Abstract
Objectives
To evaluate the effects of short-acting cycloplegic agents, tropicamide and compound tropicamide, on ocular biological parameters and choroid thickness.
Methods
In this study, seventy pediatric subjects aged 6 to 13 years were randomly assigned to two groups: the tropicamide group and compound tropicamide group. Ocular biological parameters and choroidal thickness (CT) and subfoveal choroid thickness (SFCT) were measured in both groups and were retested 40 min after drug administration. The tropicamide eye drops were administered into the conjunctival sac every 5 min with 1 drop, for a total of 4 doses. Compound tropicamide was administered in the same way as tropicamide. Ocular biological parameters included refraction (spherical equivalent, SE), intraocular pressure (IOP), axial length (AL), anterior chamber depth (ACD), lens thickness (LT), central corneal thickness (CCT), and white to white (WTW). The CT is the regional inferior choroidal thickness of nine sectors centered on the macular fovea and automatically generated using an ETDRS grid. And the SFCT is the choroidal thickness at the subfoveal point of the macular region.
Results
After application of tropicamide and compound tropicamide to induce the ciliary muscle paralysis, SE, AL, and LT decreased, while ACD, CCT, and WTW increased compared to baseline(all P values < 0.05). There was no significant change in IOP before and after cycloplegia (p > 0.05). The CT in the nasal quadrant before and after ciliary paralysis was significantly thinner than other areas, the CT in the temporal quadrant was significantly thicker than others, and the CT in the inner quadrant was higher than the CT in the outer quadrant. In the tropicamide group: CT was significantly increased in the remaining quadrants except the inner inferior(I) and outer superior(S) quadrants (p < 0.05), and SFCT was also significantly increased (p = 0.005). In the compound tropicamide group: there is a significant increase in CT outer superior(S) quadrant CT (p = 0.043). Increase in the mean values of CT and SFCT in the remaining quadrants was also observed, but the difference was not statistically significant (p > 0.05). Additionally, AL and SFCT were negatively correlated.
Conclusions
Some ocular biological parameters were altered after application of short-acting cycloplegic agent tropicamide and compound tropicamide to paralyze the ciliary muscle. Compared with compound tropicamide, tropicamide eye drops can reduce axial length while increasing choroid thickness.
Keywords: Tropicamide, Compound tropicamide, Children, Ocular biological parameters, Choroid thickness
Introduction
Myopia is a significant global public health issue, projected to affect 49.8% of the world’s population by 2050, with approximately 20% developing high myopia [1]. With the use of electronic devices, the incidence of myopia is on the rise, especially in the child and adolescent population. A 2021 study [2] found that the prevalence of myopia among 34,644 students in Shenyang City, Liaoning Province, China, was 60%. Of these, 45% had mild myopia, 13% had moderate myopia, and 1.9% had severe myopia. Sharon Y L Chua et al. [3] followed up with 928 schoolchildren aged 7–9 years in the Singapore Cohort of Risk Factors for Myopia (SCORM) for up to 11 years, it was found that the younger the age of onset of myopia or the longer the duration of myopic progression in myopic children, the more likely they were to progress to high myopia.
Currently, there is no definitive cure for myopia, highlighting the importance of early prevention to control its progression. Clinically effective interventions for myopia prevention and control include defocus framework glasses, orthokeratology lens, and 0.01% atropine sulfate eye drops. Atropine is a typical M cholinergic receptor blocker, it paralyzes the ciliary muscle, leading to relaxed accommodation. Additionally, atropine may stimulate the release of dopamine and nitric oxide [4], promoting scleral remodeling and increasing choroid thickness [5]. Low-concentration of atropine, the most commonly used in clinical practice, significantly reduces side effects; however some children still experience photophobia [6]. The choroid [7] is a highly vascularized tissue situated between the sclera and Bruch’s membrane. It has one of the highest blood flows per unit weight of any human tissue and provides essential nutrition to the outer layer of the retina. As the possible mechanisms of myopia have been intensively investigated, there has been an increasing number of studies related to the choroid. SS-OCTA [8] is a new, non-invasive imaging technique that quickly generates volumetric angiography images. It offers high resolution and three-dimensional imaging, making it ideal for early monitoring of retinal choroidal blood flow and thickness changes in children. Research shows that the CT of the macular region is thickest in hyperopia, second in emmetropia, and thinnest in myopia. Additionally, CT positively correlates with the number of refractive errors in myopic patients [9, 10], and that the thinning of the CT in myopic eyes is associated with the onset and progression of myopia.
