively ranged from 3.3 dioptres to 8.5 dioptres at between 6 and 24 months post-operatively in seven of the studies[5, 6, 9, 10, 20, 23, 24, 29, 33, 34]

Complications

Complications with use of Intacs can be divided into intraoperative and post-operative. The main intraoperative complication that occurred was that the Intacs could not be inserted in 8% of some series [23]. Intraoperative perforation was also reported[35]. The majority of series reported no intraoperative complications[5, 6, 20, 23].

The rate of post-operative complications depended on definitions and ranged from 3% – 39% [2, 9, 10, 24, 29]. The observation of lamellar channel deposits at the edge of the ICRS with small amounts of epithelial in-growth were observed but not considered in any series to be a significant complication. Hofling-Lima 2004 [36] reported a culture proving case of infectious keratitis in seven eyes with seven patients who received Ferrara ICRS. Zare also reported a case of bacterial keratitis[5] A seemingly disproportionate number of the reported cases of bacterial keratitis occurred in the series using Ferrara rings with two patients requiring penetrating keratoplasty.[10, 30]

Shehadeh-Masha-Our (2004)[37] reported one case of patient who had Intacs insertion for iatrogenic corneal ectasia and developed an infection that resulted in loss of best corrected visual acuity. Explantations occurred between 4% – 25% with a median of 9% in nine studies [2, 9, 10, 24, 29, 33, 34]. The most common reason for explantation was dissatisfaction with visual quality. A segment extrusion or decentration was also a reason for explanation. Chronic foreign body sensation or incorrect placements were other reasons given for explanation. In Colin’s European study 2006 12% of eyes underwent removal of the Intacs due to dissatisfaction with the visual outcome.[33]

Methods Continued

The surgery was centred on the centre of the entrance pupil with consideration to the apex of the cone. Patients were pretreated with Valium 5mg, Minims BNX (Oxybuprocaine Hydrochloride 0.4%,Chauvin Pharmaceuticals, England), Ciloxan 0.3% (Ciproflaxacin, Alcon Laboratories, Fort Worth, TX, USA) and Voltaren Ophtha 0.1% (Diclofenac Sodium 1mg/ml, Novartis Pharmaceuticals) After insertion of the Intacs, Ciloxan and Maxidex was used four times per day for one week following surgery. At one week Ciloxan was ceased however Maxidex was continued twice a day for a further 3 weeks. Voltaren Optha was also used three times per day for the first week after surgery and twice a day for a further week.
Patients were reviewed the next day, 1 week, 1 month 3 months and 6 months.

Six months after Intacs insertion, collagen cross linking was performed. The technique was performed in accordance with the protocol outlined by Wollensak. Briefly an 8mm area of the central epithelium was debrided after anaesthetizing the cornea. Riboflavin Vitamin B2 0.1% with Dextran 500 (Peschke Meditrade, Kiel, Germany) was administered every 5 minutes until there had been complete penetration of the cornea as evidenced by visibility in the anterior chamber on slit-lamp examination.

The eye was then exposed to ultraviolet light from the calibrated light source. (UV-X IROC AG, Zürich, Switzerland) for 30 minutes. Ciloxan 0.1% was administered immediately post surgery and a bandage contact lens (Night & Day, CIBA Vision Duluth, GA, USA) was placed on the eye. This was left in place for 4 days. Ciloxan and FML (Flourometholone 1mg/ml, Allergan Irvine, CA, USA) were prescribed four times per day in the treated eye for one week following surgery.

Postoperative reviews were carried out at Day 1, Day 4, 1 Month and 3 Months.