From Iris Advanced Eye Centre, CMC Hospital, Chandigarh, India (Bedi); and the Department of Ophthalmology, Pellegrin Hospital, Bordeaux, France (Touboul, Pinsard, Colin).
Dr Colin is a consultant for Addition Technology Inc (Des Plaines, Illinois). The remaining authors have no proprietary interest in the materials presented herein.
Study concept and design (J.C.); data collection (L.P., J.C.); analysis and interpretation of data (R.B., D.T.); drafting of the manuscript (R.B.); critical revision of the manuscript (R.B., D.T., L.P., J.C.); statistical expertise (R.B.); administrative, technical, or material support (D.T., L.P.); supervision (J.C.)
Correspondence: Joseph Colin, MD, Service d’Ophtalmologie, CHU Pellegrin, Place Amelie Raba-Leon, 33706 Bordeaux Cedex, France. E-mail: email@example.com
Keratoconus is a progressive, noninflammatory, bilateral corneal ectasia that is characterized by paraxial stromal thinning and paracentral cone-shaped steepening of the cornea, which result in irregular astigmatism and refractive myopia.1 The goals of keratoconus management are three-fold: 1) to correct the corneal ectasia and restore the normal prolate shape of the cornea; 2) to improve the associated refractive error and aberrations; and 3) to arrest the progression of keratoconus.
Various technologies have been advocated for the management of keratoconus, including keratorefractive options (radial keratotomy,2 astigmatic keratotomy,3 photorefractive keratectomy,4 and LASIK5), intracorneal ring segments,6 corneal collagen cross-linking (CXL),7 and toric phakic intraocular lenses (PIOLs).8 Among these, intracorneal ring segments and CXL address, at least partly, all three aims of keratoconus treatment.9–11 In contrast, keratorefractive treatments have been reported to weaken the structural integrity of the cornea12–14 and toric PIOLs do not address corneal shape and progression.
In the past decade, Intacs (Addition Technology Inc, Des Plaines, Illinois) implantation has been extensively documented to correct ectasia and associated refractive error and aberrations in eyes with keratoconus as well as maintain long-term refractive results for almost 10 years with no need for keratoplasty.15 However, no previous publication has investigated the progression of keratoconus in eyes implanted with Intacs using the methods recently documented for corneal collagen CXL. Therefore, this study was designed to evaluate the long-term risk of keratoconus progression in eyes implanted with Intacs.
Patients and Methods
In this retrospective case review, the data of 105 eyes from 85 patients who had undergone consecutive Intacs (standard) implantation at the Department of Ophthalmology, Pellegrin Hospital, Bordeaux, France between January 2001 and December 2005, were analyzed for the presence of progression between 1 and 5 years postoperatively. Intacs segments were implanted at approximately 70% depth of the corneal thickness at the site of the incision using the same technique and nomogram as documented in the European clinical evaluation study.16 The study adhered to the tenets of the Declaration of Helsinki and institutional review board approval was obtained.
Upon literature review, it was determined that no consistent definition of progression of keratoconus has been reported in previous publications. Among the multiple criteria that have been used to define progression—need for a new contact lens fit ⩾1 time in 2 years,17 decreased visual acuity reported by the patient,18 increase in steep keratometry (K) of ⩾1.00 diopter (D) over 12 months,17 decrease in sphere by ⩾0.50 D, and decrease in cylinder by ⩾1.00 D19—increase in steep K is the most direct measurement of progression compared to the other parameters such as the change in visual acuity or need for contact lens refitting. For that reason, increase in steep K has been included as one of the criterion for progression in all previous publications.
Therefore, we decided to use a definition of progression based on change in steep K. For the diagnosis of preoperative progression, we used the definition of progression, similar to the earlier literature, ie, an increase in steep K of ⩾1.00 D over a 12-month period.17 To evaluate postoperative progression, we used an even more rigorous definition—increase in steep K of ⩾1.00 D over 4 years between 1- and 5-year follow-up.
Based on the preoperative data, all eyes were categorized into three groups: eyes with documented preoperative progression (change in steep K ⩾1.00 D over 12 months), eyes with documented absence of preoperative progression (change in steep K <1.00 D over 12 months), and eyes with no record of presence or absence of preoperative progression (and underwent Intacs implantation for refractive reasons). In addition to evaluating all eyes together for the presence of postoperative progression between 1 and 5 years postoperative, progression was also evaluated for eyes in the individual subgroups. Additional study parameters included steep K, flat K, average K, manifest refraction spherical equivalent (MRSE), uncorrected distance visual acuity (UDVA), and corrected distance visual acuity (CDVA) at 1- and 5-year follow-up.
