of autologe blood may also be considered. Refractive changes: Postoperative refractive changes may also occur with MISS openings, especially with larger displacements. Their frequency and size seem to be comparable to changes seen using HarmsÕ limbal opening [9]. Permanent increase of conjunctival redness: Hardly ever will the MISS technique permanently increase the conjunctival redness visible in primary position. In contrast, after rectus muscle surgery, seldom will a permanent increase of redness be seen on eccentric gaze. Often in these patients the opposite, unoperated eye, will disclose larger vessels and a slight redness of the conjunctiva in the region of the muscle insertion. If this is seen preoperatively, the patient should be informed that possibly this redness will increase. In severe cases having a normal perilimbal conjunctiva, it might be advisable to avoid MISS openings and do surgery using HarmsÕ limbal approach with two short relaxing cuts. Permanent, increased, perilimbal redness may be seen in a few patients after converting the small openings to a large HarmsÕ limbal opening. Therefore, the surgeon should Þrst try if the operation can be continued by a enlarging the two small cuts before joining them at the limbus. Repeat surgery after MISS: If a muscle, which has been operated through MISS openings, needs repeat surgery, the same conjunctival access should be used. Usually, the previous scar will be visible, at least if the microscope is used to perform the procedure. Often, because of increased parainsertional scarring, the cuts need to be slightly larger.

6.8Suggestions on How to Start Doing MISS

6.8.1 Instruments Suitable for MISS

Instruments indispensable for strabismus surgery are as follows: eye speculum, forceps, scissors, muscle hooks, spatula calipers, needle-holders, clips, sponge-swabs and cautery. While usually for open surgery the size of the instruments is not critical, conjunctival tearing will occur if very large instruments are used to operate through MISS keyhole openings. Table 6.1 includes a list of instruments suitable to perform MISS. It is up to every surgeon to decide if he wants to switch to the suggested instruments or if he believes that MISS may also be performed with the instruments he has. Using his own instruments, as long as they work, will probably make transition easier. The following instruments are useful to perform MISS. By clamping a serreÞne to the eyelid speculum, a hypomochlion is created for traction sutures applied medially (Fig. 6.17a, b). A colibrie forceps with interdigitating teeth is used to Þx the conjunctiva while performing the keyhole openings and to stabilize the eye for traction and scleral anchoring sutures (Fig. 6.17c). A small, curved needle holder is optimal to perform suturing through small openings (Fig. 6.17d). A small conjunctival scissor with a curved, blunt tip is used to cut the conjunctiva, the sutures and the muscle or tendon insertions (Fig. 6.17e). Curved forceps with serrated tips should be used to hold the conjunctiva after performing the keyhole openings as this

Fig. 6.17 Useful instruments to perform MISS. (a, b) Eyelid speculum with serreÞne, (c) colibrie forceps, (d) needle holder, (e) curved scissors, (f) curved forceps, (g) small, medium and

large spatula, (h) bipolar, coaxial diathermy, (i) small strabismus hook, (j) angled forceps, (k) calipter, (l) blunt cannula

will prevent unnecessary conjunctival trauma (Fig. 6.17f). Spatulas of different sizes are useful to visualize the tissue through the small, conjunctival cuts (Fig. 6.17g). Diathermy is best performed using a system with a bipolar, coaxial tip (Fig. 6.17h). This will allow gentle cauterization of vessels at the muscle insertion through the tunnel, without damaging the overlying conjunctiva. A small strabismus hook can be easily introduced through the small openings (Fig. 6.17i). Angled forceps are necessary to stabilize the muscle insertion during desinsertion (Fig. 6.17j). By pressing the tips of Castroviejo calipers for about ten seconds against the sclera, a bluish indentation mark is formed, which will be visible for up to one minute (Fig. 6.17k). This indentation technique works also transconjunctivally, as there

is no need to apply a dye to the tip. A blunt cannula is helpful to safely displace a needle through a tunnel (Fig. 6.17l). This is necessary for MISS inferior and superior oblique recessions and MISS rectus muscle transpositions.

