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Year : 2013  |  Volume : 20  |  Issue : 1  |  Page : 46-50  

Efficacy and safety of intacs SK in moderate to severe keratoconus

1 Department of Ophthalmology, Faculty of Medicine, Ain Shams University Egypt; International Medical Center, Dubai, United Arab Emirates
2 Department of Opththalmology, Magrabi Eye Hospitals, Saudi Arabia

Date of Web Publication23-Jan-2013

Correspondence Address:
Ahmed M El-Moatassem Kotb
Department of Ophthalmology, Ain-Shams university, Abbasyia square, Cairo, Egypt, 46 Dr. Ahmed Mohamed Ibrahim street, Nasr city, Cairo, Egypt 11471

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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0974-9233.106386

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Purpose: To examine the safety and efficacy of Intacs SK for moderate to severe keratoconus (KC) using femtosecond technology.
Materials and Methods: This prospective, non-comparative study included 37 contact lens intolerant keratoconic eyes (stage II-III) of 24 patients who underwent femtosecond-assisted Intacs SK implantation. Inclusion criteria were mean K readings <56.00 D, corneal thickness >400 μm at the incision site, mesopic pupil <6.50 mm. Evaluation included manifest refraction, slitlamp examination, corneal topography, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA). P < 0.05 was statistically significant.
Results: Thirty-one (83.8%) eyes were classified as Amsler-Krumeich's stage II and 6 (16.2%) were stage III. Mean central pachymetry was 490.3 ± 37.4 μm. UDVA at 6 months post-operatively was significantly better than pre-operatively (0.90 log MAR ± 0.52 standard deviation [SD] versus 0.32 ± 0.27 logMAR; respectively, P < 0.0001), as was the spherical equivalent (SEq) (-3.64 ± 2.52 D vs. -1.84 ± 2.2 D; P < 0.0001). The mean CDVA and manifest cylinder improved compared with pre-operatively (P = 0.319 and P = 0.078, respectively). Average keratometry decreased significantly from 48.50 ± 3.08 D to 44.40 ± 3.03 D (P < 0.0001).
Conclusion: Implantation of Intacs SK using femtosecond laser in moderate to severe KC is safe and effective.

Keywords: Intacs, Intralase, Keratoconus

How to cite this article:
El-Moatassem Kotb AM, Hantera M. Efficacy and safety of intacs SK in moderate to severe keratoconus. Middle East Afr J Ophthalmol 2013;20:46-50

How to cite this URL:
El-Moatassem Kotb AM, Hantera M. Efficacy and safety of intacs SK in moderate to severe keratoconus. Middle East Afr J Ophthalmol [serial online] 2013 [cited 2022 Aug 11];20:46-50. Available from: http://www.meajo.org/text.asp?2013/20/1/46/106386

   Introduction Top

Keratoconus is a bilateral, non-inflammatory, and progressive corneal ectasia that can decrease visual acuity by stromal thinning, irregularity, and paracentral steepening. [1] Refractive management of early stages of keratoconus (KC) includes the use of spectacles or contact lenses. [2] However, disease progression can result in contact lens intolerance. [2],[3] After the introduction of the intrastromal corneal ring segment, Intacs (Addition Technology Inc., Des Plaines, IL, USA) in 2000 for KC, [4] they has emerged as the mainstay of refractive management of contact lens intolerant keratoconic eyes with clear central corneas. [3],[4],[5],[6],[7],[8],[9],[10],[11]

Recently, Intacs SK was introduced with two significant design modifications - a smaller inner diameter of 6.0 mm compared to 6.8 mm of the standard Intacs; and an elliptical cross-section compared to a hexagonal cross-section of the standard Intacs. [11] Although the smaller diameter of Intacs SK was introduced to better address the higher refractive errors associated with the more severe forms of corneal ectasia, the smaller diameter of 6.0 mm with appropriate thickness also has a potential to achieve superior anatomical and refractive outcomes in the earlier stages of KC. Therefore, Intacs SK has been introduced in smaller thicknesses to manage the lower refractive error associated with early KC.

While there are two studies evaluating the implantation of Intacs SK for the treatment of severe KC, there is no such publication on Intacs SK in moderate and severe stages of KC. [12],[13] Sansanayudh et al. [12] evaluated the outcome of Intacs SK implantation in 10 eyes of advanced KC and found a statistically significant improvement in visual and aberrometric outcome in 6 months. However, the improvement in refractive parameters were not statistically significant. Kamburoglu et al. [14] presented the results of their comparative study between Intacs SK and Intacs implantation in patients with advanced KC at the 12 th European society of cataract and refractive surgery (ESCRS) Winter Refractive Surgery Meeting and Cornea Day and concluded that refractive results and K readings had improved in Intacs SK implanted eyes compared to standard Intacs.