Tropicamide and compound tropicamide have anticholinergic effects similar to those of atropine and are short-acting cycloplegic agent. They restore normal eye accommodation about 6 h after discontinuation the drug, with fewer adverse effects, making them easy for both children and parents to accept and are associated with fewer adverse effects, making them more acceptable to both children and parents. This study administered tropicamide and compound tropicamide eye drops continuously over a short period. We compared changes in ocular biological parameters and choroid thickness in children before and after cycloplegia to investigate how short-acting cycloplegic agents affect these parameters. This research aims to identify effective treatments for myopia and provide data to support its prevention and control in children and adolescents.
Materials and methods
Study population
This study conformed to the guidelines of the Declaration of Helsinki. All participants in the study were entirely voluntary. Informed consent was signed by all enrolled subjects and their parents or legal guardians before ophthalmologic examination and all procedures of the study followed the ethical principles of human being and the institutional review board of our university approved the study.
Subjects were recruited from children aged 6 to 13 years who visited the Department of Ophthalmology at the First Affiliated Hospital of Bengbu Medical University between November 2023 and June 2024. They were randomly assigned to tropicamide and compound tropicamide groups. Inclusion criteria included a best corrected visual acuity (BCVA) of ≥ 0.8, normal intraocular pressure (IOP) between 10 and 21 mmHg, clear refractive media, the range of diopter degree was + 0.5D ~ -2.5D, astigmatism of no more than 1.50 D, and an OCTA image signal of ≥ 9. Exclusion criteria included the use of medications with vascular effects, wearing orthokeratology lenses, using atropine drops within the past month, and having a history of ocular trauma, strabismus surgery, or other ocular diseases. Both eyes of all subjects were included in the study, and one eye was enrolled when there was a large difference in fundus system error in one eye. The drug administration was standardized, the drug was administered by a specialized ophthalmology professional, and the patient was instructed to close his eyes and rest after dripping.
Drugs and instruments
Tropicamide Eye Drops (Shandong Bausch Lomb Forida Pharmaceutical Co., China; Drug Code, H20023088) 6 ml, Main component: tropicamide 30 mg.
Compound Tropicamide Eye Drops (Shenyang Xingqi Ophthalmic Pharmaceuticals Co., China; Drug Code, H20055546) 5 ml, Main components: tropicamide 25 mg and phenylephrine hydrochloride 25 mg.
Computerized Optometry (Topocon, Japan).
Non-Contact Tonometer (TOMEY, Japan).
Ocular Biometry IOLmaster-700 (ZEISS, Germany).
Swept-source Optical Coherence Tomography Angiography SS-OCTA (Tupai, Beijing).
Research methodology and observation indicators
All subjects first underwent a comprehensive ophthalmologic examination that assessed several parameters: refractive error (spherical equivalent, SE), intraocular pressure (IOP), axial length (AL), anterior chamber depth (ACD), lens thickness (LT), central corneal thickness (CCT), white-to-white (WTW) distance, and fundus choroidal thickness. Refraction was represented as spherical equivalent (SE), calculated as the spherical value plus half of the cylindrical value. AL is the distance from the anterior surface of the cornea to the retinal pigment epithelium. After the examination, cycloplegia was randomly performed using either tropicamide eye drops or a compound of tropicamide eye drops. Used by a professional ophthalmic professional, dosed every 5 min, into the conjunctival sac for a total of 4 times, and the patient was instructed to rest with their eyes closed after a drip. The eyes were closed for 40 min after the last eye drop application, and the above measurements were repeated again. Measurements were performed between 09:00 and 11:00 on the same day to minimize the effect of daily variations in ocular parameters [11].
