Measuring the refractive state of an eye based on the intensity of the retinal reflex

When examining the fundus of the eye with an ophthalmoscope, the intensity of the retinal reflex depends on the refractive state of the eye. In this study, application of this phenomenon for measuring the refractive state of the eye is demonstrated. First, a calibration curve relating the intensity of the retinal reflex and the refractive state was obtained using a model eye. Next, the intensity of the retinal reflex was measured while subjects were viewing a checker-board pattern, the distance of which was varied within the range from 0.17 to 1 m. Further, the relation between the refractive state and the optical power of the stimulus could be determined based on the measured light intensity and the calibration curve. Generally, the measured refractive state increased with the optical power of the stimulus. However, blinking and fluctuations in accommodation had undesired effects on the results.