Patients in the Middle East represent an excellent potential study cohort for KC related studies. This is due to the high prevalence of KC with contact lens intolerance as a result of baseline discomfort associated with the dry and dusty environment and the high prevalence of vernal keratoconjunctivitis which often precludes contact lens tolerance. [15],[16] In this study, we examine the safety and efficacy of the use of Intacs SK in moderate to severe stages of KC.

   Materials and Methods Top

This prospective non-comparative study included 37 consecutive keratoconic eyes of 24 patients who underwent Intacs SK implantation (Addition Technology Inc., Des Plaines, IL, USA) between June 2009 and September 2010. All implantations were performed using femtosecond laser (Intralase FS60, AMO Inc. USA) by a single surgeon (A.K) at a single center International Medical center (IMC) , Dubai, UAE . The risks, benefits and alternatives to the treatment were thoroughly explained to the patients prior to the surgery and written informed consent was obtained from all patients. Institutional Review Board approval was obtained prior to the study.

Inclusion and exclusion criteria

Inclusion criteria were stage II-III keratoconic eyes based on Amsler-Krumeich's classification, mean K readings <56.00 D, corneal thickness >400 μm at the incision site, mesopic pupil <6.50 mm and contact lens intolerance to rigid gas permeable lenses. Exclusion criteria were eyes with advanced KC, severe dry eye, cones with striae or central scarring. Keratoectasias due to pellucid marginal degeneration were excluded. Additionally, patients who were unlikely to be available for regular follow-ups or had previous interventions, such as LASIK or cross linking, were excluded. Patients having intractable itching despite the maximum tolerable medication were also excluded as they were expected to continue eye rubbing post-operatively. One eye of each patient was selected randomly.

Study parameters included manifest refraction, slit lamp examination, corneal topography (Allegretto Wavelight Topolyzer, WaveLight Laser Technologie AG, Germany), uncorrected distance visual acuity (UDVA) and, corrected distance visual acuity (CDVA) using a Snellen chart and converted to logMAR for analysis. Ultrasound pachymetry (SP-3000, Tomey Corp., Nagoya, Japan) was used to measure the peripheral and central corneal thickness. Follow-up was scheduled on 1, 7 th day and then on 1, 3 and 6 months.

Surgical nomogram

Eyes with cones centered on corneal topography were implanted with symmetric Intacs ring segments, as recommended in the manufacturer's nomogram. Eyes with decentered cones were implanted with two asymmetric segments.

The selection of the segment size was based on the spherical equivalent (SEq) in symmetric implantations and on the cylinder power in asymmetric eyes [Table 1] and [Table 2]. The site of incision was determined according to the positive cylinder axis, if it was within 10° from the steep keratometric meridian on corneal topography. In cases of axis discrepancy of more than 10° between the positive cylinder axis and steep keratometric meridian, incisions were placed perpendicular to the peripheral flattening, as seen on the axial topography.
Table 1: Surgical nomorgam of Intacs SK

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Table 2: Femtosecond parameters (Intralase FS60, AMO Inc 1700 East St. Andrew PlaceSanta Ana, CA 92705-4933 United States) for creating Intacs SK channels

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Surgical technique

A previously described standard surgical technique was used in all cases. [13] Just prior to surgery two drops of topical anesthesia (oxybupracaine 0.4%; Bausch & Lomb Inc., Rochester, NY, USA) was instilled in the eye. A femtosecond laser was used to create a 360° channel at a depth of 80% of the corneal thickness at the incision site up to a maximum of 400 μm. The incision was located on the steep axis with an inner and outer diameter of 6.00 and 7.00 mm, respectively [Table 2]. The energy delivered was 6 mJ. The segments were inserted and positioned into the channel under an excimer laser microscope. A 10-0 nylon suture was used to secure the incision and removed 2 months post-operatively. Dexamethasone sodium phosphate 0.1% drops and moxifloxacin hydrochloride 0.5% drops were administered for 2 weeks post-operatively.