Choroidal thickness in the fundus was measured using the SS-OCTA. This involved automatically layering the ETDRS grid with an 18 × 18 mm scanning pattern centered on the central concavity of the macula. The grid was centered on the macular central concavity and automatically generated three concentric circles with inner, middle, and outer diameters of 1, 3, and 6 mm, respectively, and was further subdivided into four quadrants of temporal(T), superior(S), nasal(N) and inferior(I), with a total of nine sectors (Fig. 1A). Choroid Thickness (CT), which is the thickness between Bruch’s membrane and the choroidal-scleral interface, was localized in the central concavity of the Choroid Thickness, and the average regional thickness of each grid was automatically calculated by the system and manually corrected (Fig. 1B). Subfoveal choroid thickness (SFCT), a perpendicular line was drawn toward the choroid at the most concave point of the central macular depression, and the choroid thickness was determined on this line (Fig. 1C).
Fig. 1.
Illustrates the choroid thickness in the macular area. (A): Shows the ETDRS grid, which displays the choroid thickness (CT) for each sector of the macula. The letters T, S, N, and I represent the temporal, superior, nasal, and inferior sectors, respectively. (B): The system automatically generates CT values for each sector of the ETDRS grid shown in a. (C): The green segment between the green horizontal line shows the subfoveal choroidal thickness in the macular region
Statistical analysis
Statistical analysis was conducted using SPSS version 27. Demographic characteristics were analyzed using the chi-square test, and gender was reported as a percentage. To assess normality, a normality test was conducted. If the data were normally distributed, a paired t-test was performed; otherwise, a nonparametric test was used. Using the Pearson correlation analysis, the correlation coefficient of AL and SFCT was the r value. Results are presented as mean values with standard deviations. For all the tests, P < 0.05 was considered significant.
Results
Basic information
The study recruited a total of 70 children aged 6 to 13 years. The tropicamide group included 40 participants with a total of 79 eyes, comprising 48 males and 31 females, with a mean age of 8.40 ± 1.68 years. The compound tropicamide group included 30 participants with a total of 59 eyes, comprising 26 males and 33 females, with a mean age of 9.40 ± 1.73 years. No statistically significant differences in age and gender were observed between the two groups (P > 0.05) (Table 1).
Table 1.
Basic information of participants in both groups
| Normative | Tropicamide group(n = 79) | Compound tropicamide group(n = 59) | χ2 | P | |
|---|---|---|---|---|---|
| Age/years | 8.40 ± 1.68 | 9.40 ± 1.73 | 1.194 | 0.232 | |
| Sex/instance(%) | Male | 48(60.8%) | 26(44.1%) | 3.784 | 0.052 |
| Femal | 48(60.8%) | 33(55.9%) | |||
Changes in biological parameters of the eye
Following the administration of tropicamide to paralyze the ciliary muscle, the degree of myopia was reduced, SE drifted toward hyperopia, AL shortened, ACD deepened, LT decreased, and CCT and WTW increased (all P values < 0.05)(Table 2). The ocular biological parameters exhibited identical alterations tendency following the administration of compound tropicamide to paralyze the ciliary muscle(Table 3).
Table 2.
Comparative analysis of ocular biological parameters before and after cycloplegia induced by tropicamide
| Cycloplegia before | Cycloplegia after | P | |
|---|---|---|---|
| SE(D) | -1.11 ± 0.97 | -0.98 ± 0.94 | 0.027 |
| IOP(mmHg) | 15.60 ± 2.61 | 15.49 ± 2.61 | 0.396 |
| AL(mm) | 24.1089 ± 1.1295 | 24.1016 ± 1.1297 | 0.001 |
| ACD(mm) | 3.66 ± 0.24 | 3.74 ± 0.24 | < 0.001 |
| LT(mm) | 3.36 ± 0.14 | 3.33 ± 0.12 | < 0.001 |
| CCD(um) | 537.81 ± 31.31 | 541.54 ± 30.76 | < 0.001 |
| WTW(mm) | 12.19 ± 0.47 | 12.28 ± 0.55 | < 0.001 |
Mean ± SD, SE = spherical equivalent, IOP = intraocular pressure, AL = axial length, ACD = anterior chamber depth, LT = lens thickness, CCT = central corneal thickness, WTW = white-to-white
Table 3.
