Intrastromal corneal ring segments (ICRSs) such as Intacs (Addition Technology, Inc., Sunnyvale, California) can be used to treat mild to moderate myopia and keratoconus. They are inserted intrastromally into a track that is created using either a mechanical dissector or a femtosecond laser such as the IntraLase (Abbott Medical Optics Inc., Santa Ana, California). Most ICRSs are inserted without incident; however, they can occasionally enter a false plane, creating a risk of suboptimal positioning and possible collapse of the actual track. This article presents a simple technique for removing the Intacs segment from the false plane so that it may be reinserted into the correct channel. A video of the technique may be viewed at www.eyetube.net/video/turnaround- technique-for-intacs-false-channel-creation/.
CREATING THE CHANNEL
The size and depth of channels created by femtosecond laser are precise, and the incidence of shallow placement or perforation into the anterior chamber or superficially is low. The surgeon can program the femtosecond laser to create a 360° circumferential channel at the desired depth and a vertical entry incision at the desired axis (Figure 1). The Intacs segments are inserted perpendicular to the corneal surface to the depth of the incision (Figure 2A), then turned horizontally, parallel to the channel, and introduced into the channel. Once the segment is within the channel, it is further advanced with short pushes in the plane of the tunnel, maintaining the arc of the tunnel (Figure 2B). Once it is in position, the procedure is repeated on the other side with the second segment.
Typically both segments slide smoothly into their tunnels. However, a segment occasionally becomes snagged along the arc of insertion. This happens if, instead of following the femtosecond channel, the segment creates a false plane. This false channel will enlarge with further pushing, causing possible collapse and loss of the femtosecond channel plane. Further pushing at this stage is pointless, as it leads only to the creation of a blind track.
False channel creation is associated with difficult insertion, sometimes resulting in abandonment of the procedure (Figure 3A) or suboptimal positioning of the segments (Figure 3B). In our experience, excessive maneuvering and repeated attempts at insertion, even in the face of obstruction, can lead to complications.
The turnaround technique, conceived by one of us (SJ), is ideal for handling Intacs segments, either symmetric or asymmetric, that enter a false channel. Below is a description of how this technique is used to correct the loss of the channel plane. As soon as the surgeon experiences difficultly during insertion (Figure 4), the ICRS should be removed, turned around, inserted into the opposite end of the channel (Figure 5), and advanced as far as possible with forceps. The second Intacs segment is then inserted and is used to push the first segment into the correct position (Figure 6); the arc shape of the ICRS makes it the perfect instrument for this purpose. This maneuver allows the leading edge of the first segment to glide into the right plane by opening the IntraLase-dissected channel (Figure 7).
The continuous circular 360° channel allows circumferential movement of the segment. The first segment is pushed forward through the IntraLase channel into the area of false dissection until it has reached the intended site of implantation. The second segment is then manipulated back to its intended site using a reverse Sinskey hook to engage its positioning hole (Figure 8).
RECOGNIZING FALSE CHANNEL DISSECTION
When the advancing edge of the Intacs segment enters into a plane other than the one created by the femtosecond laser, further advancement leads to cleavage of a new plane. Formation of this false channel is clinically recognizable by progressive difficulty of insertion and forward movement of the segment. Resistance to the advancing edge of the segment is visible in the corneal stroma, appearing as a wavelike deformity and radiating folds at the advancing edge of the segment (Figure 4).
Forcing the segment forward enlarges the false channel. Because it is adjacent to the IntraLase-dissected channel, compaction of the adjacent lamellae occurs, with resultant collapse of the IntraLase channel. At its point of origin, the false channel is separated from the IntraLase channel by an internal lip in the corneal stroma (Figure 9A), which opens toward the entry incision. On careful examination, the internal lip can be identified clinically. The Intacs segment or any instrument introduced through the entry incision is guided away from the IntraLase channel and into the false channel by this internal lip. The turnaround technique is so named because the ICRS is turned around and introduced from the opposite side when a false channel is detected. Approaching the obstruction from the opposite side flattens the internal lip, making the false channel collapse and reopening the IntraLase-dissected channel (Figure 9B). The segment should be guided from the opposite direction into the IntraLase-dissected plane. The segment can be seen crossing the internal lip when it is turned around and introduced from the opposite side.
SYMMETRIC AND ASYMMETRIC SEGMENTS
Symmetric segments. If the second of two ICRSs causes false channel dissection, remove that segment and use it to push the first one forward. This segment will now be lying in the area of obstruction. If it is the first segment that has entered the false channel, it should be removed and inserted from the opposite direction. The second segment is then used as a pushing tool so that the first segment approaches its intended site from the opposite direction.
Asymmetric segments. If the second ICRS does not pass with ease, remove it and perform a double-pass turnaround technique. After the obstructed second ICRS is removed and used to push the first ICRS forward, the position of the ICRSs is the reverse of what is desired. The first ICRS is manipulated out through the incision site. This externalized ICRS is then reintroduced into the channel and used to push the second ICRS forward until both ICRSs come to rest in their respective planned sites.
False channels, if not tackled appropriately, may result in abandoned implantation of one or both ICRSs. In some instances, suboptimal positioning with regard to plane or axis may occur; however, the turnaround and the doublepass turnaround techniques are useful strategies to correct these errors and to overcome this difficult situation.
Amar Agarwal, MS, FRCS, FRCOphth, is Director of Dr. Agarwal Eye Hospital and Eye Research Centre, Chennai, India. He states that he is a consultant to Abbott Medical Optics Inc. Professor Agarwal may be reached at tel: +91 44 2811 6233; e-mail: firstname.lastname@example.org.
Soosan Jacob, MS, FRCS, DNB, MNAMS, is a Senior Consultant Ophthalmologist at Dr. Agarwal Eye Hospital and Eye Research Centre, Chennai, India. She states that she has no financial interest in the products or companies mentioned. Dr. Jacob may be reached at tel: +91 44 2811 6233; e-mail: email@example.com.
• If an ICRS becomes snagged along the arc of insertion, do not push the segment any further.
• Instead, remove the ICRS, turn it around, and insert it into the opposite end of the channel, advancing as far as possible.
• The second ICRS moves the first into the correct position.