Statistical analysis

The data was entered in an Excel spreadsheet (Microsoft Excel 2000, Microsoft Corp., Redmond, WA, USA) and Prism version 5.03 (Graphpad Software Inc, La Jolla, CA, USA.). Change in UDVA, CDVA, SEq, refractive cylinder, average K and difference between steep and flat keratometries from pre-operatively to 6 months post-operatively, were analyzed using Student's t-test. P values lesser than 0.05 were considered statistically significant. All patients (n = 37 eyes) completed the 6-month follow-up; however, two eyes of two patients, who underwent superior segment removal for hyperopic shift, were not included in the post-operative analysis (n = 35 eyes).

   Results Top

The study included 37 contact lens intolerant eyes due to moderate to severe KC (24 subjects [13 bilateral and 11 unilateral]). The mean age of the 13 men and 11 women was 25 years ± 6 years (range 17-36 years). Thirty-one (83.8%) eyes were stage II based on Amsler-Krumeich's criteria and 6 (16.21%) were stage III. Five eyes (13.5%) had central cones and 31 (83.8%) had decentered cones. Mean central pachymetry was 490.3 ± 37.4 (range, 392-585 μ).

Refractive and visual results

There was a statistically significant improvement in UDVA, and SEq [Figure 1]a and c. The mean UDVA statistically significantly improved from 0.90 ± 0.52 log MAR pre-operatively to 0.32 ± 0.27 log MAR (P < 0.0001). There was statistically significant decrease in SEq from -3.64 ± 2.52 D pre-operatively to -1.84 ± 2.2 D at 6 months post-operatively (P < 0.0001). While the mean log MAR CDVA improved to 0.27 ± 0.24 from pre-operative values of 0.33 ± 0.37 log MAR, the improvement was not statistically significant P = 0.319 [Figure 1]b. Similarly, at post-operative 6 months, manifest cylinder had reduced from pre-operative -3.24 ± 1.68 D to post-operative -2.8 ± 1.65 D; the difference was not statistically significant P = 0.078 [Figure 1]d.
Figure 1: Visual, refractive, and keratometric outcomes following implantation with Intacs SK in mild to moderate keratoconus

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Keratometric changes

There was a significant reduction in the average K from pre-operative 48.50 ± 3.08 D to 44.40 ± 3.03 D at post-operative 6 months [Figure 1]e (P < 0.0001). However, the keratometric difference did not show a statistically significant change [Figure 1]f.

Intra and post-operative complications

All surgeries were uneventful. Two eyes (0.5%) developed bullous keratopathy at the wound site 2 weeks after the procedure and were successfully treated with tobramycin and dexamethasone combination eye drops (TobraDex® Ophthalmic Suspension, Alcon Laboratories, Inc.Fort Worth, Texas 76134 USA), administered 4 times a day for 2 weeks and for early suture removal.

Another two eyes of two patients (0.5%) developed hyperopic shift (overcorrection) and were successfully managed by removal of the superior segment 2 months after the primary surgery.

Overlapping of the distal ends of Intacs SK ring segments were noticed in two eyes of two patients (0.5%). Surgical adjustment was done followed by application of a single 10/0 nylon suture at incision site. The separated distal ends of the Intacs SK segments and the stitches were removed after 1 month from adjustment and no further migration were observed [Figure 2]a and b. Safety data in terms of change in CDVA is demonstrated in [Figure 3].
Figure 2: (a) Clinical image demonstrating overlap of distal ends. (b) Image following surgical correction of segments overlap

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Figure 3: Change in lines of corrected distance visual acuity from preoperative to 6 month postoperatively

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   Discussion Top

While Intacs SK has been documented to be of safe and effective in the advanced KC, [12] the aim of the current study was to evaluate the safety and efficacy of appropriate thicknesses of Intacs SK in moderate to severe KC using femtosecond assisted laser technology.

Thirty one (83.8%) eyes were of Amsler-Krumeich's stage II and had contact intolerance. The environmental factors play an important role in the tolerability of contact lens in arid environment of Arab Gulf countries. The contact lens intolerance in KC is believed to be due to two factors: (a) baseline discomfort associated with the dry and dusty environment, [15] which is further aggravated by the incessant air conditioning in residences, place of work and transportation and (b) high prevalence of vernal keratoconjunctivitis in the Middle East. [15],[16],[17]

In this study, 13 males and 11 females underwent Intacs SK implantation. Since KC is known to have no gender predilection, [1] such a gender difference is likely to be due to chance.

While there was a statistically significant improvement in UDVA, the improvement in CDVA was not statistically significant. We believe that this observation could be due to the reason that our study population had already a reasonable pre-operative CDVA.

Similar to the earlier reports of Intacs SK in advanced stages of corneal ectasias, [12] while there are recent reports of "no-intervention" approach to the overlapped distal edges of the standard Intacs segments, [18] we preferred to surgically address the overlapping Intacs SK segments as there is no safety data of the "no-intervention" approach for Intacs SK.