Comparative analysis of ocular biological parameters before and after cycloplegia induced by compound tropicamide
| Cycloplegia before | Cycloplegia after | P | |
|---|---|---|---|
| SE(D) | -1.15 ± 0.95 | -0.83 ± 1.10 | < 0.001 |
| IOP(mmHg) | 16.63 ± 2.90 | 16.93 ± 3.13 | 0.521 |
| AL(mm) | 24.1678 ± 1.1271 | 24.1620 ± 1.2142 | 0.020 |
| ACD(mm) | 3.63 ± 0.15 | 3.72 ± 0.25 | < 0.001 |
| LT(mm) | 3.37 ± 0.14 | 3.32 ± 0.12 | < 0.001 |
| CCD(um) | 525.83 ± 33.89 | 533.89 ± 35.27 | < 0.001 |
| WTW(mm) | 12.10 ± 0.33 | 12.37 ± 0.42 | < 0.001 |
Mean ± SD, SE = spherical equivalent, IOP = intraocular pressure, AL = axial length, ACD = anterior chamber depth, LT = lens thickness, CCT = central corneal thickness, WTW = white-to-white
Changes in choroid thickness
CT in both anterior and posterior nasal quadrants of the ciliary muscle paralyzed by application of tropicamide and compound tropicamide were significantly thinner than the other regions. Conversely, CT in the temporal quadrant was significantly thicker than in other areas, and CT in the inner circle quadrant was greater than that in the outer circle quadrant(Fig. 2).
Fig. 2.
Choroid Thickness under the macular area in each sector, T, S, N, and I correspond to the temporal, superior, nasal, and inferior sectors of the ETDRS grid, using Figure A as an example. (A): Shows CT before cycloplegia in the tropicamide group. (B): Shows CT after cycloplegia in the tropicamide group. (C): Shows CT before cycloplegia in the compound tropicamide group. (D): Shows CT after cycloplegia in the compound tropicamide group
In the tropicamide group, significant increases in choroid thickness (CT) were noted in all quadrants except the inner I and outer S quadrants (p < 0.05), along with a significant increase in subfoveal choroid thickness (SFCT) (p = 0.005)(Table 4). In the compound tropicamide group, significant increase in the outer S quadrant CT (p = 0.043), mean value of CT in the remaining quadrants increased, but there was no statistically significant difference; mean value of SFCT increased, and the difference was also not statistically significant (p > 0.05)(Table 5).
Table 4.
Comparative analysis of choroid thickness before and after cycloplegia induced by tropicamide
| Cycloplegia before(μm) | Cycloplegia after(μm) | P | |
|---|---|---|---|
| Central ring(1 mm in diameter) | 257.76 ± 65.96 | 266.58 ± 66.74 | 0.007 |
| Inner ring(3 mm in diameter) | |||
| TCT | 275.00 ± 56.66 | 281.65 ± 58.40 | 0.042 |
| SCT | 256.18 ± 60.81 | 261.75 ± 61.95 | 0.041 |
| NCT | 211.82 ± 65.94 | 230.90 ± 66.82 | 0.013 |
| ICT | 257.75 ± 63.01 | 264.35 ± 67.12 | 0.113 |
| Outer ring(6 mm in diameter) | |||
| TCT | 272.56 ± 49.71 | 278.57 ± 52.27 | 0.043 |
| SCT | 249.91 ± 56.05 | 253.73 ± 56.98 | 0.150 |
| NCT | 176.05 ± 57.71 | 183.75 ± 62.27 | 0.047 |
| ICT | 239.92 ± 57.00 | 248.19 ± 64.90 | 0.048 |
| SFCT | 257.10 ± 67.30 | 266.13 ± 67.50 | 0.005 |
Mean ± SD, T = temporal, S = superior, N = nasal, I = inferior, CT = choroidal thickness, SFCT = subfoveal choroid thickness
Table 5.
