Efficacy of modified Park’s technique in the treatment of children with strabismus

Purpose: To investigate the efficacy of modified Park’s technique in children with strabismus. Methods: A total of 120 patients were recruited in the Department of Ophthalmology, Anhui Provincial Children's Hospital, Anhui, China between January 2019 and December 2021. The patients were divided into study and control groups comprising 60 patients each. Control group underwent rectus muscle adjustment suture using standard incision, while study group received modified Park’s technique, which involved intermuscular membrane incision and conjunctiva two-layer suture method. Various parameters such as perioperative indicators, tear film function, and patient satisfaction were assessed. Results: The study group had significantly lower intraoperative blood loss, duration of surgery and length of hospital stay (p < 0.01). Also, it showed significantly higher Schirmer’s time, tear film break-up time (TFBUT) time and significantly lower corneal staining score (p < 0.01). Satisfaction level was significantly higher in the study group compared to control group (p < 0.05). So also was clinical efficacy (91.67 %) compared to control group (83.33 %). Furthermore, study group exhibited significantly lower incidence of complications (5) compared to control group (11; p < 0.05). Conclusion: Enhanced Park’s technique improves perioperative indicators, tear film function, and satisfaction level; it also produces high efficacy and lower incidence of complications. This suggests that it might be a viable substitute for conventional treatment of children with exotropia. However, long-term follow-up data will be required to establish the superiority of this treatment strategy.

In traditional Chinese medicine (TCM), strabismus in children is classified as ophthalmoplegia or visual divergence, often attributed to blocked meridians caused by wind, phlegm, and stasis.This obstructs the flow of qi and blood while depriving tendons and muscles of nourishment and relaxation, resulting in oblique eyes.Intermittent external strabismus is mostly associated with qi deficiency, resulting from lack of positive qi, weakened external guard consolidation, and deficiency in veins and ligaments.Hence, this study incorporates the use of Buzhong Yiqi decoction as a treatment approach.This study investigated the efficacy of modified Park's technique in the treatment of strabismus in children.

General patient data
This research was conducted at Anhui Provincial Children's Hospital in Hefei, Anhui Province, China, comprising 120 children diagnosed with strabismus.Patients were randomly assigned using an online web-based tool (http://www.randomizer.org/)to two groups namely; study and control groups.An independent research assistant, not involved in participant screening or evaluation, managed the randomization process.The original calculation for sample size determined that 60 patients in each group would be sufficient to detect a 3-point difference between two groups in a two-sided significance test, with a statistical power of 0.8 and an alpha error level of 0.05.
All patients and their guardians received comprehensive information and provided informed consent by signing respective documentation before participating in the study which adhered to the ethical standards outlined in the Declaration of Helsinki [8].The study received approval from the Ethics Committee of Anhui Provincial Children's Hospital, China (approval no.CHA18239474).

Inclusion criterion
Patients who met diagnostic criteria for strabismus as specified in the 9 th edition of ophthalmology [9].

Exclusion criteria
Patients with abnormal eye movements or A-V signs, nystagmus, vertical strabismus, a history of eye surgery or trauma, or any other ocular diseases, surgical intolerance, abnormal immune function, refractive interstitial opacity, or neurological diseases were excluded from this study.

