How is the astigmatism axis of the eye measured?
Nov 19, 2025
Source: Cainiu Health
Dr. Wang Lei
Introduction
Astigmatism axis measurement is generally performed using methods such as automated refractometry. The optometrist operates the autorefractor, instructing the subject to fixate on a target image within the instrument. Using optical principles, the device captures refractive information from the eye and quickly provides an initial measurement of the astigmatism axis and degree. This method is simple to perform and time-efficient, commonly serving as a preliminary screening tool and providing reference data for subsequent precise refraction.
Measurement of astigmatism axis is generally performed using methods such as an automated refractor, comprehensive refraction system, corneal topography analysis, Jackson cross-cylinder test, and subjective trial lens refraction. Detailed explanations are as follows:
1. Automated Refractor Test: The optometrist operates the automated refractor by having the examinee fixate on a target image within the instrument. Using optical principles, the device captures ocular refractive information and quickly provides a preliminary measurement of astigmatism axis and degree. This method is simple and fast, commonly used as a screening tool to guide subsequent precise refraction.
2. Comprehensive Refraction System Examination: The examinee sits in front of the phoropter while the optometrist adjusts combinations of lenses, asking the individual to compare clarity of different visual targets to gradually refine the astigmatism axis value. This approach incorporates the examinee's subjective feedback, yielding more accurate results than automated refractors, making it suitable as a core step in refraction.
3. Corneal Topography Analysis: The instrument captures images of the corneal surface and generates a corneal topography map, determining the astigmatism axis based on variations in corneal curvature. This method is especially useful for patients with irregular corneal shapes, providing a comprehensive view of the cornea and helping identify the cause and distribution of astigmatism.
4. Jackson Cross-Cylinder (JCC) Test: Based on initial refraction findings, the optometrist uses a cross-cylinder lens to fine-tune the cylindrical axis, asking the examinee to judge whether visual targets appear clearer or distortions reduced under different axis orientations. Through repeated comparisons and adjustments, the optimal axis that provides the clearest vision with minimal distortion is determined, further refining the measurement accuracy.
5. Subjective Trial Lens Refraction: Based on preliminary data, the optometrist inserts trial lenses with varying astigmatic axes into a trial frame, which the examinee wears while observing visual targets and reporting visual experiences. The optometrist adjusts the lens axis iteratively according to feedback until the examinee achieves clear and comfortable vision, thereby confirming the precise astigmatic axis.
To measure astigmatism axis accurately, individuals should visit正规 ophthalmology clinics or professional optometry centers where trained professionals operate specialized equipment. Prior to testing, prolonged eye use should be avoided to prevent measurement inaccuracies due to eye fatigue. If corrective lenses are needed after examination, both axis and refractive power must be precisely incorporated into the prescription to ensure proper lens alignment with the eye’s refractive status.