Comparative analysis of choroid thickness before and after cycloplegia induced by compound tropicamide
| Cycloplegia before(μm) | Cycloplegia after(μm) | P | |
|---|---|---|---|
| Central ring(1 mm in diameter) | 261.34 ± 54.03 | 262.58 ± 57.71 | 0.444 |
| Inner ring(3 mm in diameter) | |||
| TCT | 277.32 ± 52.18 | 279.32 ± 54.87 | 0.228 |
| SCT | 257.66 ± 52.48 | 260.51 ± 56.41 | 0.107 |
| NCT | 224.03 ± 53.77 | 225.97 ± 56.51 | 0.181 |
| ICT | 257.78 ± 52.26 | 259.75 ± 53.84 | 0.225 |
| Outer ring(6 mm in diameter) | |||
| TCT | 277.47 ± 52.61 | 279.66 ± 54.42 | 0.225 |
| SCT | 251.00 ± 53.32 | 254.76 ± 54.75 | 0.043 |
| NCT | 176.61 ± 47.66 | 178.63 ± 49.79 | 0.168 |
| ICT | 245.15 ± 50.44 | 246.17 ± 54.78 | 0.462 |
| SFCT | 260.98 ± 55.01 | 262.24 ± 58.90 | 0.428 |
Mean ± SD, T = temporal, S = superior, N = nasal, I = inferior, CT = choroidal thickness, SFCT = subfoveal choroid thickness
Correlation of AL and SFCT
AL and SFCT before and after cycloplegia were negatively associated in both groups. Additionally, a weak correlation was noted between the changes in AL and the changes in SFCT after administering tropicamide in the tropicamide group. Although the correlation was weaker, it was statistically significant(r=-0.341, P = 0.004). In contrast, no correlation was found between the changes in AL and the changes in SFCT following the administration of compound tropicamide (r=-0.190, P = 0.154))(Table 6).
Table 6.
Correlation analysis of AL and SFCT
| r-value(Cycloplegia before) | r-value(Cycloplegia after) | r-value(Changes before and after cycloplegia) | |||
|---|---|---|---|---|---|
| Tropicamide group | -0.424(P < 0.001) | -0.405(P < 0.001) | -0.341(P = 0.004) | ||
| Compound tropicamide group | -0.408(P = 0.001) | -0.420(P = 0.001) | -0.190(P = 0.154) | ||
Discussion
The cause of myopia remains unknown, and once it develops, it cannot be reversed. Therefore, early prevention and treatment are crucial. CT thinning occurs early in the development of myopia, and CT can be used as a marker of myopia progression [12], and measurement of CT can be a further indicator of potential risk for myopia. Jin et al. [13] included 118 children aged 7–12 years in a 1-year longitudinal study and found that CT was reduced in children with myopia progression when retinal thickness was unchanged or increased, suggesting that choroid thinning of the choroid may precede retinal thinning. Tian et al. [14] found that a thinner temporal choroid at age 12 years predicted 1-year axial elongation in myopic students. Therefore, studies of CT may be useful for predicting myopia development in children and adolescents and for monitoring the effectiveness of treatment and prevention of myopia. In our study, we found that CT in the nasal quadrant was significantly thinner than the other regions in both groups, both before and after ciliary paralysis, CT in the temporal quadrant was significantly thicker than the other regions, and CT in the inner circle quadrant was higher than that in the outer circle quadrant. Our results also show that the mean values of CT and SFCT increased before and after drug application in both the tropicamide and compound tropicamide groups, but only the tropicamide group was statistically significant. AL was negatively associated with SFCT in both groups. Overall, tropicamide eye drops can decrease AL while increasing CT when compared to compound tropicamide.