Our experience of using femtosecond laser to create the channels for Intacs SK in moderate to severe KC was safe with no intra-operative complications in our study. However, the small disadvantage of using femtosecond laser in the relatively thicker corneas of the moderate forms of KC is that the maximal channel depth of 400 μm is lesser than the recommended 75% depth in some thick corneas. However, none of our cases developed overlying stromal melt secondary to the elliptical cross section of Intacs SK.

Few potential limitations of our study are the short term follow-up duration of 6 months and lack of measurements of aberrometric changes.

We conclude that implantation of Intacs SK using femtosecond laser in moderate to severe KC is safe and effective using femtosecond assisted laser.

   References Top

1.Rabinowitz YS. Keratoconus. Surv Ophthalmol 1998;42:297-319.  Back to cited text no. 1
2.Jhanji V, Sharma N, Vajpayee RB. Management of keratoconus: Current scenario. Br J Ophthalmol 2011;95:1044-50.  Back to cited text no. 2
3.Colin J, Cochener B, Savary G, Malet F, Holmes-Higgin D. INTACS inserts for treating keratoconus: One-year results. Ophthalmology 2001;108:1409-14.  Back to cited text no. 3
4.Colin J, Cochener B, Savary G, Malet F. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg 2000;26:1117-22.  Back to cited text no. 4
5.Levinger S, Pokroy R. Keratoconus managed with intacs: One- year results. Arch Ophthalmol 2005;123:1308-14.  Back to cited text no. 5
6.Alió JL, Shabayek MH, Artola A. Intracorneal ring segments for keratoconus correction: Long-term follow-up. J Cataract Refract Surg 2006;32:978-85.  Back to cited text no. 6
7.Colin J. European clinical evaluation: Use of Intacs for the treatment of keratoconus. J Cataract Refract Surg 2006;32:747-55.  Back to cited text no. 7
8.Colin J, Malet FJ. Intacs for the correction of keratoconus: Two-year follow-up. J Cataract Refract Surg 2007;33:69-74.  Back to cited text no. 8
9.Rabinowitz YS. INTACS for keratoconus. Int Ophthalmol Clin 2010;50:63-76.  Back to cited text no. 9
10.Ertan A, Kamburoðlu G. Intacs implantation using a femtosecond laser for management of keratoconus: Comparison of 306 cases in different stages. J Cataract Refract Surg 2008;34:1521-6.  Back to cited text no. 10
11.Rodríguez LA, Villegas AE, Porras D, Benavides MA, Molina J. Treatment of six cases of advanced ectasia after LASIK with 6-mm Intacs SK. J Refract Surg 2009;25:1116-9.  Back to cited text no. 11
12.Sansanayudh W, Bahar I, Kumar NL, Shehadeh-Mashour R, Ritenour R, Singal N, et al. Intrastromal corneal ring segment SK implantation for moderate to severe keratoconus. J Cataract Refract Surg 2010;36:110-3.  Back to cited text no. 12
13.Kymionis GD, Bouzoukis DI, Portaliou DM, Pallikaris IG. New INTACS SK implantation in patients with post-laser in situ keratomileusis corneal ectasia. Cornea 2010;29:214-6.  Back to cited text no. 13
14.Kamburoglu GE, Altuner U. Comparison of response to Intacs SK and Intacs implantation in patients with advanced keratoconus. In: Free Paper Presented at the 12 th ESCRS Winter Refractive Surgery Meeting and Cornea Day, Barcelona. 2008.  Back to cited text no. 14
15.Mahmood MA, Wagoner MD. Penetrating keratoplasty in eyes with keratoconus and vernal keratoconjunctivitis. Cornea 2000;19:468-70.  Back to cited text no. 15
16.Pearson AR, Soneji B, Sarvananthan N, Sandford-Smith JH. Does ethnic origin influence the incidence or severity of keratoconus? Eye (Lond) 2000;14:625-8.  Back to cited text no. 16
17.Wagoner MD, Ba-Abbad Rola, King Khaled Eye Specialist Hospital Cornea Transplant Study Group. Penetrating keratoplasty for keratoconus with or without vernal keratoconjunctivitis. Cornea 2009;28:14-8.   Back to cited text no. 17
18.Colin J, Buestel C, Touboul D. Unusual secondary displacement of Intacs segments-superimposition of distal ends. J Refract Surg 2010;26:924-5.  Back to cited text no. 18


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]

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