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Institute of Ophthalmology, JN Medical College, AMU, Aligarh, Uttar Pradesh, India

Correspondence to: Dr. A.K. Amitava, Prof. Strabismology, Institute of Ophthalmology, JN Medical College (Gandhi Eye Hospital campus) AMU, Aligarh, Uttar Pradesh, India. E‑mail: akamitava@gmail.com

Manuscript received: 22.02.12; Revision accepted: 27.08.12

Minimally invasive strabismus surgery versus paralimbal approach: A randomized, parallel design study is minimally invasive strabismus surgery worth the effort?

Richa Sharma, Abadan K Amitava, Sadat AO Bani

Introduction: Minimal access surgery is common in all fields of medicine. We compared a new minimally invasive strabismus surgery (MISS) approach with a standard paralimbal strabismus surgery (SPSS) approach in terms of post‑operative course. Materials and Methods: This parallel design study was done on 28 eyes of 14 patients, in which one eye was randomized to MISS and the other to SPSS. MISS was performed by giving two conjunctival incisions parallel to the horizontal rectus muscles; performing recession or resection below the conjunctival strip so obtained. We compared post‑operative redness, congestion, chemosis, foreign body sensation (FBS), and drop intolerance (DI) on a graded scale of 0 to 3 on post‑operative day 1, at 2‑3 weeks, and 6 weeks. In addition, all scores were added to obtain a total inflammatory  score  (TIS).  Statistical Analysis:  Inflammatory scores were analyzed using Wilcoxon’s signed rank test. Results:  On  the  first  post‑operative  day,  only  FBS  (P  =  0.01) and TIS (P  =  0.04) showed significant difference favoring MISS. At 2‑3 weeks, redness (P  =  0.04), congestion (P  =  0.04), FBS (P = 0.02), and TIS (P = 0.04) were significantly less in MISS eye. At 6 weeks, only redness (P = 0.04) and TIS (P = 0.05) were significantly  less. Conclusion: MISS is more comfortable in the immediate  post‑operative  period  and  provides  better  cosmesis in the intermediate period.

Key words: Cosmesis, incision, minimal, strabismus, surgery

Minimal access surgeries are common in almost all fields of medicine.[1] Phacoemulsifications, sutureless vitrectomies, minimal invasive lid surgeries, miniature implant drainage surgeries all involve a minimal access approach. Minimal access surgery allows an early rehabilitation with reduced hospital stay. If such an approach is possible in strabismus

and offers better post‑operative comfort with an equally successful outcome, in terms of alignment, as compared to the conventional strabismus surgery, it would provide a worthwhile alternative to the strabismus surgeon.

Conjunctival incisions in strabismus have traditionally been either the Harm’s limbal approach,[2] Park’s forniceal approach,[3] Velez single snip surgery,[4] and Swan’s approach.[5] Recently, Mojon has published numerous papers wherein he discusses what he calls as minimally invasive strabismus surgery (MISS). This essentially involves giving two radial almost parallel (though somewhat diverging) incisions parallel to the strap like rectus muscle, extending posteriorly from the upper and lower ends of the muscle‑sclera insertion. Most of his cases have been compared to historical controls operated via the limbal approach. These studies suggest that the MISS technique provides less post‑operative inflammation compared to the standard limbal approach.[6]

We undertook a parallel design study in cases undergoing bilateral symmetrical recession/resection, wherein one eye was randomized to the MISS approach while the other was operated via the standard para‑limbal approach, to compare post‑operative comfort and cosmesis.

Materials and MethodsAfter obtaining clearance from the institutional board of studies and informed consent, horizontal strabismus patients qualifying for symmetrical recession or resection surgeries on the horizontal rectii were included. Anesthesia utilized was either standard peribulbar block or general anesthesia (propofol and nitrous oxide). One eye was randomized (using an unbiased coin) to standard paralimbal strabismus surgery (SPSS) while the other automatically qualified for MISS.