He et al. [15] included 144 healthy children aged 6 to 12 years to investigate the characteristics of Chinese children’s CT, which were assessed by OCTA CT at sub and peripheral macular locations 0.5, 1.5 and 2.5 mm from the central concavity, and found that in the nasal, superior and inferior regions, CT was thicker in locations closer to the central concavity than further away from the central concavity (all P < 0.05); CT in the nasal quadrant was significantly thinner than the other regions (P < 0.01), which is consistent with our study. The thicker CT in the macula than in the other quadrants may be due to the fact that the central concave area of the macula is critical for vision, and the choroid in the macula provides oxygen and nutrients to the retina in the central concave area of the macula.
Several studies have demonstrated an increase in CT following cycloplegia. Zhang et al. [16] conducted a study involving 30 healthy eyes from 30 children. They applied one drop of 1% atropine gel twice daily for one week and observed a significant increase in CT below the central concavity and 1.0 mm from it. Wu et al. [17] studied 25 eyes from 25 children with low myopia, who used 0.01% atropine drops once nightly before bedtime for 12 months. After three months, they found a significant increase in CT below the central concavity, measuring 309.96 ± 70.82 μm compared to the baseline measurement of 297.92 ± 66.31 μm. Wang [18] conducted OCTA in a 3 × 3 mm macular area among 72 myopic patients aged 4–14 years. The results showed an increase in CT across most regions, with a significant increase in SFCT observed after three sessions of eye drops administered at 10-minute intervals for a total of 30 min. SFCT increased from 243.94 ± 65.10 μm to 248.59 ± 69.11 μm (P < 0.001).
In contrast, other studies yielded different results. Öner et al. [19] studied 37 healthy adult subjects who received topical 1% tropicamide drops three times at 10-minute intervals, finding no significant change in CT after 40 min. Cheng et al. [20] observed eight healthy subjects (16 eyes) with a mean age of 30.13 ± 4.12 years using a mixture of 0.5% tropicamide/0.5% phenylephrine hydrochloride and 0.5% tropicamide mixed eye drops, and there was no significant change in the CT of the macula in either group after 30 min. Kobia-Acquah et al. [21] found a 2.5 μ m decrease in mean subfoveal CT after 30 min (p = 0.10), but no significant difference than before cycloplegia (p > 0.05). Kara et al. [22] recruited 90 healthy subjects, age range 20–59 years and randomized them into 1% tropicamide drops group (n = 30), 2.5% phenylephrine drops group (n = 30) and found a significant decrease in SFCT in both groups 45 min after three eye drops.
The results of the above studies were inconsistent in terms of changes in choroid thickness, and the possible reasons for this discrepancy are due to differences in the mode of data analysis, the method of drug drops, the age of subjects, and differences in the individual response after topical eye drops. Our results found a significant increase in CT in the tropicamide group, which may be attributed to the fact that children are highly regulated, and the choroid, as a part of the uvea that is similar to the iris, transmits the force involved in ciliary muscle contraction to the choroid during regulation, and this mechanical force can affect the thickness of the choroid [23]. Thus, we hypothesize that paralysis of the ciliary muscle weakens its contraction during accommodation, leading to an increase in the scleral circumference at the eye’s equator. This results in a decrease in axial length (AL) and an increase in choroid thickness (CT). The thickness changes in the choroid may also be related to the altered tone of [24, 25] in nonvascular smooth muscle cells within the choroidal, which receives autonomic innervation, may effect changes in the choroidal structure.
The ocular biological parameters were also changed somewhat after cycloplegia. Firstly, our study found a significant SE reduction after cycloplegia. Children’s lenses are more elastic and better adjusted, so after cycloplegia, myopia caused by accommodation decreases and refraction drifts toward hyperopia. Consistent with the study by Li et al. [26] and Wilson et al. [27]. Furthermore, our study found no significant change in IOP before and after cycloplegia. This may be due to the wider anterior chamber angles and deeper anterior chambers in children, along with their strong lens regulation, which likely prevents an increase in IOP after rapid pupil dilation. Ho et al. [28], Wu et al. [29] and Tsai et al. [30] similarly found no difference in IOP before and after cycloplegic agent application. We also found decreased LT and deepened of ACD after cycloplegia. Cycloplegia may cause the iris to move to the periphery, increasing the tension on the suspensory ligament of the lens and thinning of the LT; the iris cristae moves backward, resulting in transient deepening of the ACD. The results of Chang et al. [31], Tsai et al. [30] and Gao et al. [32] are consistent with our study.