Interventions
Patients were in the supine position and received general anesthesia.In preparation for surgery, the conjunctival sac was rinsed with 0.3 % povidone-iodine.Compound epinephrine was applied to the conjunctival surface to constrict capillaries and minimize intraoperative blood loss.
For medial rectus surgery, an arcuate incision was made 5 mm away from the cornea in the nasal region.For lateral rectus surgery, an arcuate incision was made 7 mm away from the cornea in the temporal region.The bulbar conjunctiva was cut open, and the rectus muscle was secured in place using a strabismus hook.Thereafter, bulbar conjunctiva and fascia were dissected to fully expose the rectus muscle.A double-loop suture was performed using a 6 -0 absorbable suture, approximately 2 mm from the endpoint of rectus muscle.The medial or lateral rectus muscle was then cut about 1 mm posterior to its end to allow for recession.Suture was advanced obliquely at the posterior edge of the insertion point of rectus muscle, emerging from the anterior edge.Needle was passed through the superficial sclera at the end of the rectus muscle.Configuration of the suture resembled a "V", with its tip facing the cornea, and the amount of muscle recession was measured.The suture was tightened without ligating according to the preoperative suspension muscle design.The conjunctiva was secured with a silk thread.Following operation, tobramycin and dexamethasone ophthalmic ointment were applied to the conjunctival sac.If necessary, the suture was adjusted 1-2 days after surgery based on eye position.
In control group, rectus muscle adjustment suture was performed using the conventional incision method.A 5 -10 mm bulbar conjunctival fornix incision was made, and the medial or lateral rectus muscle was secured using a strabismus hook.Intermuscular membrane and ligamentum temperatum were dissected.After performing a double-loop suture using 6 -0 absorbable sutures, extraocular muscles were shortened according to preoperative design, and conjunctival incision was sutured.
Both groups of patients received oral dexamethasone tablets (5 mg/day) for three consecutive days.Levofloxacin and praprofen eye drops were administered four times daily for two consecutive weeks.
Additionally, both groups received treatment with Buzhong Yiqi decoction, which included 12 g each of Codonopsis radix and Astragali radix, 9 g each of Atractylodis macrocephalae rhizoma, Rehmanniae radix, Angelicae sinensis radix, Bupleuri radix, Scrophulariae radix, and Cimicifugae rhizoma, and 6g each of tangerine peel, Ophiopogonis radix, and liquorice root.The herbs were decocted with water and administered every other day for six months.

Postoperative indicators
Amount of blood loss during surgery, duration of surgical procedure, and length of hospital stay was recorded.

Efficacy
Efficacy was classified as cured (following treatment, symptoms vanished, and eye position was restored, with degree of strabismus decreasing to less than 5 △ ), effective (a noticeable improvement in symptoms, and degree of strabismus dropped to between 5 △ and 10 △ after treatment), and ineffective (despite treatment, there was no significant improvement in symptoms) [10].

Tear film function
Schirmer's test procedure involved placing a sterile test paper below the patient's eye in the conjunctival sac.Patient was instructed to look straight ahead for a few seconds and then keep their eyes closed.After 5 mins, the paper strip was collected, and the length of moistened area was measured.In the tear film break-up time (TFBUT) test, sodium fluorescein was applied to the conjunctival surface, and eye was examined using a slit lamp.Lamp was switched to a cobalt blue filter, and patient was instructed to blink once and keep their eyes open.A dark spot indicating a dry area appeared after the patient blinked.Tear film break-up time (TFBUT) was calculated as the time interval between the last blink and appearance of the first dark spot.For corneal fluorescein staining score, a solution of sodium fluorescein was placed on patient's cornea, and eye was observed under cobalt blue light to determine staining pattern.Cornea was divided into quadrants, and each quadrant was assigned a score from 0 to 3. Total score across all quadrants ranges from 0 to 12 with lower scores indicating better tear film function.

Satisfaction with surgery
After a 28-day post-surgery period, a survey was administered to evaluate patient satisfaction.The survey included questions regarding the efficacy of surgery and any discomfort experienced.Each question was assigned a score of 1 to 5. A score of 80 -100 indicated a very high level of satisfaction, 60 -80 indicated satisfaction while < 60 indicated dissatisfaction.

Complications
Occurrences of complications, which included conjunctivitis, corneal edema, diplopia and scar adhesion were recorded.

Statistical analysis
Data processing was conducted using Statistical Packages for Social Sciences (SPSS 23.0).Enumeration data were presented as N (%) and analyzed using Chi-square test.Normally distributed measurement data were represented as mean ± standard deviation (SD).Comparison of means between two groups was carried out using chi-square F-test.Data showing chi-square differences were tested using independent samples t-test, while data with non-chi-square differences were analyzed using independent samples t-test.Intra-group pre-and postcomparisons were performed using paired samples t-test.P < 0.05 was considered statistically significant.

