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What Natural Relaxation Drills Can and Cannot Do
Published in John William Yee, The Neurological Treatment for Nearsightedness and Related Vision Problems, 2019
Instrument myopia is a condition where the eye becomes myopic when an instrument is placed over the eye. Any instrument can create the symptom: a microscope, a telescope, or even a phoropter—the optical equipment used to test your vision. The phenomenon is documented, but it was never taken serious. The assumption in optometry is that the neutral shape of the crystalline lens when the eye is occluded is the same as when regarding an object in the distance, but that is not always the case. Some of my participants with high myopia still visit their eye care specialists for follow-up care. During the initial treatment for severe myopia before the rectus muscles totally regained their tension to maintain the improved shape of the eyeball, my colleagues reported that they see worse when tested with a phoropter compared to trial lenses—even when the examination room was well lit.
Less is more: optimal recording time for measuring the steady-state accommodative response
Published in Clinical and Experimental Optometry, 2023
Beatríz Redondo, Jesús Vera, Rubén Molina, Raimundo Jiménez
Accommodation is the active dioptric power change of the eye to maintain a clear image of an object on the retina. There are subjective and objective techniques for measuring the accommodative function, with subjective methods relying on the patient’s perception of blur as an end point criterion, whereas objective methods are primarily based on the assessment of the optical power or refractive status of the eye.1 Objective methods, based on ocular refractometry, provide a more reliable and accurate measure of accommodation, since subjective measures seem to overestimate the accommodative function.2–4 Most autorefractors only measure the distance static refractive error while the eye focuses on internal fixation targets, and these devices have shown to cause instrument myopia.5 However, accommodation is a dynamic process, which requires focus on targets located at different accommodative demands, and fluctuates throughout time when focusing on a stationary target.6
Instant vision assessment device for measuring refraction in low vision
Published in Clinical and Experimental Optometry, 2021
A potential source of error in IVAD refraction is instrument accommodation. Studies of instrument accommodation while using telescope are limited. Substantial instrument accommodation of 1.00 D has been found in subjects viewing through a low power telescope in dim light and empty field condition.18 Bright light conditions are helpful to maintain a relaxed accommodation while using binoculars.19 Decreasing the setting from high convergence (high plus) to exact focus in using single lens reflex cameras has shown to almost cancel instrument myopia.20 Therefore, hyperopic focusing and high illuminance have been incorporated into this study to control instrument accommodation. Under these two conditions, a 2.4x telescope calibrated to measure simulated refractive errors in young adults found that instrument accommodation contributed to an error of 0.13 ± 0.12D, which was clinically insignificant.21 Also, the effect of instrument accommodation is of less importance in low vision because most of the patients are presbyopic.
The Repeatability of Values Measured Using the Spot Vision Screener in Healthy Children and Children with Refractive Errors
Published in Journal of Binocular Vision and Ocular Motility, 2019
Tsukasa Satou, Tsuyoshi Nogami, Yoshiaki Takahashi, Misae Ito, Takahiro Niida
Since hand-held autorefractors can measure refraction without requiring much cooperation from the patient and without fixation of the head, it is used in ophthalmic examination. Since it is portable, it is becoming more essential in pediatric ophthalmology, especially for preschool vision screening. The Retinomax (Right, Tokyo, Japan) is a typical hand-held autorefractor used in Japan. According to a previous report,1 it is highly sensitive and specific in detecting amblyopia during preschool vision screening. However, it is commonly known that when using an instrument such as the Retinomax, in which it is necessary to gaze at a target within the instrument, the refractive value tends to shift towards myopia (instrument myopia), and the refractive value obtained is not accurate.2,3 The examiner needs to interpret the result, considering the instrument myopia on the obtained refractive value. Therefore, an autorefractor that is convenient and portable that can obtain refractive values without being affected by the effect of accommodation is eagerly anticipated.