Statistical analysis was performed using SPSS software (SPSS Inc, Chicago, Illinois). A paired t test was used to compare the mean outcomes of steep K, flat K, average K, MRSE, UDVA, and CDVA at 1 and 5 years postoperatively. All statistical analyses were carried out using a two-sided α of 0.05.
Mean age of the 85 patients was 30.1±7.5 years (range: 16 to 52 years). Amsler-Krumeich grading and cone type (central, global, and asymmetrical distribution), as used in the European clinical evaluation study,16 of the 105 eyes are summarized in Table 1. The 105 eyes were divided into three categories based on the presence/absence/non-documentation of preoperative progression (Table 2). At 1-year follow-up, data from 92 eyes were available for analysis, as 1 eye had presented with extrusion and 12 had undergone removal of Intacs because of unsatisfactory results either due to steep K >55.00 D or central corneal thickness <350 μm, or both. These eyes were managed by penetrating or deep lamellar keratoplasty. At 5-year follow-up, data of all 92 eyes were available for analysis.
Table 1: Keratoconus Severity Grading and Cone Type Classification of Eyes That Underwent Intacs Implantation
Table 2: Cessation of Progression Outcomes Following Intacs Implantation in Eyes With Keratoconus
Overall, 8 (8.7%) of 92 eyes demonstrated >1.00-D progression of steep K over 4 years between 1- and 5-year follow-up. In the subgroup analysis, of the 56 eyes with documented preoperative progression, 4 (7.1%) eyes demonstrated progression between 1 and 5 years postoperatively; of the 24 eyes with documented absence of preoperative progression, only 1 (4.2%) eye demonstrated progression; and of the 12 eyes with no record of preoperative progression, 3 (25%) eyes demonstrated progression (Table 2). Additional analysis was performed in which all eyes with no record of preoperative progression were imputed as having preoperative progression; of the 68 eyes having documented/imputed progression, 7 (10.3%) eyes demonstrated progression between 1 and 5 years.
No statistically significant differences (P>.05) were found for mean visual, refractive, and keratometric parameters (steep K, flat K, average K, MRSE, UDVA, and CDVA) of the 92 eyes between 1 and 5 years postoperative (Fig).
Figure. Comparison of mean keratometric, refractive, and visual outcomes between 1- and 5-year postoperative follow-up demonstrating the stability of Intacs outcomes. K = keratometry, MRSE = manifest refraction spherical equivalent, UDVA = uncorrected distance visual acuity, CDVA = corrected distance visual acuity
The objectives of keratoconus management have evolved over time; aside from managing refractive/aberrometric error and deferring keratoplasty, halting progression of keratoconus is now one of the key aims of keratoconus management. Many publications have documented the long-term results of the stability of the refractive outcomes of Intacs implantation in eyes with keratoconus.9,15,20,21 Additionally, analysis of the previous publications on keratoplasty after Intacs (whether penetrating or lamellar) revealed that keratoplasty was performed for suboptimal visual improvement after Intacs implantation and not because keratoconus had progressed.22–24 Although these previous publications indicate that Intacs implantation may impede keratoconus progression, no study to date specifically evaluates the long-term data for halting progression of keratoconus.
We analyzed the 1- and 5-year data of 105 eyes implanted with Intacs to determine the rate of progression. We used a more stringent definition of progression, ie, increase in steep keratometry of ⩾1.00 D over 4 years compared to 1 year in previous publications. We found that 91.3% of eyes had no progression over the 4-year period. Analysis of the data of the subgroup of eyes with documented preoperative progression revealed that 92.9% of eyes did not show any progression between 1 and 5 years postoperatively.
Results are comparable to studies of CXL, which have reported that 86% to 92.4% of eyes remained stable or improved when comparing progression from pre- to 12-month postoperative CXL.17,25,26 We reemphasize that our study compares the progression of steep K at 1 and 5 years after Intacs implantation compared to before versus 12 months after CXL. However, a similarly designed study comparing preoperative Intacs and 5-year postoperative Intacs data would not have been able to differentiate between the refractive outcomes and progression outcomes. Because the refractive outcomes of Intacs are known to continue to improve until 6 months after implantation,27 we decided to study any progression after 1 year of implantation. Therefore, our study design allows us to infer that 92.9% of eyes with progressive keratoconus did not progress after the refractive outcomes stabilized.
