Clinical Analysis of restrictive strabismus secondary to ophthalmic surgery

Background: This study aimed to report the clinical characteristics and surgical methods of restrictive strabismus secondary to ophthalmic surgery. Methods: This retrospective case series covered 14 restrictive strabismus cases secondary to ophthalmic surgery. After evaluation of the clinical history and the basic ophthalmological ndings, the following parameters were examined: squint angles (prism with alternative cover test, Krimsky’s test or Maddox cross), ocular motility, duction test and the forced duction test. All paitients underwent surgery, the strabismus surgery included the excision of adhesions and scar tissue, adhesiolysis, medial and lateral ligaments separated, repositioning of extraocular muscles (according to the degree of deviations). We described the clinical characteristics and evaluated the surgical results in strabismus eyes. Results: All patients were satised with the results of surgery, obtained anatomical reduction and partial functional recovery. In nine cases with preoperative diplopia, eight cases had no diplopia after surgery and one patient’s diplopia disappeared after the secondary surgery. The other ve cases without preoperative diplopia, but had restricted ocular motility, which improved signicantly than before surgery. Conclusions: Orbital surgery, trauma, conjunctival surgery, strabismus surgery and so on, can lead to secondary restrictive strabismus surgery. Strabismus surgical treatments including the full removal of the muscles around the scar, adhesiolysis, medial and lateral ligaments separated, eye muscle surgery, can provide excellent results and patient’s satisfaction.


Background
Secondary restrictive strabismus is unconcomitant strabismus, due to the mechanical action of adherences between extraocular muscle and surrounding connective tissue, conjunctival and moderate ligament, bulbar conjunctival scarring after pterygium excision [1], cosmetic wide conjunctivectomy [2], scleral buckle procedure [3], and orbital surgery [4][5][6][7][8], limited the eyeball movements and generated strabismus. Its mechanisms include sensory disturbances after surgery, surgical scars, bleeding, direct muscle injury, myotoxicity caused by the injection of local anesthesia or antibiotics, abnormal position of restrictive extraocular muscles caused by implants, and so on [2,[9][10][11]. It has aroused the attention of ophthalmologist because of its complexity. Clinical manifestations include diplopia, dyskinesia, abnormal movement, anisometropia and compensatory head position. If it occurs in children childhood, can also lead to amblyopia. The overall incidence of secondary restrictive strabismus has not been reported. The corrective surgery has its di culty and there is no report about the surgery choice and speci c methods of the surgery. Therefore, this article retrospectively analyzes the clinical data of the patient diagnosed secondary restrictive strabismus after ophthalmic surgery in our hospital during April 2015 to September 2015, and analyzed its causes, clinical features and surgical methods.
Materials And Methods 1. General Information: The study included 14 patients (6 women and 8 men) with a mean age of 32.7 years,patients were followed up for 3 months. 14 cases of secondary restrictive strabismus, in which include 2 cases secondary to thyroid orbitopathy surgery and strabismus surgery, 4 cases secondary to orbital fracture surgery, one case secondary to orbital tumors surgery, 3 cases secondary to strabismus surgery, one case secondary to conjunctivochalasis surgery, two cases secondary to conjunctival trauma suture surgery, one case secondary to traumatic cataract surgery. The recruitment and research protocols were reviewed and approved by the Institutional ethics commission.
2. Methods: After evaluation of the clinical history and the basic ophthalmological ndings,the following parameters were examined: squint angles (prism with alternative cover test, Krimsky's test or Maddox cross), duction test and the forced duction test monocular and binocular movements and the characteristics of strabismus. All included patients had ophthalmologic motility exams testing ductions of each eye in four cardinal gaze positions: abduction, adduction, supraduction, and infraduction. Motility in each gaze position was graded on a commonly used scale of 0 to − 4, with 0 signifying no restriction and − 4 indicating an inability to pass the midline in a particular direction. The remaining points on the scale represent further reduction in approximately 25% increments in between normal motility and inability to pass midline [12]. Figure 1 depicts an example of this motility scale for supraduction.
Duction test and the forced duction test to examine the ocular motility, eyeball movements limited level: (1) mild: some limited movement in a direction independent, passive stretch of the eye can place; (2) moderate: a direction completely independent movement restricted when the eye can not be completely passive stretch in place; (3) severe: passive stretch completely restricted. All preoperative clinical data of included patients is shown in Table 1. 4. Surgical methods: The strabismus surgery included the excision of adhesions and scar tissue, adhesiolysis, disconnection of medial and lateral ligaments, reposition of extraocular muscles (according to the degree of deviations).

