The study design was a cross-sectional descriptive analysis. Fifty-seven patients diagnosed with ACD who attended the Ophthalmology Outpatient Clinic, Thammasat Hospital, Pathum thani, between August 2022 and September 2023 were included in the present study. The diagnoses of allergic conjunctivitis and clinical severity were made by a cornea specialist. This study was conducted with the approval of the Medical Ethics Committee of Thammasat University (MTU-EC-OP-1-122/65) from 8 August 2022 to 7 August 2023 in accordance with the tenets of the Declaration of Helsinki. Prior to participating in the study, the parents or guardians of all patients provided written informed consent.

The diagnosis of ACD was established based on clinical symptoms including itching, redness, photophobia, foreign body sensation, or increased mucous discharge, along with observable signs including conjunctival hyperemia, chemosis, tarsal conjunctival papillary reaction, or Horner-Trantas dots. SAC is defined as bilateral acute ACD that occurs seasonally. Since Thailand only has summer, rainy, and winter seasons, the spring and autumn seasons do not apply. PAC is defined as bilateral chronic, self-limiting ACD that can occur throughout the year. VKC is defined as bilateral chronic ACD that leads to a papillary response, mainly in the limbus or upper tarsus. AKC is defined as bilateral chronic ACD accompanied by dermatitis [8].

Patients aged between 5 to 18 years old were included in the study. Exclusion criteria encompassed: (1) patients with ocular media opacity that affected the cornea, lens, or vitreous humor, hindering ocular surface and refractive measurements, (2) patients diagnosed with amblyopia due to causes other than refractive error, (3) patients allergic to cyclopentolate, and (4) patients previously treated for allergies with controlled symptoms, defined as exacerbations occurring ≤ 4 days per week or < 4 weeks. A single examiner conducted a comprehensive ocular examination and clinical assessment of all participants.

The study collected demographic information comprising age, gender, underlying medical conditions, history of drug allergies, family history of allergies, exposure to pets, and a comprehensive history of ocular and systemic allergies. Subsequently, all patients underwent a complete ocular examination by slit-lamp biomicroscopy. A questionnaire was employed to evaluate the severity of ocular symptoms and signs. Symptoms including itching, tearing, photophobia, foreign body sensation, and irritation, as well as signs including eyelid swelling, lid margin inflammation, conjunctival injection and edema, eye discharge, tarsal conjunctival reaction, limbal involvement (such as Horner-Trantas dots), and corneal involvement (such as punctate epithelial erosion and Shield ulcer), were graded for severity on a scale ranging from 0 (indicating absence) to 4 (indicating seriousness). The evaluations were performed by a single clinician. The summation of the total scores obtained from these evaluations was represented as the Ocular Allergy Severity Score (OCAS Score) for symptoms and signs.

The initial visual acuity (Snellen chart) was assessed. Subsequently, cycloplegic refraction was conducted using 1% Cyclopentolate hydrochloride eyedrops [Batch No. N23G04, Mfg. Date 07/2023 Exp. Date 06/2025], administered as 1 drop every 5 minutes for 2 applications, followed by a 30-minute waiting period before performing retinoscopy. The Best Corrected Visual Acuity (BCVA) was determined during the second visit, wherein the participants were fitted with glasses based on the results obtained from the cycloplegic refraction assessment.

A diagnosis of refractive amblyopia was established based on a reduction in BCVA worse than 20/30 OU for bilateral amblyopia or an interocular difference of two or more lines, with the better eye maintaining normal visual acuity in unilateral amblyopia [9]. Amblyogenic refractive errors, which are severe refractive errors more likely to result in refractive amblyopia, were identified by the presence of 1.0–1.5 diopters (D) or more of hyperopia, 2.0 D or more of astigmatism, and 3.0–4.0 D or more of myopia in cases of anisometropic refractive error. In isoametropic refractive errors, involves the presence of 5.0–6.0 D or more of myopia, 4.0–5.0 D or more of hyperopia, or 2.0–3.0 D or more of astigmatism [10].

The OCAS Score was determined with modifications based on two previous studies [7, 11]. The severity of ACD symptoms was assessed based on a history of five symptoms: itchy eyes, watery eyes, light sensitivity, eye irritation, and eye pain. Each symptom was graded on a scale from 0 to 4 as follows: grade 0 = no symptoms, grade 1 = mild symptoms, grade 2 = symptoms present for half of the day, grade 3 = symptoms experienced for most of the day, and grade 4 = symptoms experienced throughout the entire day. The severity of ACD signs was assessed based on six signs: eyelid position, including eyelid skin texture and eyelid margin; conjunctival redness and edema; eyelid and tarsal conjunctiva inflammation; limbal involvement; and corneal involvement. Each sign was graded on a scale from 0 to 4, following the criteria established in the previous study [11].

The corneal tomographic parameters, including CCT at the corneal apex, Km, KISA% index, and BAD-D, were measured using Pentacam (Oculus, Inc.) version 1.27r11. The corneal biomechanical parameters, such as IOP, CCT, CBI, and TBI, were measured using Corvis ST (Oculus, Inc.) version 1.6r2223.

The sample size was calculated based on Taro Yamane's sample size formula. The statistical analyses were conducted utilizing SPSS software version 23.0 (SPSS, Inc.). Clinical characteristics and outcome data are reported as percentages and mean values with standard deviation. Group means were compared through the use of an independent t-test and Mann-Whitney U-test. The threshold for statistical significance was established at p < 0.05 for all the tests performed.