6.8.2 Suture Materials Used for MISS

The limbal traction suture is performed with PERMAHand silk¨ 6Ð0 (Ethicon), with a round needle (BV- 1). Having no cutting edge, such needles will minimize the risk of scleral tearing. The inconvenience of round needles is the difÞculty in guiding them because they

cannot be held Þrmly by the needle holder. For scleromuscular attachment in recessions and plications of rectus muscles and the inferior oblique muscle, Vicryl¨ 7Ð0 with a GS-9 spatula needle (Ethicon) is used. This synthetic, braided suture will be fully absorbed after 3 months. The spear-shaped needle can be grasped Þrmly and minimizes the risk of scleral penetration. Some surgeons believe that diamond-shaped spatula needles further reduce the risk of injury to the retina. For scleromuscular attachment in recessions and plications of the superior oblique muscle and for retroequatorial myopexia, a nonabsorbable PremiCron¨ 5Ð0 with 3/8 taper point needle (B.Braun) is used. Vicryl¨ 8Ð0 rapid, a synthetic, braided suture with a GS-9 spearshaped spatula needle (Ethicon) is used to readapt the TenonÕs capsule and the conjunctiva.

6.8.3General Remarks Regarding MISS Procedures

Although it might not be mandatory to use the operating microscope to perform minimally invasive strabismus surgery, its use will certainly help to further reduce tissue traumatism and to control intraoperative bleeding better. The higher magniÞcation will also help to perform scleromuscular sutures more precisely and, may, therefore, decrease the risk of globe penetration. Theoretically, a certain freedom of movement can be retained by rotating the operating microscope and the surgeonÕs chair, depending on which eye is being operated, which surgical procedure is done, or within the same procedure, depending on which surgical steps are done. However, as usually the immobility of the surgeonÕs body can be easily compensated by an increase in arm movements and by learning to perform more demanding tasks like suturing with the non dominant hand, it is advisable to always sit at the head of the operating table. Surgeons switching from magnifying glasses to the operating microscope should Þrst get used to the unusual situation by performing several procedures with their own technique. First, easy operations such as primary muscle recessions, resections and plications should be performed. Then, more demanding procedures such as repeat surgeries, posterior muscle anchorages and transposition can be carried out. Only then, a transition to minimally invasive techniques is advisable. Again, when starting with MISS, several primary

recessions and plications should be performed before going for more difÞcult operations. Although muscle resections also could be performed using two keyhole openings, transition to plications is recommended. Surgeons inexperienced with plications would beneÞt from trying it Þrst with open surgery, using HarmsÕ limbal approach. Initially, it is inevitable that instrument introduction, use, and retraction through the keyhole openings will be associated with larger displacements of the openings. With more experience, the surgeon will learn to minimize such displacements as they induceconjunctival tearinginolderpatients.Fortunately, usually, a tear will remain without any consequence as long as the TenonÕs tissue is not involved and it is not over the muscle. In order to minimize the risk of conjunctival tearing, avoid initially patients older than approximately 40 years and also patients younger than approximately 14 years, because with increasing thickness of the TenonÕs capsule, keyhole surgery becomes more demanding. It is recommended that children below the age of 2 years are only operated with MISS by experienced surgeons. The keyhole opening sizes mentioned in previous chapters will usually be too small for beginners. Therefore, do not hesitate to initially increase the cut size. Postoperative swelling, redness, and patient discomfort will be less compared to most other access techniques. Rectus muscle recessions and plications of more than 4 mm are also more demanding, compared to muscle displacements of 4 mm or less. Muscular Þbrosis, e.g., secondary to thyroid endocrine orbitopathy, will also make surgery more difÞcult, because of decreased passive eye rotations; therefore, a more posterior location of the cuts is recommended. In summary, it is recommended that surgeons start with MISS in patients aged between 14 and 40 years, needing primary rectus muscle recessions or plications of 4 mm or less. The level of difÞculty will not differ, whether only a rectus muscle displacement is performed in an eye or combined with a displacement of another muscle.

6.8.4 MISS Dose–Response Relationships

MISS muscle displacements are performed in the same manner as open surgery. Therefore, it seems rather unlikely that doseÐresponse will differ if the operating technique is changed. However, it is mandatory that muscle sutures,