The effect of different targets used on cylindrical axis and power measurement during subjective refraction

Background: Astigmatism is one of the most common type of refractive errors. There are several techniques can be used to measure astigmatism with the most commonly is Jackson Cross Cylinder (JCC). In addition, there are several targets available to be used with JCC such as cluster dots and a single letter on the Snellen chart. The purpose of this study was to compare the effect of using cluster dots and a single letter target on the amount of cylindrical power and axis measured with JCC and investigate the most preferred target by the observer. Method: 100 eyes were tested with the age ranged from 18 to 35 years old (M=22SD=4). Distance visual acuity (VA) was measured by using projected Snellen chart followed by objective (retinoscopy) and subjective refractions. Subjective refraction was performed twice using both the cluster dots and a single letter (of one line larger than the best VA) to measure cylindrical power and axis. Subjects were also asked for their preferred target at the end of the examination. Results: Results showed no significant difference in both cylindrical power (cluster dots: M=0.56DC, SD=0.50single letter: M=0.55DC, SD=0.50) (p=0.973) and axis (cluster dots: M=100o, SD=68osingle letter: M=105o, SD=66o) (p=0.379) obtained using different targets. 66% of the participants have chosen cluster dots as their preferred target, followed by 24% of the participants preferred the single letter target and the remaining 10% had no preference. Conclusion: Measurement of cylindrical power and axis using JCC was comparable between cluster dots and single letter target. Future study comparing this effect on different degrees and types of astigmatism may be conducted to investigate if this result applies to all degrees and types of astigmatism