AL is the distance from the front of the cornea to the retinal pigment epithelium, so accurate CCT measurements are crucial for assessing changes in the eye’s axis. Zhou et al. [33] showed that CCT was negatively correlated with the rate of SE progression (R=-0.65) and the rate of AL growth (R=-0.47). Furthermore, a thinner CCT may be associated with faster myopic progression. The Pediatric Eye Disease Investigator Group [34] found that the CCT became thinner by an average of 1 μm for each additional diopter of myopic refractive error (P < 0.001). We speculate that CCT may be a predictor of myopic progression. Zeng et al. [35] included 240 eyes of 120 subjects and used compound tropicamide ophthalmic solution to puncture the eyes every 5 min for 3 times which showed an increase in CCT after 1 h, which was eliminated after 4 h of puncture. Chang et al. [31] found that the WTW (0.42 ± 0.43, p < 0.001) distance was widened after cycloplegia. The increase in CCT after cycloplegia may be due to eyelid closure, which causes corneal hypoxia and results in corneal epithelial edema. Moreover, the eye drops come into direct contact with the corneal epithelium, disrupting the tight junctions within the epithelial cells of the tear film and resulting in corneal tissue swelling. The impact of this corneal edema diminishes as the drug is metabolized, allowing the CCT to revert after approximately 4 h. The possible mechanism for the increase in WTW after cycloplegia is that cycloplegia with iris convergence to the periphery during cycloplegia may enhance the difference between the iris and the sclera more pronounced, so the detection edge is closer to the iris and scleral interface, which will make the WTW measurement after cycloplegia greater than before cycloplegia. Our study demonstrated both CCT and WTW increased after cycloplegia, but the long-term effects of short-acting cycloplegia on CCT and WTW need further investigation.
Meanwhile, the elongation of the ocular axis primarily drives the progression of myopia; as age increases, the stroma within the eye becomes more rigid [36], making axial length less prone to change. Children, on the other hand, have more pliable eyes that are more susceptible to external influences. Arjunan et al. [37] studied 147 children treated with 1% atropine for 4 months, resulting in a significant reduction in axial length of 0.10 mm (P < 0.001). Ho et al. [28] found a mean AL decrease of 0.016 mm (P = 0.008) after 1 week of topical 0.125% atropine. Cheng et al. [38] prospectively recruited 114 right eyes of 114 participants (9.1 ± 2.8 years old) and showed a reduction in AL (p < 0.0001) after 30 min of application of 0.4% tropicamide. In our study, we observed AL was reduced in both groups, consistent with the above findings. The axial length can be reduced after application of the cycloplegic agent.
In addition, the results of our study show that as the AL decreases, SFCT tends to increase. AL before and after cycloplegia in both groups was inversely associated with SFCT. Woodman et al. [39] measured the thickness of the sub-macular choroid in 37 subjects, and found an increase in AL with concomitant choroid thinning (p < 0.05) after a 30-minute 4D accommodation task given to myopic patients, suggesting a correlation. On the contrary, the short-acting cycloplegic agent reduced AL and increased SFCT, may delay the progression of myopia to some extent. Additionally, applying it in the evening has no impact on the daily activities of children and adolescents. Before and after the ciliary muscle paralysis, the changes in AL and the changes in SFCT were weakly associated in the tropicamide group, and there was no correlation between the changes in AL and the changes in SFCT in the compound tropicamide group. The weak correlation between the changes in AL and the changes in SFCT before and after medication may be due to the smaller magnitude of AL and SFCT changes caused by drugs. However, in the two groups, although the correlation betweenthe changes in AL and the changes in SFCT in the tropicamide group was weakly related, it was stronger than the compound tropicamide group and was more effective in changing SFCT. At the same time, the difference in the tropicamide group was statistically significant, suggesting that compared with compound tropicamide, tropicamide eye drops can reduce AL while increasing CT.
