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Research Letters |

Optical Coherence Tomography Provides Insight Into the Effect of Intacs in Keratoconus FREE

Igor Kaiserman, MD, MSc, MHA; Irit Bahar, MD; David S. Rootman, MD, FRCSC
Arch Ophthalmol. 2008;126(4):571-572. doi:10.1001/archopht.126.4.571.
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Published online

Keratoconus is a bilateral, asymmetric, chronic, initially progressive ectasia of the cornea characterized by steepening, distortion, and thinning of the apical cornea as well as corneal scarring.1 Intrastromal corneal ring segments (Intacs; Addition Technology Inc, Sunnyvale, California) is 1 treatment option available for patients with keratoconus, especially those with contact lens intolerance. Intacs placement in patients with mild to moderate keratoconus generally improves best spectacle-corrected visual acuity (BSCVA) and uncorrected visual acuity and reduces astigmatism.2 Intacs have generally been found to be safe and effective. However, the exact effect Intacs have on the keratoconic cornea is still debatable. Here we imaged the corneal changes induced by Intacs using comparative image analysis of optical coherence tomography (OCT).

A 54-year-old man diagnosed with keratoconus in his left eye underwent Intacs implantation after becoming intolerant to contact lenses. Preoperative BSCVA was 20/40 with a +1.50 − 4.25 × 142° correction. Anterior segment OCT (Visante OCT; Carl Zeiss Meditec, Dublin, California) was performed 1 week preoperatively using the quad line scan corneal high-resolution mode (Figure 1A). A femtosecond laser (IntraLase Corp, Irvine, California) was used to create the channels at 400-μm depth. The Intacs incision was placed on the steep axis (45°). A large segment (0.45 mm) was implanted inferiorly and a smaller one (0.25 mm) superiorly. Two weeks after surgery, BSCVA was 20/25 and the segments were well positioned. Visante OCT was performed again with the exact same parameters as preoperatively (Figure 1B). The image shows the Intacs to be partially bulging into the anterior chamber and partially compressing the stroma above them.

Place holder to copy figure label and caption
Figure 1.

High-resolution anterior segment optical coherence tomography of pre-Intacs (A) and post-Intacs (B) keratoconic cornea imaged on the 135° axis. No change was seen in the apical thickness of the cone. The thicker Intacs segment seems to compress the overlying stroma more.

Graphic Jump Location

The preoperative and postoperative images were superimposed (Figure 2A) and subtracted from one another (Figure 2B). The superimposed image shows no change in the cone's apex position after Intacs insertion. The main effect of the Intacs seems to be an elevation of the corneal stroma above the inferior segment, creating a flattening of the corneal surface in that area. Six months postoperatively, BSCVA was 20/30 with a +0.50 − 1.50 × 135° correction.

Place holder to copy figure label and caption
Figure 2.

High-resolution anterior segment optical coherence tomography images. A, The pre-Intacs (blue) and post-Intacs (red) optical coherence tomography images from Figure 1 are superimposed, showing a local elevation and flattening of the corneal surface above the thicker inferior Intacs segment (arrow). No change was noticed in the location or steepness of the cone's apex. B, The digital subtraction of the 2 images again shows the Intacs-induced elevation and surface flattening (arrow).

Graphic Jump Location

Because topographically Intacs seem to flatten and center the keratoconic cone, one would assume that they exert their effect by actually flattening and stretching the corneal apex. Based on this assumption, inserting the Intacs segments into smaller and tighter corneal channels should enhance their effect. However, Ertan et al3 found no effect of the channel size on refractive outcome. If one accepts the apex flattening assumption, one would suggest inserting 2 large (0.45 mm) ring segments to exert the largest flattening effect. Although earlier studies had advocated the use of 2 segments during the surgery,4,5 newer studies seem to find better results with just 1 inferior segment.6 Sharma and Boxer Wachler1 found significantly more improvement in uncorrected visual acuity, BSCVA, steep K values, and inferior-superior ratio and a greater cylinder decrease in the single-segment group than in the double-segment group.

Because stretching the cone can also be performed from above, some suggested inserting the thicker segment superiorly to try to center an inferiorly located cone. However, Chan and Wachler6 found that inserting the thicker segment superiorly may increase distortions and result in loss of BSCVA.

