Optimal dosage of cyclopentolate 1% for cycloplegic refraction in hypermetropes with brown irides

Abstract

To find the optimal dosage of cyclopentolate 1% for cycloplegic refraction in hypermetropes with brown irides, we investigated the difference in cycloplegic auto-refractions obtained after one, two, and three instillations in the same patient. The mean hypermetropia found after three instillations was statistically significantly more compared to that found after one instillation. There was no statistically significant difference in the mean hypermetropia between two and three instillations. There was no significant effect of gender, age, and the presence and type of horizontal deviation. These observations suggest that two drops of cyclopentolate 1% 10 min apart are sufficient for cycloplegic refraction in hypermetropes.

No consensus exists on the optimal dosage of cyclopentolate for cycloplegic refraction.[^1–8] It is important to study a multi-dosage approach to find out the lowest number of instillations of cyclopentolate required to produce adequate cycloplegia with minimum systemic side effects. Studies on the optimal dosage of cyclopentolate are few and have been conducted with two different dosage schedules in the same patient.[⁹¹⁰] There is no study with three different dosage schedules of cyclopentolate in the same patient. We believe that age, refractive error, iris pigmentation, and ocular deviation are the potential confounding variables with a possible effect on measured hypermetropia, as mentioned by Bagheri et al.,[¹⁰] also. We also believe that using one, two, and three instillations of cyclopentolate in the same patient can eliminate these variables.

To find out the lowest and the optimal dosage of cyclopentolate for cycloplegic refraction, we compared hypermetropia found after one, two, and three instillations in the same patient with brown irides.

Materials and Methods

This study included 51 hypermetropes (25 males and 26 females) with brown irides who attended the strabismus service, and were approved by our institutional review board. The age of the 51 patients ranged from 6 to 20 years (mean, 12.48 ± 3.76). A histogram of age is shown in Fig. 1. A total of 41 (80%) patients had esotropia, 6 (12%) had exotropia, and 4 (8%) had orthophoria. All patients underwent auto-refraction (Huvitz MR-3100P, Korea) with cyclopentolate 1% first after instillation of one drop, 1 week later after instillation of two drops 10 min apart, and further 1 week later after instillation of three drops 10 min apart. Auto-refraction was performed after 60 min in patients with one instillation, after 50 min of the last drop in patients with two instillations, and after 40 min of the last drop in patients with three instillations. Thus all patients had auto-refraction after 60 min of the first instillation. The examiner was not blinded to the number of instillations received. The information was recorded on a separate proforma at each visit and the results of previous auto-refraction were not revealed to the examiner. Three measurements were taken and then the average was calculated. Ocular side effects of cyclopentolate including severe redness and itching, and systemic side effects including visual hallucinations, incoherent speech, ataxia, amnesia, or faulty orientation were recorded at each visit. Spherical equivalent refractive errors were documented. Wilcoxon's signed rank test was used to see the difference in the mean hypermetropia found after one, two, and three instillations of cyclopentolate 1%. The mean hypermetropia found after one, two, and three instillations of cyclopentolate was analyzed in relation to gender using the Mann–Whitney test, and using the Kruskal–Wallis test in relation to patient age and the type of squint. A P-value less than 0.05 was considered statistically significant.

Figure 1: Histogram showing the distribution of age

Results

Table 1 presents the mean hypermetropia found in the right and left eyes after one, two, and three instillations of cyclopentolate 1%. Considering three instillations as our gold standard that is supposed to reveal the highest hypermetropia, we compared one and two instillations to three instillations. In the right and left eyes, the mean hypermetropia found after three instillations was significantly more compared to that found after one instillation (Z = –4.369; P = 0.0001 and Z = –3.959; P = 0.0001, respectively, Wilcoxon's signed rank test). There was no statistically significant difference in the mean hypermetropia between two and three instillations in both right and left eyes (Z = –1.032; P = 0.302 and Z = –1.170; P = 0.242, respectively, Wilcoxon's signed rank test). A difference of more than 0.5 D was seen in four eyes between one and two instillations, one eye between two and three instillations, and six eyes between one and three instillations.

Table 1: Hypermetropia found after one, two, and three instillations of cyclopentolate 1%

The mean hypermetropia found after one, two, and three instillations of cyclopentolate 1% with respect to gender, age, and the type of squint is presented in Tables 2, 3, and 4, respectively. There was statistically no significant difference in the mean hypermetropia found after one, two, and three instillations of cyclopentolate 1% between male and female, among age groups 6-10, 11-15, and 16-20 years, and among esotropes, exotropes, and orthotropes.

Table 2: Mean hypermetropia found after one, two, and three instillations of cyclopentolate 1% with respect to gender

None of our patients developed any ocular or systemic side effects of cyclopentolate after one, two, and three instillations.

Table 3: Mean hypermetropia found after one, two, and three instillations of cyclopentolate 1% with respect to patient age

Table 4: Mean hypermetropia found after one, two, and three instillations of cyclopentolate 1% with respect to the type of squint

Discussion

Bagheri et al.,[¹⁰] divided their patients into three groups and compared the cycloplegic effect of cyclopentolate 1% between one and two drops (Group 1), two and three drops (Group 2), and one and three drops (Group 3). They did not find a significant difference among these groups and concluded that a single drop of cyclopentolate was sufficient for cycloplegic refraction. In our study, though the mean difference in hypermetropia between one and three instillations was less than 0.25 D, this was still statistically significant. We did not find a significant difference in the mean hypermetropia between two and three instillations. These observations indicate that one instillation of cyclopentolate 1% does not cause adequate cycloplegia and is, therefore, insufficient for cycloplegic refraction in hypermetropes with brown irides. Furthermore, these observations also suggest that two instillations of cyclopentolate 1% are sufficient for cycloplegic refraction in hypermetropes with brown irides. Bagheri et al.,[¹⁰] had various confounding variables (such as age, refractive error, iris pigmentation, and the presence and type of ocular deviation) equally distributed in the three groups and did not find a significant effect of these on refraction. We also did not find a significant effect of gender, age, and the presence and type of horizontal deviation on hypermetropia in our patients with brown irides. We believe that using different dosage schedules of cyclopentolate in the same patient and then comparing the refractive results is the best method for eliminating the influence of these variables, as done in this study.

Gadioux-Madern et al.,[⁹] recorded the refractive results after the instillation of two drops of cyclopentolate 0.5% 10 min apart and three drops 5 min apart in the same patient in non-strabismic children. They concluded that the former schedule was as effective as the latter. However, in strabismic children, they recommended instillation of three drops. As our patients were enrolled from strabismus service and not from general ophthalmic practice, there were very few patients without strabismus. We did not find a significant effect of esotropia, exotropia, and orthophoria on hypermetropia detected after one, two, and three instillations of cyclopentolate 1% in the same patient.

Various drug complications after one, two, and three instillations of cyclopentolate 1% have been observed in 5%, 11%, and 25% of the patients, respectively.[¹⁰] We were surprised to find that none of our patients had any ocular or systemic side effects of cyclopentolate with all three dosage schedules.

Based on our observations in this study, we suggest two instillations of cyclopentolate 1% at a 10-min interval for cycloplegic refraction in hypermetropes with brown irides.

The authors thank Dr. Suresh K. Sharma, Department of Statistics, Punjab University, Chandigarh, for performing statistical analysis of this study.