Misalignment of eyes have a negative impact on an individual’s psychosocial functioning leading to poor performance, lack of interpersonal relationships, job security, self image, as well as having an inferiority complex and poor binocular fixation. Large angle exotropia is described as an angle ranging from 35 to 60 prism diopter (PD).[2-4] Aetiology includes primary, consecutive and trauma. Strabismus surgery helps the visual axes to line up and to abolish associated double vision and improve stereopsis. It has been established that the binocular vision following realignment of eyes can be restored in adults having long standing strabismus.
Two horizontal Recti muscles correction for exodeviation
in a single operation rectifies large
angle exotropia up to 50 PD with minimal occurrence
of symptomatic asymmetric deficit of ocular
movement and greater patient’s contentment.
However, larger trials are required to establish
There are limited studies and debate is ongoing regarding the best treatment for additional large angle exotropia. Correction among latest studies involves two surgical techniques; large lateral rectus recession bilaterally (if good visual acuity in both eyes) and maximal recession resection procedure unilaterally (if one eye is amblyopic). However, the drawback of correcting unilateral large angle two muscles is the potential hazard of surgically causing a symptomatic lateral asymmetrical incomitance. Precise success criteria varies with many surgeons considering motor outcomes merely, with ocular coalition of ± 5 to 15 PD surgically[2,9] and successful surgical accomplishment ranging from 42.9% to 88.2%.[3,4] Recession of a lateral rectus muscle greater than 7 millimeters may lead to significant abduction deficits, therefore several ophthalmologist operate on two horizontal recti muscles and correct remaining divergence with subsequent procedures having capricious outcomes, whereas, other ophthalmologists consider concurrent surgery four horizontal recti muscles to be a better approach.[10,11] This study shared the surgical experience of one-stage two horizontal recti muscles surgery for large angle exotropia to optimize the primary position alignment and to minimize symptomatic iatrogenic postoperative horizontal incomitant deviations.
This study was conducted at Khalid Eye Clinic, Nazimabad, Karachi, from 1st February 2019 till 30th September 2019 with a follow up period of three months post operatively. Thirty patients with an age range from 18 to 30 ± 5.4 years with manifest large angle exotropia between 40 PD to 50 PD underwent surgical correction. Prior to the surgical correction, a proforma was used to record the history and examination of each patient such as presence of any similar or other ocular complains within the family, onset age, previous surgery and the age at that time, visual acuity with best correction, cycloplegic refraction, ocular alignment before the surgery at distance and near, preoperative ocular motility, post operative diplopia test, A or V pattern abnormality, existence of dissociated vertical deviation (DVD) and any previous conservative or surgical interventions. For cases with significant amblyopia, the surgery was done on the amblyopic eye. The exclusion criteria included exotropia of <40 PD or >50 PD, occurrence of neurologic discrepancy, simultaneous presence of restrictive or paretic squint, past history of surgical correction of strabismus. Each patient was requested to fill an informed consent prior to participation in this study. In the present study, unilateral recession of the lateral rectus with resection of the medial rectus for an exotropia of 40 PD to 50 PD was performed. Per operative forced-duction test was performed in all participants. All surgeries were done by one surgeon (QQ) and examination carried out by one (ZK) of the co-authors. Subsequent postoperative follow-up period was up to three months. Ocular alignment pre and post operatively were evaluated via cover, uncover and alternate prism cover test (distance of 6 m in principal and cardinal positions of gaze) whereas, motor alignment was evaluated (at 33 cm, near) with the help of spectacle adjustment. All of the 30 patients underwent lateral rectus recessions of 10 millimeters or greater and medial rectus resection of upto 6.5 millimeters. Surgery was performed via limbal approach on all the surgeries. Patients underwent a recession and resection procedure on the poorer seeing eye when they had a significant difference in vision between the two eyes. If divergence was within 10 PD of exotoropia, orthophoria was supposed to be present. For the evaluation of surgical accomplishment, ocular alignment was made the criteria and surgical success was measured with the participant having orthophoria for near and distance following 90 days of the surgical procedure. Those who failed to meet the surgical accomplishment criteria were taken as poor result. Factors responsible for poor result comprised of age at onset and at the time of surgery, degree of divergence, period of divergence, presence of concurrent amblyopia or anisometropia, abnormal function of the oblique muscle, immediate post operative deviation on the following day and the surgical technique carried out. The aim of this surgery is to achieve optimum ocular alignment in a single stage, two horizontal recti muscle surgery thereby improving psychosocial functioning and limiting any subsequent symptomatic horizontal incomitant deviation. Data analysis was done on statistical package for social services (SPSS) 22.0. Approval was obtained from the institution’s Ethical Review Committee.