As observed using OCT, we suggest here that the effect of Intacs in keratoconus is not on the cone's apex but rather a more limited local flattening effect on the cornea surface above the segment. Because Intacs do not stretch the cone itself, it would explain why 1 inferior segment is better than 2 segments and why tighter channels should not make a difference. The local effect also explains why inserting a thicker superior segment is not as good as inserting a thicker inferior one near the steepest area of the cornea.

Correspondence: Dr Kaiserman, Department of Ophthalmology, Toronto Western Hospital, 399 Bathurst St, Toronto, ON M5T 2S8, Canada (igor@dr-kaiserman.com).

Financial Disclosure: None reported.

Funding/Support: Dr Kaiserman is a recipient of a fellowship from the American Physicians Fellowship for Medicine in Israel.

Sharma  MBoxer Wachler  BS Comparison of single-segment and double-segment Intacs for keratoconus and post-LASIK ectasia. Am J Ophthalmol 2006;141 (5) 891- 895
PubMed Link to Article
Hellstedt  TMäkelä  JUusitalo  REmre  SUusitalo  R Treating keratoconus with intacs corneal ring segments. J Refract Surg 2005;21 (3) 236- 246
PubMed
Ertan  AKamburoglu  GAkgun  U Comparison of outcomes of 2 channel sizes for intrastromal ring segment implantation with a femtosecond laser in eyes with keratoconus. J Cataract Refract Surg 2007;33 (4) 648- 653
PubMed Link to Article
Colin  JCochener  BSavary  GMalet  F Correcting keratoconus with intracorneal rings. J Cataract Refract Surg 2000;26 (8) 1117- 1122
PubMed Link to Article
Siganos  CSKymionis  GDKartakis  N  et al.  Management of keratoconus with Intacs. Am J Ophthalmol 2003;135 (1) 64- 70
PubMed Link to Article
Chan  CCWachler  BS Reduced best spectacle-corrected visual acuity from inserting a thicker Intacs above and thinner Intacs below in keratoconus. J Refract Surg 2007;23 (1) 93- 95
PubMed

Figures

Place holder to copy figure label and caption
Figure 1.

High-resolution anterior segment optical coherence tomography of pre-Intacs (A) and post-Intacs (B) keratoconic cornea imaged on the 135° axis. No change was seen in the apical thickness of the cone. The thicker Intacs segment seems to compress the overlying stroma more.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2.

High-resolution anterior segment optical coherence tomography images. A, The pre-Intacs (blue) and post-Intacs (red) optical coherence tomography images from Figure 1 are superimposed, showing a local elevation and flattening of the corneal surface above the thicker inferior Intacs segment (arrow). No change was noticed in the location or steepness of the cone's apex. B, The digital subtraction of the 2 images again shows the Intacs-induced elevation and surface flattening (arrow).

Graphic Jump Location

Tables

References

Sharma  MBoxer Wachler  BS Comparison of single-segment and double-segment Intacs for keratoconus and post-LASIK ectasia. Am J Ophthalmol 2006;141 (5) 891- 895
PubMed Link to Article
Hellstedt  TMäkelä  JUusitalo  REmre  SUusitalo  R Treating keratoconus with intacs corneal ring segments. J Refract Surg 2005;21 (3) 236- 246
PubMed
Ertan  AKamburoglu  GAkgun  U Comparison of outcomes of 2 channel sizes for intrastromal ring segment implantation with a femtosecond laser in eyes with keratoconus. J Cataract Refract Surg 2007;33 (4) 648- 653
PubMed Link to Article
Colin  JCochener  BSavary  GMalet  F Correcting keratoconus with intracorneal rings. J Cataract Refract Surg 2000;26 (8) 1117- 1122
PubMed Link to Article
Siganos  CSKymionis  GDKartakis  N  et al.  Management of keratoconus with Intacs. Am J Ophthalmol 2003;135 (1) 64- 70
PubMed Link to Article
Chan  CCWachler  BS Reduced best spectacle-corrected visual acuity from inserting a thicker Intacs above and thinner Intacs below in keratoconus. J Refract Surg 2007;23 (1) 93- 95
PubMed

Correspondence

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