Objective real-time measurement of instrument myopia in microscopists under different viewing conditions

While instrument myopia is known to occur when microscopes are used, little is known about the accommodation response during microscopy, or about the factors which may alter the magnitude of instrument myopia. In addition, there has been no real-time objective measurement of instrument myopia during the microscopy task. Twenty inexperienced subjects and 10 experienced microscopists (average work experience of 4.8 years (SD 3.2 yr)) with mean age of 24.1 years (SD 2.9 yr) and 31.2 years (SD 2.9 yr) respectively were recruited to the study. Instrument myopia was measured using an infrared photorefractor (PowerRefractor) under different viewing conditions and microscope settings (with different forms of refractive error correction, changes in target quality, changes in eyepiece power settings, changes in magnification and changes in illumination of the target). Instrument myopia was greater in inexperienced (1.98 D (SD 0.91 D)) than in experienced (1.38 D (SD 0.75 D)) microscope users. There was no statistically significant change in the level of instrument myopia under the different viewing conditions or different microscope settings, and there were large individual variations. Other factors may play more of a role in determining the degree of instrument myopia during microscopy than the task variables altered here.