This study included thirty patients of both genders with a preponderance of females at 70%. Out of the thirty patients, 21 eyes (70%) underwent surgical correction of the right side. 27 (90%) out of the 30 patients resulted in orthophoria with a deviation within 10 PD at the end of the three month follow up period (Picture 1). 3 eyes (10%) resulted in undercorrection and required further surgical correction the fellow eye. Two (6.6%) out of the 30 patients developed surgical granuloma at the site of conjunctival incision and were treated in the follow up period. Two (6.6%) out of the 30 patients complained of ocular discomfort and watering which was treated conservatively by medical therapy. There were no motor deficits in either of the cases.
Surgically adjusting large angle exotropia is a challenge with no general consensus regarding an unsurpassed surgical technique. Criteria for eligibility differ in literature when it comes to selecting the type of surgery, involving two, three, or four muscles. Satisfactory alignment comprises of residual exodeviation within 10 to 15 prism diopter of orthophoria.[11,12] This study aimed for a post operative orthophoria of being within 10 PD. Surgery involving two horizontal recti muscles is not as much invasive as three or four muscle surgical procedure and has a varying surgical accomplishment rate from 40 to 70%. Although this study is a small scale study but the study results showed that 90% of our patients had an acceptable cosmetic outcome and orthophoria within 10 PD. Several studies, such as, by Ganguly showed an accomplishment rate of 83.3% among adults with 40–80 PD of exodeviation following unilateral two horizontal recti muscle procdure, Livir-Rallatos observed that following unilateral two horizontal recti muscle recession and resection surgery, exodeviations of up to 50PD could be managed successfully at a rate of 71% which decreased to 18% for exodeviations more than 50PD and more recently, Talebnejad reported a good surgical achievement in 79.5% patients having exodeviation after undergoing unilateral supramaximal recession and resection with no resultant double vision in lateral gaze. Similarly, a study by Kumar observed an 87.5% surgical achievement within 10 PD with one patient having an undercorrection of 20 PD necessitating a subsequent corrective surgery. No complications were observed and concluded that single stage two horizontal recti muscle surgical procedure has a superior outcome for large angle exotropia of > 60 PD. This was in accordance with the present study. Another study by Kang mentioned that acceptable surgical outcomes after undergoing two horizontal recti muscle surgery can be achieved for exotropia of < 55 PD,whereas, with exotropia of > 55 PD, three horizontal recti muscle surgery is beneficial. Since, the definitive criterion of success is subjective patient satisfaction, in some cases surgical achievement may possibly not compare to patient’s contentment. Study done by Currie reported a greater patient satisfaction rate at 92.0% as compared to the 72.0% surgical accomplishment rate. Another study showed a similar outcome where patients were extremely content with the remaining discrepancy of more than 10PD on each side of orthotropia which appeared to be asthetically appealing. This study showed that 90% of the patients who underwent unilateral recess- resect procedure was satisfied with their cosmetic outcome. The surgical outcome in this study was similar to a study done by Schwartz, which showed a 77% accomplishment of postoperative alignment within 15PD and proposed that a two horizontal recti muscle surgery is adequate for large angle exotropia. A post operative motility deficit is sometimes associated but no limitation in the extraocular movements was found in this study. Persistent large angle exotropia has a noteworthy impact on a person’s psychological and social well being and remains a chief reason for seeking surgery. The aim of the surgical procedure is to align the eyes optimally with lesser amount of surgical interventions possible. This study emphasizes on the advantage of individualized single two horizontal recti muscle surgery.
Two horizontal recti muscles correction for exodeviation in a single operation rectifies large angle exotropia of up to 50 PD with minimal occurrence of symptomatic asymmetric deficit of ocular movement and greater patient’s contentment. However, larger trials are required to establish this.
Conflict of interest: None
Financial Disclosure: None
Funding: Self funde
3. Ectopia Lentis in a Patient with Homocystinuria
An infant had been diagnosed with homocystinuria She was found to have bilateral inferior sub-luxation of clear lenses. By age 9, the subluxation had progressively wors¬ened significantly. Her visual acuity was 20/63 in the right eye and 20/50 in the left. Broken zonular fibers are seen at the lens equator of the subluxated lens. Homocystinuria is an autosomal recessive inherited disorder of methionine metabolism due to deficiency of cystathionine beta-synthase. The zonule normally contains high levels of cystine, and a deficiency of this amino acid leads to in¬creased fragility of the zonular fibers, which then alters the lens stability
Deepa Taranath, Angela Chappell, Flinders Medical Centre Ophthalmology Department, Adelaide, Australia.