Patient data
There was no statistical difference in clinical data between study and control groups (p > 0.05; Table 1).

Perioperative indicators
Perioperative indices in study group showed significant improvement compared to control group.(p < 0.05; Table 2).

Tear film function
Following intervention, the use of modified Park's technique led to significantly improved tear film function, when compared to rectus muscle adjustment suture.
Data was significantly reduced in both groups after intervention, and tear film function was significantly better in study group compared to control group (p < 0.05; Table 3).

Satisfaction level
Satisfaction level in study group was significantly higher compared to control group (p < 0.05; Table 4).

Clinical efficacy
Patients in study group exhibited higher treatment efficacy rate compared to control group (p < 0.05) (Table 5).

Incidence of complications
Study group had lower incidence rate of complications compared to control group (p < 0.05) (Table 6).

DISCUSSION
Strabismus is commonly associated with craniocerebral injury and neurological diseases [11,12].It typically manifests before age 5, causing alignment issues and vision loss as children struggle to align their eyes correctly [13].
Vision training, along with appropriate eye surgery, aids in the recovery of eyesight, with corrective surgery being the primary management method for strabismus in current practice [13][14][15].
For children with external strabismus, the root cause often lies in an internal deficiency of middle-qi and lack of glory of Ying and blood.This leads to deficiency of yin and blood and excessive yang activity, resulting in intermittent and sudden eye strabismus.Main clinical symptoms include qi deficiency, with strabismus occurring after physical exhaustion or loss of mental focus.Buzhong Yiqi decoction, containing Astragali radix benefits qi, Codonopsis radix and Atractylodis macrocephalae rhizoma strengthen and nourishes spleen and middle-qi, tangerine Peel regulates qi, Angelicae sinensis radix tonifies blood, Cimicifugae rhizoma and Bupleuri radix elevate and strengthens middle-qi, Ophiopogonis radix nourishes Yin and blood, are used as a combination treatment option.
The modified technique of Park's incision, combined with two layers of intermuscular and conjunctival sutures, contributes to the restoration of tertiary visual function in both eyes of children with external strabismus.It also promotes the attainment of functional eye position after surgery.
Compared to control group, study group showed lower perioperative scores, which is attributed to accurate lesion localization and smaller conjunctival incision using modified Park's technique.These factors significantly reduced intraoperative bleeding, operative time, and postoperative complications.The less invasive nature accelerated healing, shortened hospital stays reduced pain and treatment costs.Additionally, study group exhibited improved tear film function when compared to control group.Thus, modified Park's technique was less damaging to aqueous and mucus layers of tear film.Furthermore, this procedure minimizes conjunctival scarring, nerve damage and irritation in postoperative period, leading to enhanced tear film stability and recovery [16][17][18].
Study group surpassed control group in terms of treatment efficacy, complication rate and satisfaction with surgery primarily due to smaller conjunctival incision and reduced postoperative pain.Park's technique, originally developed by Dr Marshall Parks, an American ophthalmologist in 1968, eliminates the need for tissue dissection anterior to muscle insertion, thereby reducing nerve damage.This may be considered as a therapeutic option in future.

Limitations of this study
This current study has some limitations.Firstly, the sample size used was relatively small, which may limit the generalizability of findings.Secondly, lack of long-term follow-up data did not establish durability of treatment outcomes over an extended period.

CONCLUSION
Modified Park's technique is highly efficacious for the treatment of strabismus in children.This technique minimizes surgical wounds and reduces the length of surgical procedures and hospital stays.As a result, patients undergoing this technique experience a lower incidence of complications and a higher level of satisfaction.Thus, modified Park's technique may be considered a preferred surgical option for treating strabismus in children following collection of long-term follow-up data to establish durability of treatment in the future.

DECLARATIONS
2023 The authors.This work is licensed under the Creative Commons Attribution 4.0 International License reducing postoperative complications have become key priorities in clinical practice.

Table 3 :
Comparison of tear film function (mean ± SD, N = 60 in each group)

Table 4 :
Comparison of satisfaction (N = 60 in each group)

Table 5 :
Efficacy of treatment (N = 60 in each group)