Absence of progression in 92.9% of eyes with keratoconus from an apparently mechanical procedure intrigued us to research the literature in detail to find any possible reasons for such an observation. Potential explanations may lie in keratocyte activation (with a consequent increase in keratocyte density) and new collagen formation,28,29 which are known to manifest after Intacs implantation. However, appropriately designed experiments are necessary to determine a precise reason. An alternative explanation, at least in some of the patients, may be the natural cross-linking with increasing age.30,31 Future studies may be directed at evaluating progression in younger patients with progressive keratoconus.
In the subgroup with nonprogressive keratoconus preoperatively, the presence of postoperative progression in 1 (4.2%) eye signifies a small but potential long-term risk of recommencement of progression and therefore the need for continued long-term monitoring of eyes with keratoconus, whether or not currently progressive.
The combined procedure of Intacs implantation with CXL has been reported to be additive for refractive outcomes.9,32–34 Although validation in future studies is needed, the results of our study suggest that the combined procedure of Intacs and CXL may also augment stability outcomes of the individual procedures.
The 5-year data of our study demonstrate the long-term stability of refractive and topographic outcomes in eyes implanted with Intacs. The finding that 92.9% of eyes with progressive keratoconus did not progress postoperatively indicates that Intacs implantation may be a potential therapeutic option to halt progressive keratoconus.
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- Utine CA, Bayraktar S, Kaya V, et al. Radial keratotomy for the optical rehabilitation of mild to moderate keratoconus: more than 5 years’ experience. Eur J Ophthalmol. 2006;16(3):376–384.
- Krumeich JH, Kezirian GM. Circular keratotomy to reduce astigmatism and improve vision in stage I and II keratoconus. J Refract Surg. 2009;25(4):357–365. doi:10.3928/1081597X-20090401-07 [CrossRef]
- Cennamo G, Intravaja A, Boccuzzi D, Marotta G. Treatment of keratoconus by topography-guided customized photorefractive keratectomy: two-year follow-up study. J Refract Surg. 2008;24(2):145–149.
- Appiotti A, Gualdi M. Treatment of keratoconus with laser in situ keratomileusis, photorefractive keratectomy, and radial keratotomy. J Refract Surg. 1999;15(2 Suppl):S240–S242.
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- Wollensak G. Crosslinking treatment of progressive keratoconus: new hope. Curr Opin Ophthalmol. 2006;17(4):356–360. doi:10.1097/01.icu.0000233954.86723.25 [CrossRef]
- Kamiya K, Shimizu K, Ando W, Asato Y, Fujisawa T. Phakic toric Implantable Collamer Lens implantation for the correction of high myopic astigmatism in eyes with keratoconus. J Refract Surg. 2008;24(8):840–842.
- Piñero DP, Alió JL. Intracorneal ring segments in ectatic corneal disease—a review. Clin Experiment Ophthalmol. 2010;38(2):154–167. doi:10.1111/j.1442-9071.2010.02197.x [CrossRef]
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- Kolli S, Aslanides IM. Safety and efficacy of collagen crosslinking for the treatment of keratoconus. Expert Opin Drug Saf. 2010;9(6):949–957. doi:10.1517/14740338.2010.495117 [CrossRef]
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Keratoconus Severity Grading and Cone Type Classification of Eyes That Underwent Intacs Implantation
|Keratoconus Grade*||Cone Type||Total|
Cessation of Progression Outcomes Following Intacs Implantation in Eyes With Keratoconus
|Subgroup*||No. of Eyes (%)|
|Implanted With Intacs||Intacs Removed||Extrusion of Intacs||Evaluated at 1 & 5 Years||No Progression From 1 to 5 Years||Progression ⩾1.00 D Between 1 and 5 Years|
|Progressive||62||5||1||56||52 (92.9)||4 (7.1)|
|Nonprogressive||27||3||0||24||23 (95.8)||1 (4.2)|
|Progression data not available||16||4||0||12||9 (75.0)||3 (25.0)|
|Total||105||12||1||92||84 (91.3)||8 (8.7)|