Evaluation of intended versus actual Intacs intracorneal ring segment depth using OCT

Session Details

Session Title: Cornea Surgical II

Session Date/Time: Tuesday 16/09/2014 | 08:00-10:30

Paper Time: 09:21

Venue: Boulevard B

First Author: : R.Borbara UK

Co Author(s): :    A. Barbara   M. Naftali           

Abstract Details

Purpose:

To compare the actual versus intended depth of intacs intracorneal ring segments implanted in eyes with keratoconus using OCT. To examine whether segment thickness influence its depth of implantation, and whether two segments implanted in the same eye would tend to be at similar depths as they both share the same incision. Moreover, we aimed at looking whether stromal compression occurs after segment implantation.

Setting:

Ophthalmology Department, Hadassah Optimal Medical Center, Haifa, Israel

Methods:

This is a prospective study approved by the Helsinki board for 30 Intacs segment depth measurement. The surgical procedure was performed by the same surgeon (AB) according to the company's manual and instructional course. Segment implantation was performed under topical anesthesia using the manual technique aiming at 80% corneal depth as measured intraoperatively by a pachymeter done at the incision site and of the hypothetical channels as marked by the special Intacs marker. Dissection was performed using a channel guide in clockwise and counterclockwise directions. Data collected were; segment size, expected depth of segment and the actual postoperative ICRS depth as measured by OCT (OPKO Spectral OCT/SLO™) at 3 points for each segment; proximal, central and distal to the incision site. Depth measurement was performed above and below the segment for each of the 3 points. The data collected into a chart and SAS software was used for all the statistical analyses which included ANOVA (Analysis of Variance), matched t-test, a mixed model and the GLIMMIX procedure.

Results:

Thirty Intacs intracorneal rings segments implanted in Nineteen eyes of 15 patients with keratoconus. On average the segment tended to be 153 ?m more superficial than was intended. The proximal part of the segment tended to be superficial in relation to the rest of the segment by 13 ?m with statistical significance, the distal part of the segment tended to be deeper by 12 ?m with statistical significance. The central part was slightly deeper than average by 1 ?m but that was not statistically significant. Segment thickness was not found to influence segment depth of implantation. Moreover, two segments implanted in the same eye did not seem to be at similar depth compare to the rest of the segments in the study. Our results also show that we cannot reject the hypothesis that anterior and/or posterior compression of the corneal lamella is not present following segment implantations. Small sample size was a limiting factor in proving this hypothesis.

Conclusions:

ICRS are aimed to be implanted at 80% corneal depth in the area of implantation. Different instruments have been previously applied using to measure its depth of implantation using slit lamp, Pentacam and anterior-segment OCT with variable accuracy. Different measurement methods using OCT have been proposed; measuring corneal thickness only above the segment or measurement till the inner radius of the segment. To our knowledge our group is the 1st to report on segment depth measurement using anterior segment OCT by quantifying corneal thickness above and below the segment which we believe is a more accurate method for assessing true segment depth. Although neighboring Intacs segments share the same incision site and depth of incision, they did not tend to be at similar depths when compared to all segments in the study. This point indicates that the crucial part in determining segment depth is the pocketing stage and not the depth of incision performed by diamond knife which is set at 80% of corneal thickness at the incision site. Segment thickness did not influence depth of implantation. Intacs segments are implanted more superficial than intended by 153 ?m. The proximal part of the segment tended to be more superficial in relation to the rest of the segment and the distal part deeper. In other words, as we create the pocket with the dissector, the proximal part of the pockets is shallow and as we keep on dissecting we move deeper into the cornea. Anterior and/or posterior lamellar compression cannot be rejected in this study. A larger sample size is needed to prove this point.

Financial Interest:

NONE