Single minimal conjunctival incision for rectus muscles: a pilot feasibility study

Abstract

Background:

Small conjunctival incision size is desirable in strabismus surgery under topical anesthesia.

Objective:

To study the feasibility and tolerability of a small bulbar conjunctival incision (SB).

Design:

Non-randomized feasibility pilot study.

Methods:

After applying a 5-0 PGA (polyglycolic acid) traction suture, we did a 3–4 mm single conjunctival incision posterior and parallel to the rectus muscle insertion. A hang-back recession was done (6-0 PGA suture), and the conjunctiva closed (8-0 PGA suture). The outcome measures were feasibility, tolerability, and motor result.

Results:

Twenty-five patients were included. The median pain scale score was 3/10, and the satisfaction Net Promoter Score was 72. Mean duration of a recession was 12 min (range: 9–14 min). Mean duration of inflammatory signs and hemorrhage were 2.2 days (95% CI, 1.4–2.9), and 8.5 days (95% CI, 7.1–9.9), respectively. Distance deviation at 2 months was 3.1 Prism Diopters (95% CI, 1.5–4.5).

Conclusion:

SB is feasible and well tolerated for extraocular rectus muscle surgery.

Introduction

The three most common conjunctival incisions used for strabismus surgery are the fornix, limbal, and Swan bulbar incisions.^1–3 Strategies to reduce incision size have been used,^3–5 especially under topical anesthesia. A limbal incision may cause postoperative discomfort and increase the risk of dellen and anterior segment ischemia. Parks introduced a cul-de-sac fornix incision. ³ In fornix incision, conjunctival suture may not be required, and the postoperative scar is small or inapparent, but can be difficult to tolerate under topical anesthesia. Gobin and Bierlaagh described two small radial openings next to the rectus muscle insertions. ⁴ Mojon refined this technique and introduced the term minimally invasive strabismus surgery (MISS) for a muscle approach through small, parainsertional conjunctival openings. ⁵ This technique was subsequently applied to all types of strabismus surgery, including rectus muscle reoperation, rectus muscle transposition, oblique muscle recessions, and posterior fixation.^6–11 MISS minimizes tissue disruption, can reduce complications, and permits faster recovery, with the disadvantage of a long learning curve, increased surgical times initially, and higher incidence of scleral perforation, especially during the initial learning period. More controlled evidence, especially regarding alignment outcomes, is necessary for MISS. ¹²

Swan described a large conjunctival incision parallel to the limbus, behind the muscle insertion, lying almost in the fornix (original description). ¹ It has been associated with bleeding and postoperative scarring, especially when made over the muscle’s insertion. We tested the feasibility, tolerability, safety, inflammatory response, and preliminary outcome (short-term motor outcome) of a small single bulbar conjunctival modified type of Swan incision (SB).

Subjects and methods

We conducted a non-randomized feasibility pilot study. Criteria used for inclusion were: patients requiring rectus muscle surgery between 2021 and 2023, who had no previous surgery, non-restrictive and non-paralytic strabismus, horizontal deviation < 40 PD, and vertical deviation <25 PD (Table 1). Exclusion criteria were previous diagnosis of hypertension, diabetes, treatment with oral NSAID, or anticoagulant therapy.

Table 1.

Characteristics of participants.

Type of strabismus	n	Age	Sex (F)	VA lines of difference	SE	Preop deviation PD	Muscles op	Anesthesia	Postop deviation PD
Nonrefractive late-onset ET	3	6.3	1	0.6	+0.50	28.3	MR (2)	G	3.3
Age-related distance ET	7	59.4	3	1	+0.50	30.7	MR (2)	T	5.14
Partially accommodative ET	5	6	2	1	+2.75	24	MR (1–2)	G	2.4
SO palsy/vertical nonfusional diplopia	3	38	2	0.6	−0.50	17	SR (1)	T	3.3
Acute comitant ET	4	27	2	0	−1.00	25	MR (2)	T/S	3.05
Intermittent/constant Exotropia	3	15.6	2	0	−1.00	30	LR (2)	G	2.6
Total	25	29.3 (20.1 to 38.6)*	12	0.7 (0.3 to 1.04)**	+0.25 (−0.75 to +2.25)*	26.4 (23.9 to 28.9)*	1–2	G, T/S	3.04 (0.5 to 4.5)*

ET, esotropia; F, females; G, general; LR, lateral rectus; MR, medial rectus; PD, prism diopters; S, sub-Tenon’s; SE, spherical equivalent; SR, superior rectus; T, topical; XT, exotropia; VA, visual acuity.