After separating the lids with universal eye speculum, a 5‑0 silk traction suture (Johnson and Johnson Ltd. Aurangabad; NW 5079) was passed through the superficial sclera near the limbus at 12 and 6 o’clock to expose the quadrant of interest. Four points were marked on the conjunctiva: Two at the upper and lower ends of the rectus muscle insertion and two at the posterior limits of the planned para‑muscular conjunctival incisions [Fig. 1a]. The two points on each side of the muscle insertion were then incised with a Bard‑Parker blade (#11) after  raising a  fold of  conjunctiva by  lifting  the  conjunctiva between forceps, so as to obtain two incisions parallel to the upper and lower edge of the horizontal rectus muscles, with their anterior limits at the upper and lower ends of the muscle insertion [Fig. 1b]. The radial length of these incisions was 1 mm less than the planned recession/resection if the latter was ≤5 mm, and two mm less if  >5 mm. Using  blunt Wescott  scissors, careful dissection was carried out to identify the muscle edge, under which a muscle hook was then passed [Fig. 1c]. Further dissection then helped delineate the muscle and the adjacent sclera up to the site of recession. A similar conjunctival incision was made at the superior border of the muscle, aided by the muscle hook already placed below the muscle. Subsequently, the strap of conjunctiva, overlying the muscle tendon, between the two conjunctival incisions, was meticulously dissected free of the muscle up to the insertion to facilitate subsequent surgery in that area [Fig. 1d]. This provided us access to the upper and lower edge of the muscle right up to the insertion, as also the sclera/muscle till the point where recession/resection was to be

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carried out. The planned site of recession on the sclera, or the site of resection on the muscle, were marked [Fig. 1e].

For recessions: Vicryl 6‑0 (Johnson and Johnson Ltd. Aurangabad NW 2670) locking bites were taken from the muscle margins from near the insertion [Fig. 1f ] and the muscle disinserted using spring scissors [Fig. 1g] and anchored to the marked spot on the sclera [Fig. 1h]. Occasional cauterization achieved hemostasis. If the parallel conjunctival cut edges appeared to be in good apposition, no sutures were applied; else, a single central Vicryl 8‑0 suture approximated the incisions. Good apposition was considered wherein the edges were no more than 2 mm apart at a point of maximum separation, after gently smoothening the conjunctival surface [Fig. 1i]. In case of any complications, like excessive hemorrhage, or difficulty in suturing the muscles, were encountered, it was planned to prolong the conjunctival incisions towards the limbus and join them, effectively converting them to resemble the limbal approach; in such an event, the MISS approach would be considered to have failed.

For resection: After a similar conjunctival approach as for recessions, two Vicryl 6‑0 sutures were applied at the edges of the extra‑ocular muscle (EOM) at the point of desired resection and passed through the insertion of the EOM. The muscle between the suture bites was excised; tying the sutures brought the point of resection to the insertion, effecting a resection.

We recorded the duration of surgery (in minutes) from the start of the conjunctival incision to the completion of surgery. Post‑operatively graded scoring of inflammation (o to 3: Nil, mild, moderate, severe) was done by an observer masked to the randomization; on day 1, at 2‑3 weeks, and 6 weeks: Specifically redness, congestion (these two were compared to standard photographs), chemosis, foreign body sensation (FBS), drop intolerance were scored; and each score combined to yield a total  inflammatory score  (TIS; with a possible  range  from 0 to 15). Visible scarring (from one meter) and final alignment were noted at 6 weeks.

ResultsWe included 14 parallel designed surgeries on 10 patient;

10 were bilateral recessions, while 4 of subjects participated a

second time (3 months later) undergoing planned second bilateral recestions on account of large angles not amenable to single strabismus‑surgical correction. The demographic and other details are shown in table 1. The mean duration of surgery in the SPSS was 29.6 (SD ± 5.37) minutes as compared to 40.4 (SD ± 7.98) minutes in the MISS approach, with a mean difference of 10.8 minutes (95% CI for difference: 2.67 to 18.92 minutes.), which was significant (Wilcoxon test; P = 0.013). On the first post‑operative day,  there were significant differences (P < 0.05) in the median inflammatory scores  for FBS and TIS  (Wilcoxon test, Table 2). At 2‑3 weeks, in addition, significant differences for redness and congestion. By 6 weeks, significant differences were restricted to redness and TIS. At final follow‑up at 6 weeks, significant scarring was observed in all the eyes, which underwent SPSS while it was present  in 9 MISS eyes;  the difference was not statistically significant (Chi‑square, Fisher’s exact test; P = 0.09). There was no change in visual acuity postoperatively in any of the patients during any time in follow‑up. Amount of strabismus, target surgery, final alignment along with status of fusion, and stereopsis at 6 weeks postoperatively are also shown in table 1. No complication occurred in our series. Six of 14 cases of MISS eyes did not require conjunctival suture. Conversion was not required in any of the MISS eyes.

