The change of the extraocular muscle insertion after a slanted recession in rabbit eyes

Slanted recession on bilateral lateral rectus for the treatment of intermittent Exotropia with convergence insufficiency

Purpose

To evaluate the efficacy and safety of slanted bilateral lateral rectus recession (S-BLRc) for the treatment of convergence insufficiency-type intermittent exotropia (CI-IXT) in children and to probe the relationship of the slanted amount and surgical outcomes.

Methods

Retrospective study. Fifty-eight patients with CI-IXT, aged 4 to 10 years old, underwent S-BLRc procedures. According to the different slanted amount between the upper and lower poles of lateral rectus, all the patients were grouped: Group A (slanting 1 mm, n = 22), Group B (slanting 1.5 mm, n = 18) and Group C (slanting 2 mm, n = 18). The successful surgical outcome was defined as deviation in the primary position ranging from exotropia< 8^△ to esotropia< 5^△ both at near and at distant as well as the near-distance difference (NDD) < 5^△. We analyzed and compared the preoperative and postoperative data including deviations both at near and at distance, NDD, objective torsion, horizontal deviation at up and down gaze, lateral incomitance, binocular vision and surgical success rate among three groups.

Results

The average deviations were significantly decreased from − 37.1^△ ± 4.2^△ (−,exotropia) to − 1.4^△ ± 4.6^△ at near (P < 0.05) and from − 25.8^△ ± 3.7^△ to − 0.1 ± 4.1^△ at distance (P < 0.05). The postoperative NDD on average was significantly reduced from 10.0^△ to 1.8^△ in Group A (P < 0.05), from 11.2^△ to 0.8^△ in Group B (P < 0.05) and from 13.3^△ to 0.9^△ in Group C (P < 0.05). There was a significant difference in the mean corrections of NDD among the three groups (8.2^△ in group A, 10.3^△ in group B and 12.4^△ in group C respectively, P < 0,05). All the patients attained various improvement of stereopsis after surgery. None had torsional diplopia, A-V pattern and lateral incomitance after strabismic surgery. Totally, the surgical success rate was 89.7% in our series at the 6- to 8-month follow-up.

Conclusions

Slanted bilateral lateral rectus recession is an effective and safe procedure for the treatment of CI-IXT in children. S-BLRc can successfully collapse exotropia both at distance and at near, decrease NDD and benefit to gain binocular vision. The correction of NDD was associated with the slanted amount.

Adhesion after Y-split procedure can affect its mechanism for treating overshoots in Duane's syndrome

PURPOSE

To investigate the extent of adhesion and changes in the Y configuration after the Y-split procedure, compared with the posterior fixation suture.

METHODS

Twelve New Zealand white rabbits were included in the study. The 10-mm Y-split procedure was performed in the superior rectus muscle (SR) of one eye, and the 10-mm posterior fixation suture was made in the SR of the other eye. Six weeks after surgery, the Y arm lengths and lengths of adherence to the sclera were measured. If the adhesion involved the whole Y arm, the distance between the original SR insertion and most proximal part of the adhered SR was measured. In the eyes with posterior fixation suture, the distance between the SR insertion and most proximal part of the adhered SR was evaluated.

RESULTS

The average nasal and temporal Y arm lengths were 6.37 ± 0.65 and 6.54 ± 0.63 mm, respectively, a significant decrease from those measured immediately after surgery (P = 0.002 and 0.002, respectively). Adhesions involved the entire Y arms in 11 of 12 SRs (91.7%), with an average adhesion length of 7.01 ± 1.04 mm. In SRs with posterior fixation sutures, the average adhesion was 9.18 ± 0.62 mm from the insertion, which was only 2.17 mm posterior to proximal portion of adhesion in Y-split SR (P < 0.001).

CONCLUSIONS

Healing process reduces the Y arm length. Adhesion may involve the entire Y arm and could weaken or alter the therapeutic mechanism after the Y-split procedure.

Spontaneous Reattachment of the Medial Rectus After Free Tenotomy

PURPOSE

To assess the outcome of free tenotomy of the medial rectus muscle in post-natal monkeys.

METHODS

The medial rectus muscle was disinserted in both eyes of 6 macaques at age 4 weeks to induce an alternating exotropia. After the impact on the visual cortex and superior colliculus was investigated, the animals were examined post-mortem to assess the anatomy of the medial rectus muscles.

RESULTS

After tenotomy, the monkeys eventually recovered partial adduction. Necropsy revealed that all 12 medial rectus muscles had reattached to the globe. They were firmly connected via an abnormally long tendon, but at the native insertion site.

CONCLUSIONS

Medial rectus muscles are able to reattach spontaneously to the eye following free tenotomy in post-natal macaques. The early timing of surgery and the large size of the globe relative to the orbit may explain why reinsertion occurs more readily in monkeys than in children with a lost muscle after strabismus surgery. [J Pediatr Ophthalmol Strabismus. 2018;55(5):335-338.].

Change in the location of the equator and recessed muscles in young rabbit eyes

PURPOSE

To study the changes in the location of the equator and the new insertion of extraocular muscle after recession surgery in a rabbit model.

METHOD

An experimental study was performed in ten eyes of five rabbits. Eyes were divided into two groups according to the amount of recession. In right eyes, 5 mm superior recti (SR) muscle recession, approximately 2 mm posterior to the equator, was performed (5 mm recession group), while in the left eyes, 3 mm recession was performed to the location of the equator (3 mm recession group). We measured the distance of the equator from the limbus, as well as the distance between the superior rectus insertion and the equator. The preoperative measurements were compared with the results 2 months after the surgery. The change in location of the superior rectus and the equator was compared between the two eyes.

RESULT

The recessed SR muscle did not show any significant change in location in both groups (p = 0.18 and 0.16 respectively). However, the location of the equator of rabbit eye showed movement of about 1 mm posterior to the initial location with the growth of the eyeballs (p = 0.04 and 0.03, respectively).

CONCLUSION

The location of the equator moved posteriorly at 2 months postoperatively in young rabbit model while the insertion of the recessed SR did not show any significant movement.