^*Mean (95% CI).

^**Median (range).

The study was approved by the Institutional Review Board (Research Ethics Committee for Drugs, Hospital Ramón y Cajal; Universidad Autónoma de Madrid 238/23; ClinicalTrials.gov NCT05987878), and adhered to the Declaration of Helsinki. Written informed consent was obtained from patients or their parents/guardians. Preoperative clinical examination included VA (Precision Vision, Woodstock, IL), prism and cover test, evaluation of ductions and versions, Lancaster red-green test in cases of diplopia, anterior and posterior segment, and cycloplegic retinoscopy/auto-refractometry, 30–40 min after two drops of cyclopentolate, 5 min apart, in children.

General anesthesia was chosen for children, and adults who could not cooperate, and topical/sub-Tenon’s anesthesia was used in adults who were able to cooperate. A 5-0 PGA traction suture was placed near the corneal limbus. A 3–4 mm single conjunctival incision, 2 mm posterior and parallel to the insertion, in the medial, lateral, or superior rectus muscle, was used. The limit of muscle recession for inclusion in this study was 6 mm (medial rectus), 8 mm (lateral rectus), and 6 mm (superior rectus). Although a muscle hook was used for conjunctiva and Tenon capsule retraction, the muscle itself was not placed on a hook. For this, adequate exposure of the target muscle is necessary, with 5-0 PGA traction suture passed partial thickness through the sclera, 2 mm posterior to the limbus, in front of the target muscle insertion, used to retract the eye into a satisfactory position. A hang-back recession of the muscle was done using a 6-0 PGA suture. The sutures were pulled forward, pulling the rectus muscle up to the insertion. The calipers were set for the desired amount of recession (plus 0.5 mm to account for the distance between the scleral tunnels). The distal caliper tip was positioned against the anterior aspect of the insertion where the sutures exited the sclera. The sutures were clamped with a needle holder at the proximal caliper tip. Three overhand knots (3-1-1) were placed at this position and the sutures were cut. The muscle was then allowed to retract so that the knot was seated on the insertion. The conjunctival opening was sufficient to check muscle recession. The conjunctiva was closed by an 8-0 PGA single stitch (with knot burial; Figure 1).

Figure 1.

Recession of the medial rectus muscle (left eye). A PGA 5-0 traction suture is applied. Using a 3–4 mm conjunctival incision, 1–2 mm posterior to the muscle insertion, a partial thickness horizontal transverse pass, and additional full-thickness locking passes at the borders are made on each side of the muscle, with PGA 6-0 double needle suture (Alcon^®) ((a)–(d)). A hang-back recession is made, and the conjunctiva is closed with a PGA 8-0 single stitch (Alcon^®) ((e)–(f)).

PGA, polyglycolic acid.

We evaluated pain during the procedure using a 1–10 visual scale in 14 patients, operated with topical anesthesia (n = 10) or topical/sub-Tenon’s anesthesia (n = 4). Value was assigned by the patient according to pain experienced (0–3, no or mild pain; 4–7 moderate pain; 8–10 severe pain). The Net Promoter Score (NPS) satisfaction survey was conducted on all participants or their parents/guardians, in which patients gave a score of 1–10 depending on their satisfaction with the procedure. The NPS was obtained by subtracting the number of detractors (score 0–6) from the number of promoters (score 9–10), divided by the number of responders, and multiplied by 100.

Antibiotic/anti-inflammatory (Tobradex^®) and lubricant drops (Hyabak^®) tid were prescribed after surgery, for 2 weeks. All patients were examined postoperatively every third day during the first two weeks and at 1 and 2 months.

The main outcome measures of the study were feasibility, tolerability, and safety, estimated by pain scale score, satisfaction survey, duration of inflammatory signs (injection/hyperemia and/or chemosis), and hemorrhage. The secondary outcome was short-term motor alignment (at 2 months). Statistical analysis was conducted using SPSS version 29 (Armonk, NY, USA). We used mean (95% CI) for a description of normally distributed variables and median (range) when the distribution was not compatible with normality.

Results

We operated on 25 patients using the described incision (Table 1), under general anesthesia (n = 11), topical anesthesia (n = 10), and topical/sub-Tenon’s anesthesia (n = 4).

The rectus muscles were easily grasped and exposed, visibility was good, and the surgery was completed successfully. Mean duration of a single muscle recession was 12 min (95% CI: 11.2–12.6) with a range of 9–14 min. Gross visible scarring was not apparent in patients of the study group. The median incision size measured at the end of the procedure (before suturing) was 4.5 mm (range: 3.5–5.5 mm). Consequently, additional sutures (i.e., two interrupted sutures or a small continuous suture) were required in two patients.

