Perforation of the choroid and retina during strabismus surgery is fairly common. Gottlieb and Castro1 noted funduscopic lesions indicating perforation of the globe with a needle in 9.2% of a group of children who had undergone corrective surgery for strabismus previously. Since approximately 83,000 strabismus operations are performed annually in the United States2 one can extrapolate an incidence of 7,600 scierai perforations during strabismus surgery per year. It has been suggested on theoretical grounds that should this common complication occur, cryopexy of the surrounding retina is indicated.3 The purpose of this report is to investigate the natural history of scierai perforation in rabbits and the effect of cryocoagulation to the surrounding tissue in altering its natura) course.
Materials and Methods.
Pigmented and non-pigmented rabbits weighing approximately 2.5 kg were anesthetized using xyiazine 10 mg per kg and ketamine 20 mg per kg. A conjunctival peritomy was performed exposing bare sclera for approximately 12 mm posterior to the limbus. A 5-0 polyglactin suture on a spatula needle was passed through the sclera and into the vitreous twice at this point invariably resulting in vitreous loss and hemorrhage within the eye. The suture was then tied and left in place (Figure 1). In ten eyes the procedure was then terminated. In an additional twenty eyes transscleral cryopexy was applied utilizing a carbon dioxide probe which froze at approximately -60°C. In ten of these eyes, a single application was applied directly over the scierai perforation site achieving approximately 20 seconds of cryocoagulation of the retina. This we felt simulated proper clinical treatment. In an additional ten eyes, seven additional applications were applied to the lesion, simulating an excessively intense heavy treatment. Finally, an additional four eyes had this similar heavy cryocoagutation alone, without a scierai perforation having been previously made. The rabbits were then examined three weeks later and a determination was made as to the status of the retina. The rabbits were then sacrificed using intracardiac pentobarbital.
FIGURE 1: Tino 5-0 dyed polyglactin sutures which are tied externally are seen ophthalmoscopically within the vitreous.
In those eyes in which a scierai perforation was made and no cryo was applied, the retinas of nine eyes remained attached (Figure 2) while one retinal detachment developed (Tablel, In those eyes treated with a single cryo application nine eyes also remained attached while one retina detached. In the group of four eyes treated with cryocoagulation alone and no scierai perforation, no detachments were noted. However, in the ten eyes treated by scierai perforation and very heavy cryocoagulation, eight retinal detachments were diagnosed (Figure 3), while only two retinas remained attached. Thus, heavy cryocoagulation appeared to increase the propensity for retinal detachment following scierai perforation (p < .01).
McLean, Galin, and Baras* described the course of retinal perforation during strabismus surgery in 1960. They noted a rather consistent sequence of events which occurred following the induction of needle track retinal tears in young healthy eyes. Initially, hemorrhage covered the perforation site. Occasionally, some of this hemorrhage was noted to break through into the vitreous cavity, but generally it remained confined to the choroid and retina. In a matter of a day or two the sclera was visible, usually surrounded by residual hemorrhage and light pigmentation. The area appeared as if the retina and choroid were scooped out leaving bare sclera behind.
They then performed a detailed ophthalmoscopic examination of a group of strabismus patients in the immediate postoperative period, and in a "rather short period of time" found 16 patients in whom this complication occurred. Photocoagulation was used to treat the first two of these patients. The remaining 14 were left untreated and in no case did detachment occur. They inferred, therefore, that no therapy was indicated. Gottlieb and Castro,1 however, in 1970, reported several complications resulting from perforation of the globe during strabismus surgery. They described two retinal detachments occurring four months and three years respectively postoperatively, a severe vitreous hemorrhage and one case of endophthalmitis both of which developed within one month after surgery. They then prospectively also examined an additional 65 patients immediately after strabismus surgery and found six funduscopic lesions indicating perforation of the globe with a needle among these patients. None of these patients developed any other complications. Of interest, they noted that in all ten patients in whom perforation of the globe occurred during strabismus surgery, the surgeon did not notice this complication occurring intraoperatively.
FIGURE 2: Appearance of the retina three weeks after perforation with no fryopexy. Retina is firmly attached.
FIGURE 3: Appearance of the retina three weeks after perforation and excessive cryopexy. "fractional retinal detachment !arrow) is noted.
Basmadjian, Labelle, and Dumas15 examined three patients over a six-year period in whom retinal detachment occurred five to eight years after strabismus surgery. They noted features common in these patients which included the presence of a chorioretinal scar corresponding in location to the muscle operated upon, proliferating fibrous tissue adjacent to the scar and varying degrees of vitreous hemorrhage. They advised the use of diathermy or cryo application over the perforation site in case such an accident should be suspected.