DiscussionWe compared post‑operative comfort and cosmesis, by MISS and SPSS, in patients undergoing symmetrical strabismus surgeries in a parallel design, randomizing one of two eyes, since that may be a superior model to compare inflammatory outcomes. On the first post‑operative day, there was no significant difference between the two eyes in terms redness, congestion, chemosis, and drop intolerance; only FBS (P value < 0.01) was significantly less in the MISS eyes. This could be on account of the small incisions and posterior placement of conjunctival sutures (if any) in the latter group.

At 2‑3 weeks follow‑up, scores for redness, congestion, and foreign body sensation were significantly less in the MISS eyes [Fig.  2]. While  at  6 weeks, we did not find any significant difference, except for redness and total inflammatory score [Table 2].

In his introductory paper, Mojon utilized the MISS approach and compared them with a historical group, which underwent

Figure 1: (a‑i) Figures showing surgical steps for MISS (recession) (see text)

d

ih

c

g

b

f

a

e

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Although we found 9 of 14 cases (64.3%) of MISS showing a significant scar at 6 weeks compared to all 14 cases (100%) of SPSS, the results did not reach statistical significance (Fisher’s exact; P Value: 0.09). Mojon has also commented in his comparative study that minimal cicatrization was seen along the incision line, which did not hinder free movement of the conjunctiva over the sclera. On occasion (sic), no scar was seen biomicroscopically.[6] Only larger studies with more statistical power may provide clear answers to this question.

In our study, MISS took significantly longer than SPSS; but, it is likely that this would decrease as experience with MISS accumulated. No researchers have addressed this question.

Although comparison of alignment by its very nature cannot be compared in a study like ours, we are reporting post‑operative alignment outcomes [Table 1], since that would be of interest to

Table 1: Demographic details of the patients along with post operative functional outcomes

Age in years/gender

Refraction (BCVA* in LogMAR)

Diagnosis Amount (PD)†

Target (PD)

Surgery Amount (mm)

Fusion (present)

Stereopsis (arc‑secs)

Post‑op alignment

(PD)

Residual angle (PD)

RE LE

20/m Plano (0.0) Plano (0.0) ET 50 50 BMR‡ 6 P 120 0 0

28/m Plano (0.0) Plano (0.0) ET 45 45 BMR 6 P 240 5 5

28/m Plano (0.0) Plano (0.0) ET 90 60 BMR 7 Absent Nil 45 15

20/f Plano (0.0) Plano (0.0) XT 50 50 BLR** 9 Absent Nil 10 10

17/f +0.50 (0.18) +0.50 (0.18) XT 75 60 BLR 10 Absent Nil 30 15

20/m +1+2.0×180 (0.3)

+1+2.0×110 (0.3)

ET 90 60 BMR 7 Absent Nil 40 10

14/f Plano (0.0) Plano (0.0) XT 45 45 BLR 8 P 120 0 0

17/f +2.50 (0.3) +2.50 (0.3) ET 95 60 BMR 7 Absent Nil 45 15

24/m +0.25 (0.0) +0.25 (0.0) ET 55 55 BMR 6 P 100 5 5

25/m Plano (0.0) Plano (0.0) ET 90 60 BMR 7 Absent Nil 35 5

28/m Plano (0.0) Plano (0.0) ET 45 45 PD BLRx†† 9 Absent Nil 0 0

20/m +1.0+2.0×180 (0.3)

+1.0+2.0×110 (0.3)

ET 30 30 PD BLRx 7 Absent Nil 5 5

17/f +0.50 (0.18) +0.50 (0.18) XT 40 40 BMRx‡‡ 6 P 240 0 025/m Plano (0.0) Plano (0.0) ET 35 35 BLRx 8 Absent Nil 0 0

*BCVA: Best corrected visual acuity in Log MAR in brackets after appropriate correction, †PD: Strabismus measured in prism diopters, ‡BMR: Bimedial recession, **BLR: Bilateral recession, ††BLRx: Bilateral resection, ‡‡BMRx: Bimedial resection

