Pitfalls in the conception, manipulation, and measurement of visual accommodation

Reports of applied research in visual accommodation frequently contain points of confusion, suggesting that there may be some widespread misunderstanding regarding the nature of accommodation, the complexities involved in its measurement, and the multiple meanings inherent in its terminology. The present paper reviews several of these problem areas. Included are discussions of the effect of refractive error on accommodation assessment; the dangers involved in assuming equivalence among physiological, refractive power, and conjugate distance changes; and multiple meanings in the conception of resting accommodation. A variety of manipulation and measurement problems also are reviewed, including the specification of accommodative target distance, the use of lenses, and the correction of refractive error. The review concludes with recommendations regarding conceptions and procedures useful in avoiding the difficulties described.