Commentary: Scleral penetration or perforation during strabismus surgery

The various complications of strabismus surgery include conjunctival inclusion cyst, under- or over-correction, vortex vein damage, scleral perforation, anterior segment ischemia, orbital cellulitis and infection, and slipped or “lost” muscles.[1] Scleral perforation is one of the most severe complications. It is defined as the full thickness scleral pass of the suture needle leading to the formation of a retinal break. On the contrary, scleral penetration is defined as a full thickness scleral pass without injuring the retina.[2] Scleral penetration or perforation can occur either during suture placement in the normally thin sclera behind the muscle insertion (sclera is the thinnest behind recti insertion, 0.3 mm) or during muscle dissection, isolation, or disinsertion.[1]

The older studies reported the incidence of scleral penetration and/ or perforation was 8–12%, whereas the recent publications report a much lower incidence of 0.13–1%.[1] This decline in the complication rate has been attributed to better instrumentation and surgical techniques. However, the incidence seems to be under-estimated because of low incidence of post-operative retinal evaluation as well as serious consequences of the complication. A survey among the consultant ophthalmologists in the United Kingdom reported that 40.8% surgeons had suspected globe perforation during the surgery. However, almost 15% did not perform a post-operative dilated fundus examination.[3] Scleral penetration can lead to lens dislocation, cataract, hyphema, glaucoma, chorioretinal changes, retinal break(s), vitreous hemorrhage, retinal detachment (RD), and endophthalmitis.[1] However, unlike inadvertent perforation during peribulbar anesthesia, the incidence of sight-threatening consequences after strabismus surgery is usually low.[4] This may be because of superficial penetration limited to the choroid or formed vitreous, which tamponades the retinal breaks.[1]

Scleral perforation is usually not detected during the surgery in a majority of cases. It should be suspected in the case of sudden loss of resistance during the passage of scleral suture and appearance of choroidal pigments, vitreous, or blood. It has been reported that a needle pass through the insertional stump is not a guarantee against scleral perforation.[5] The various risk factors for scleral perforation include myopia, recession surgery, posterior fixation, the surgeon’s experience, and children (because of a small size and poor surgical access).

Placement of scleral sutures requires an accurate assessment of the needle depth and can be challenging from a top-to-down view offered by the standard microscope. Superficial sutures increase the risk of post-operative muscle slip or detachment, whereas deep sutures predispose to scleral perforation. A good surgical exposure, a dry operative field, and an adequate magnification and illumination help in appropriate suture placement. A corollary related to scleral sutures says that the needle should be visible throughout its course through the sclera to prevent perforation. However, a survey revealed that nearly 70% surgeons believed that perforation can occur even if the point of the needle is seen.[6] Microscope-integrated intra-operative optical coherence tomography (iOCT) is gaining popularity for performing corneal, glaucoma, cataract, and vitreoretinal surgeries as it provides real-time intra-operative images. It has been demonstrated to enhance the residents’ performance in depth-based anterior segment manoeuvers and may serve as a valuable tool in surgical training for residents.[7] It can be used to visualize the precise depth of the needle through both the muscle and the sclera.[8]

The treatment of inadvertent perforation during strabismus surgery is controversial. Performing culture of the affected site and instilling local and systemic broad-spectrum antibiotics have been recommended to reduce the chances of infection. The retina should be evaluated for the presence of any retinal break(s). Some authors recommend prophylactic cryotherapy to reduce the incidence of RD. However, animal experiments have found that the incidence of retinal RD was higher in eyes treated with heavy cryopexy. Prophylactic laser photo-coagulation appears to be a more promising treatment.[2,5]

We congratulate the authors for reporting three patients who developed retinal pigmentary changes 10 years after strabismus surgery, suggestive of iatrogenic scleral perforation during the surgery.[9] Villegas et al. had earlier reported three patients with chorioretinal scar and/or retinal pigment epithelial (RPE) changes in the periphery. The location of these changes coincided with the site of strabismus surgery.[10] Park et al. reported the presence of chorioretinal scar, focal atrophic change, and spot and fibrotic reaction in eight eyes of six patients who have undergone a previous strabismus surgery. Because these findings were around the suture area, they were also presumed to be secondary to the previous scleral perforation.[11] However, it remains inconclusive if these changes can occur secondary to intra-operative penetration, other surgical manipulations such as grasping the sclera with forceps, post-operative suture migration, or inflammation.

Long-term prospective studies should be planned to detect serial retinal changes after strabismus surgery. Such studies can help estimate the incidence of scleral perforation and the timing and cause of these chorioretinal changes. Routine examination with indirect ophthalmoscopy is recommended during follow-up of these patients. Young children may not be cooperative for such an examination. The ultra-wide-field retinal imaging platforms can help screen the peripheral retina in such patients.[12]