Results
1. Extraocular muscle and its around connective tissue adhesions, conjunctival scarring were seen in patients surgery, some of them accompanied by muscle atrophy and brosis. Two cases secondary to the rst strabismus surgery were accompanied by adhesion of lateral rectus (LR) and inferior oblique (IO) muscle.
2. All 14 patients showed a preoperative horizontal squint angles range of 100 to 20 PD, average 39.8 PD, vertical squint angles is range of 20 to 8 PD, average 12.2 PD. Postoperative horizontal squint angles averaged 3.1PD, squint angles averaged 0.9 PD. 13 patients achieved good results after the rst surgery, and 1 patient obtained good results after the secondary surgery. All patients were satis ed with the results of surgery,obtained anatomical reduction and partial functional recovery. In nine cases with preoperative diplopia, ve cases had no diplopia in full eld after the rst surgery, three cases had no diplopia in functional eye position (in primary position and down reading gaze), one patient's diplopia disappeared after the secondary surgery. The other ve cases without preoperative diplopia, but had restricted ocular motility, which was improved signi cantly after surgery (Table 2).

Discussion
Of acquired restrictive strabismus mainly because of extraocular muscle lesions occur around the eye or orbit organized adhesions or abnormal strips contain other restrictions affecting the normal rotation of the eye. Restrictive strabismus secondary to surgery is one of a variety of complications, it is due to injury, the wound dry and surgical ischemia and other reasons, resulting in extraocular muscle and its surrounding tissue adhesions, brosis, mechanically limiting eye movement, cause insurmountable diplopia, affect normal life and work of patients. Secondary restrictive strabismus should be differentiated from extraocular muscle paralytic strabismus. Restrictive strabismus can be caused by conjunctival scarring, fat adherence syndrome, or rectus muscle contracture,and so on [13]. The fat adherence syndrome is an important cause of restrictive strabismus after retina surgery and that this complication can be minimized by avoiding surgical maneuvers that violate Tenon's capsule and expose extraconal fat. Many factors affected the longterm effects of strabismus surgery, which is very important reason is that the movement disorders caused by scar adhesions after surgery [4]. If restrictive strabismus in children early age, it will affect visual acuity and binocular vision development, and lead to monocular amblyopia in severe case. The treatment of secondary restrictive strabismus includes: prism, Botox injections or surgery [14]. Furthermore, some additional treatments were applied to avoid recurrency (subconjunctival and topical corticosteroids, amniotic membrane and therapeutic contact lens, 15).
In this study, strabismus surgical treatments including the full removal of the muscles around the scar, adhesiolysis, separation of medial and lateral ligaments and eye muscle surgery, have provided excellent results and patient's satisfaction. Among 14 patients, one case (No. 4) which surgery only including the full removal of the scar around the muscles, adhesiolysis, separation of medial and lateral ligaments, corrected small degree oblique; one case (No. 2) which the above surgery combined with antagonistic muscle surgery, diplopia in function eye position was disappeared after surgery; one case (No. 10) we only resect the scar around muscles, decomposed adhesions, corrected strabismus. The other 11 patients were used the full removal of the scar around the muscles, adhesiolysis, medial and lateral ligaments separated, and eye muscle surgery. During surgery we have found that limited scar around muscle is limiting eye movements, the duction and forced duction test is positive. After surgery, muscle adhesion has released and signi cant recovery of the eye movement is obtained. When combined with the corresponding eye muscle surgery, the amount of muscle operation with experience is very different with the conventional amount, therefore, it is convenient and helpful to have surgery under local anesthesia, which can observe eye position during the operation and improve the success rate of the corrective surgery. Six cases involved with medial rectus muscle surgery were found had closed adhesion of temperance canthal ligament and medial rectus, muscle function is limited severely. We believe that the rst surgery failed to fully separate control ligament and medial rectus, results in dysfunction and eye movements restricted.
Our experience suggests that the full separation between internal control canthus ligament and medial rectus plays a vital role in lifting restrictions and functional recovery for the medial rectus surgery.
In this study, 3 cases get restrictive strabismus secondary to strabismus surgery, preoperative examination indicates that the non-common factors have occurred in patients with severe strabismus and eye movement is not in place. It prompts us should operate carefully during strabismus surgery to reduce adhesions, including non-injury anatomy, muscle envelope to protect the integrity, complete hemostasis, minimize burning, to avoid interference Tenon's fat pad when cut, to avoid fat adhesion syndrome, but also to avoid over-stretch the extraocular muscles or muscle stripped from the surface of the eye [16], to avoid postoperative non-common factors. Such patients, if conventional surgery design, it is di cult to achieve the desired effect, we use the above procedure, the patient eye position corrected, eye movement improved.

Conclusions
In summary, the improper operation of eye surgery, can lead to secondary restrictive strabismus. The scar tissue ablation, adhesiolysis, separation of lateral and medial control ligament of muscle combined with muscle surgery can correct eye position, improve eye movements, eliminate diplopia and remove the compensatory head position, is an effective surgery choice. In this study, due to time constraints, sample collecting is small, which remains further study.