Table 2: Median inflammatory scores and P value during post‑operative follow‑up

Redness Congestion Foreign body sensation

Chemosis Drop intolerance

Total inflammatory 

score

MISS SPSS MISS SPSS MISS SPSS MISS SPSS MISS SPSS MISS SPSS

First post op day

Median 3 3 3 3 1 2 0 1 1 1 6.5 10

P value 0.65 0.65 0.01 0.08 0.08 0.04

Two‑three weeks

Median 1 2 1 2 0 1.5 0 0 0 0 2 5.5

P value 0.03 0.03 0.02 1.00 0.31 0.04

Six weeks

Median 0 1 0 1 0 0 0 0 0 0 0 2P value 0.04 0.06 0.317 1.00 1.00 0.05

MISS: Minimally invasive strabismus surgery, SPSS: Standard paralimbal strabismus surgery

a limbal approach in cases undergoing horizontal rectii surgeries.[6] Although his main outcome measures (fusion, alignment, and vision) were different  from ours, Mojon did report significantly less lid swelling (0% vs. 21%) in the MISS group on  the first  post‑operative day. On final  analysis  at 6 months,  no  significant difference was  found.  In  another study on exotropes, Pellanda and Mojon compared the MISS approach with a historical group.[7] They found significantly less conjunctival swelling and injection on the first post‑operative day (χ2 test P < 0.001). They needed to convert 3/104 muscles in their MISS group.[7]

In a similar analysis in esotropia, conjunctival swelling and injection were significantly less pronounced (χ2 P value < 0.001) in the MISS group.[8] We believe that a comparison of grades of inflammation by the Mann‑Whitney test would have been superior, although the results are unlikely to have been different.

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our readers. As is evident, 11 of 14 surgeries achieved correction to within 10 PD of target angle; a success rate of 78.5%.

As highlighted by Kushner, the MISS approach interferes less with the peri‑limbal episcleral vessels, which should decrease the chances of anterior segment ischemia.[9] Although MISS may appear to be superior to the paralimbal approach, it may not be much different to the Parks fornix approach where too conjunctival incisions are far removed from the limbus.

We are acutely aware of the small number of cases in our study and suggest that more studies with a larger sample size would yield better evidence  to either  support or  refute our findings.  Since  all  our patients were young adults,  the results should be interpreted preferable for this age group. The strength of our study is in its parallel design, a format superior in our opinion to compare inflammation scores.

ConclusionOur small study shows that a MISS approach is more comfortable and offers better cosmesis (in terms of redness) in the short‑term (2‑3 weeks) as compared to the SPSS; this difference  equates by  4‑6 weeks.  It  offers  an  attractive alternative conjunctival approach to strabismus surgery.

References1. Darzi A, Mackay S. Recent advances in minimal access surgery.

BMJ 2002;324:31‑4.2. Harms H. Uber Muskelvorlagerung. Klin Monatsbl Augenheilk

1949;115:319‑24.3. Parks MM. Fornix incision for horizontal rectus muscle surgery.

Am J Ophthalmol 1968;65:907‑15.4. Velez G. Radial incision for surgery of horizontal rectus muscles.

J Pediatr Ophthalmol Strabismus 1980;17:106‑7.5. Swan KC, Talbott T. Recession under Tenon’s capsule. Arch

Ophthalmol 1954;51:32‑41.6. Mojon DS. Comparision of a new, minimally invasive strabismus

surgery technique with the usual limbal approach for rectus muscle recession and plication. Br J Ophthalmol 2007;91:76‑82.

7. Pellanda N, Mojon DS. Combined horizontal rectus muscle minimally invasive strabismus surgery for exotropia. Can J Ophthalmol 2010;45:363‑7.

8. Pellanda N, Mojon DS. Minimally invasive strabismus surgery in horizontal rectus muscle surgery for esotropia. Ophthalmologica 2010;224:67‑71.

9. Kushner BJ. Comparision of a new minimally invasive strabismus surgery technique with usual limbal approach for rectus muscle recession and plication. Br J Ophthalmol 2007;91:5.

Figure 2: Comparative photograph at 2‑3 weeks postoperatively, of the same patient operated through MISS and SPSS

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