Range of recessions was 3.5–5.5 mm in the medial rectus, 5.5–7.5 mm in the lateral rectus, and 3.5 mm in the superior rectus (only one case was included, enough dissected off the superior lid retractors). On average, 1.8 muscles were operated per patient.

The median pain scale score in the study group was 3/10 (range 3–5/10).

The NPS satisfaction survey yielded a score of 72 (optimum to excellent score).

Mean duration of conjunctival inflammatory signs (injection, hyperemia, or chemosis) was 2.2 days (95% CI, 1.4–2.9), and the duration of hemorrhage reached 8.5 days (95% CI, 7.1–9.9) (Figure 2).

Figure 2.

Preoperative (a) and postoperative appearance on day 1 (b), day 7 (c), and day 13 (d) and (e), after medial rectus recession (5.5 mm) for nonrefractive late-onset esotropia (20 prism diopters at distance and near). Black arrows indicate the location of the incision.

Average distance deviation measured 2 months after surgery (alternate prism and cover test) was 3.1 PD (95% CI, 1.5–4.5). Participants included in this preliminary study did not require reoperation during the follow-up period.

Discussion

We describe a small conjunctival incision, 2 mm posterior to the muscle insertion, with relatively easy and fast access to the muscle. Median time of surgery for a single muscle is 12 min. The incision is placed posterior to the muscle insertion to minimize bleeding. The use of bulbar incisions has been discouraged due to potential visible conjunctival scarring. The incision described by Swan was large and placed in the bulbar conjunctiva, “just anterior to the plica” for the medial rectus. ¹

A small bulbar conjunctival incision is feasible for extraocular rectus muscle surgery, particularly under topical anesthesia. Conjunctival scarring was not visible in participants during the follow-up period. In a few cases, incision size was enlarged by surgical manipulation of the conjunctiva, which required further suture and potentially could lead to a visible scar with time, in those cases. Because it is not necessary to pass a muscle hook for good exposure, and the incision is small, it is compatible with topical anesthesia. Although we did not compare SB to regular incision directly, our earlier experience indicates that pain with minimal incision in this study was usually in the lower limit of pain range observed with regular incisions (range: 4–6). Fornix incision provides good aesthetic results, but may not be tolerated with topical anesthesia in some patients. We established a limit for muscle recessions in the proposal of the study (6 mm for medial and superior rectus, and 8 mm for lateral rectus muscle) because we were not sure about adequate exposure for larger recessions. Although our experience indicates that larger recessions are feasible, we cannot recommend doing them using this incision for the moment.

Using different anesthetic modalities in different types of strabismus is a source of heterogeneity in this study, but increased the sample size to extend the applicability of SB.

Duration of inflammatory signs and conjunctival hemorrhage was relatively short. Horizontal rectus muscle surgical wounds remain in the interpalpebral space, which may result in longer visible inflammation and hemorrhage than vertical muscle surgery. Only one case with superior rectus surgery was included in the treatment group.

Two minimal incisions for strabismus surgery have been advocated on each side of the muscle, with less exposure in each of them, a MISS technique.^4,5 MISS technique was similar to the fornix approach in the early postoperative period regarding VA, conjunctival inflammation, and operating time in pediatric horizontal strabismus surgery.^13,14 Regarding postoperative recovery, the MISS and fornix approach could be similar to our small bulbar incision, but we did not compare the different types of conjunctival incision.

A limitation of this study is that we did not include a power analysis and calculation of sample size, but a formal sample size/statistical power calculation is not usually considered necessary in a pilot (feasibility) non-hypothesis testing study based on descriptive statistics and precision of estimates (CI). ¹⁵

The main advantage of the described incision is that access to the muscle is direct, relatively fast, and easy, with only one conjunctival incision, and is compatible with topical anesthesia.

In conclusion, this study indicates that a small bulbar conjunctival incision is a feasible, safe, and tolerable approach for rectus muscle surgery, especially under topical anesthesia, but we report preliminary data in a small group of patients. Generalization of these results requires larger prospective studies, with the inclusion of a control group, to confirm these findings.

Limitations

We report preliminary data on the use of a single conjunctival incision for surgery of rectus muscles in a small group of patients. Conclusions cannot be generalized until prospective controlled studies are conducted. Another limitation is that we did not include a formal power analysis and calculation of sample size, although it is not usually considered necessary in a pilot (feasibility) non-hypothesis testing study based on descriptive statistics and precision of estimates.