Salamon, Friberg, and Luxenberg*1 described a patient in whom a scierai perforation occurred during strabismus surgery and was immediately treated by cryopexy. The patient, unfortunately, developed endophthalmitis and despite intensive antibiotic and cor t i costero id therapy retained only light perception vision in that eye. They also described another patient with a blind painful eye apparently secondary to endophthalmitis following extraocular muscle surgery presumably associated with scierai perforation, although none was ever definitely seen. Other cases of endophthalmitis following scierai perforation during strabismus surgery have been reported by Havener and Kimball,7 and by McNeer.8 Other complications reported include cataract,7 hyphema,7 and lens dislocation.9
Although every rhegmatogenous retinal detachment begins with a retinal break, most retinal breaks do not lead to a retinal detachment. It is generally felt that the most important factor is degeneration or detachment of the overlying vitreous and traction exerted by the vitreous on the retinal tissue producing a retina) tear which allows fluid vitreous to get behind the retina and separate it from its layer of pigment epithelium.10 Machemer11 was unable to produce a retinal detachment in owl monkeys by simply perforating the sclera, choroid, and retina with a 26-gauge needle. Only after he repeated the experiment concurrently injecting hyaluronidase into the vitreous cavity to produce h'quification of the gel, did detachment of the retina occur. Cleary and Ryan12 also studied the natural history of experimental posterior penetrating eye injury in the rhesus monkey. They produced an 8-mm long wound into the vitreous through the area of the pars plana. In six eyes, the vitreous was replaced with balanced salt solution prior to closure and retinal detachment did not occur. In 40 eyes, however, 0.5 ml of autologous blood was injected into the midvitreous instead of balanced salt solution. In half of these eyes, traction retinal detachment developed, characterized by intraocular fibrosis and the formation of cyclitic, epiretinal and subretinal membranes. Thus, in monkeys, retinal detachments do not occur following a simple sclera! and retinal perforation unless the quality of the vitreous is altered.
When a retina) tear is associated with vitreous traction and/or degeneration, transconjunctival or transscleral retinal cryopexy may be used to produce a chorioretinal adhesion and prevent a retinal detachment. Hi sto logically, one sees proliferation and metaplasia of pigment epithelial cells, Mueller cell hypertrophy and proliferation of astrocytes,13 which leads to an adhesion between the retinal pigment epithelial layer and the neurosensory retina by both desmasomal attachments and villus interdigitation,14
Kirkconnel and Rubin15 noted that vitreous changes were absent h isto logically with minimal cryosurgery burns, while heavy and large cryo applications did lead to definite vitreous strand formation. Clinically, other complications associated with heavy retinal cryopexy include macular pucker, exudative retinal detachment, and cystoid macular edema.16 The etiology of the retinal detachments in the rabbits we treated could have been secondary to either exudative retinal detachment, or possibly a change in the physical characteristics of the vitreous overlying the retinal tear leading to vitreal traction and liquification. Further long-term and histopathologic studies are pending.
If one assumes an incidence of 7,600 sclera! perforations during strabismus surgery annually in the United States it is of interest, therefore, that only a half dozen or so rhegmatogenous retinal detachments have been reported in the American literature in the past 23 years following such an event. This would seem to indicate that the chance of developing a rhegmatogenous retinal detachment following simple scierai perforation appears to be extremely small, perhaps less than one chance in ten thousand. The incidence of development of endophthalmitis is probably as great or greater than the development of retinal detachment. Knobloch and Lorenz17 retrospectively reviewed 300,000 operations and reported 87 cases of endophthalmitis and only eight cases of retinal detachments developing as complications in these patients.
In addition, our study determined that retinal cryopexy did not prevent the development of a retinal detachment, in fact, very heavy cryocoagulation, as might be applied by a surgeon unfamiliar with the technique, actually increased the risk of detachment of the retina. Thus, should an inadvertent perforation of the globe occur during strabismus surgery, it is certainly incumbent upon the surgeon to follow the patient carefully in the postoperative period. But unless a deranged vitreous is already present preoperatively such as in aphakia, high myopia or Marian's syndrome, or massive intravitreal hemorrhage occurs, no treatment to prevent rhegmatogenous retinal detachment appears to be indicated. Since four out of five of the retinal detachments that developed following strabismus surgery occurred many years later, it would appear reasonable to follow these patients in whom scierai perforation occurs postoperatively with sequential indirect ophthalmoscopy. Should signs of vitreous traction develop, appropriate prophylactic measures to prevent a retinal detachment can then be undertaken. In addition, since the majority of solerai perforations apparently are unrecognized by the surgeon at the time of the initial operation, it would also seem advisable to examine all patients undergoing strabismus surgery with indirect ophthalmoscopy postoperatively and should signs of a scierai perforation be noted the patient should be followed in the same manner. Finally, because of the danger of endophthalmitis, should the surgeon recognize a scierai perforation during the time of strabismus surgery, it would seem appropriate to culture the affected area, administer prophylactic antibiotics either topically, subconjunctivally, or systemically, and observe the patient very closely in the immediate postoperative period.
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15. Kirkconnel WS, Rubin ML: Effect of cryopexy on the vitreous. Arch Ophthaimol 1965; 74:399-402.
16. Goldbaum MH; Photocoagulation and cryopexy, in Peyman GA, Sanders, DR, Goldberg MF: Principles and Practice of Ophthalmology. Philadelphia, WB Saunders Co, 1980, vol II, p 1131.
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