In this study, both drug groups resulted in a decrease in axial length and an increase in choroid thickness; however, there was no statistically significant difference in the effect of compound tropicamide on choroid thickening. Atropine can cause choroid thickening, possibly by acting on anti-muscarinic receptors in the choroid, which may increase choroid thickness through the modulation of dopamine release [5]. Tropicamide has an anti-acetylcholine effect similar to that of atropine, so it may also show a similar effect. Nickla et al. [40] performed double parasympathetic neurectomy on 4–5 weeks old chicks and found that their choroid membrane was significantly thickened after the operation. It is hypothesized that tropicamide may also cause choroid thickening by blocking the parasympathetic nerves. Compound tropicamide contains tropicamide and phenylephrine hydrochloride, in addition to the effect of tropicamide, phenylephrine hydrochloride can stimulate the sympathetic receptors of the pupillary sphincter, due to the vasoconstrictive effect of sympathomimetic drugs, this effect may offset the thickening of the choroid thickness of tropicamide, resulting in the compound tropicamide on the thickness of the choroid was less, although the mean value increased, the difference was not statistically significant. Compared with compound tropicamide, tropicamide eye drops can reduce AL and increase CT, which may have a certain role in controlling the development of myopia.
Our study included tropicamide and compounded tropicamide eye drops and compared the effects of both on ocular biological parameters and choroid thickness. The study utilized the advanced SS-OCTA device and graphical quantitative analysis software, which employs an automatic stratification technique that reduces manual measurement errors and enhances result accuracy. However, some children were too young to cooperate during the examination, leading to challenges in obtaining accurate measurements. At the same time, in this study, we only observed the temporary effects of the drug, and was not remeasured after the disappearance of the drug effects, so we did not further investigate the long-term effects of the drug on ocular biological parameters and choroidal thickness.
Conclusions
Some ocular biological parameters were altered after application of short-acting cycloplegic agent tropicamide and compound tropicamide to paralyze the ciliary muscle. Compared with compound tropicamide, tropicamide eye drops can reduce axial length while increasing choroid thickness.
Acknowledgements
This study was supported by grants from the Key Project of Anhui Educational Committee (Grant no.KJ2021A0718), the Key Project of Bengbu Medical University (Grant no.2020byzd141), the Project of Graduate Scientific Research and innovation Project of Bengbu Medical University(Byycx23117), and the General Project of Anhui Provincial health Commission (Grant no.2016QK057).
Author contributions
Mengyue Xu: Writing-original draft, Data Curation, Investigation, Methodology, Software. Na Li: Writing-Review, Data Curation, Methodology. Yan Liu: Investigation. Yaru Chen: Investigation. Shuping Xie: Resources, Software. Jianfeng Wang: Project administration, Resources, supervision.
Funding
The Key Project of Anhui Educational Committee (Grant no.KJ2021A0718), the Key Project of Bengbu Medical University (Grant no.2020byzd141), the Project of Graduate Scientific Research and innovation Project of Bengbu Medical University(Byycx23117), and the General Project of Anhui Provincial health Commission (Grant no.2016QK057).
Data availability
Data is available on request from the authors.
Declarations
Ethics approval and consent to participate
The research was approved by the Ethics Committee of The First Affiliated Hospital of Bengbu Medical University (ethics approval number: 2024331), complies with the principles of the “Declaration of Helsinki”. Informed consent form to participate was obtained from all participants’ parents or legal guardians.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
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Mengyue Xu and Na Li contributed equally to this work.
Contributor Information
Shuping Xie, Email: 544407168@qq.com.
Jianfeng Wang, Email: wangjianfeng1969@163.com.
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Data Availability Statement
Data is available on request from the authors.