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Comparison between MEM and Nott Dynamic Retinoscopy

Tassinari, John

Optometry and Vision Science: March 2000 - Volume 77 - Issue 3 - p 119
Correspondence

Pasadena, California

Del Pilar Cacho et al. recently reported that the accommodative lag for a near target was greater by almost a factor of 2 with MEM dynamic retinoscopy vs. Nott dynamic retinoscopy. 1 They conclude that this difference is attributable to the insertion of supplementary measuring lenses during MEM, whereas Nott does not require supplementary measuring lenses. The measuring lenses, according to the authors, leads to patient adaptation and thus invalidates MEM as a measure of accommodative response.

An alternative explanation for the difference in accommodative response with MEM vs. Nott is that the MEM method used in the present study biased the MEM method toward more lag. The MEM method employed by the examiner differed from established methods in three ways. First, the test card was suspended from a near-point rod instead of clipping the card to the retinoscope as recommended by Rouse and Ryan 2 and Birnbaum. 3 Second, the subjects looked through a phoroptor during MEM. Rouse and Ryan 2 recommend “normal reading conditions… ” and most clinicians use a trial frame or the patient’s habitual glasses during MEM. A phoroptor is notorious for limiting peripheral vision and one can speculate that constricted peripheral vision would drive accommodation toward its tonic state. Third, the examiner used a lens bar for the supplementary measuring lens in lieu of the recommended loose trial lens. 3 An unwieldy lens bar interposed in front of a phoropter with a nearpoint rod attached to it may have made it difficult to interpose the supplementary measuring lens for the recommended 0.2 s 3 or 0.4 s. 4

Of interest is the experimental result from the present study showing an average accommodative response with Nott retinoscopy of 0.415 D lag. This result compares favorably with previously published average MEM retinoscopy results of 0.23 D lag, 4 0.33 D lag, 5 and 0.50 D lag. 6 Thus, accommodative response per Nott retinoscopy in the present study is equivalent to accommodative response per MEM in previous studies.

John Tassinari

1. del Pilar Cacho M, Garcia-Munoz A, Gar-cia-Bernabeu JR, Lopez A. Comparison between MEM and Nott dynamic retinoscopy. Optom Vis Sci 1999; 76:650–5.
2. Rouse MW, Ryan JM. The optometric examination and management of children. In: Rosenbloom AA, Morgan MW, editors. Principles and Practice of Pediatric Optometry. Philadelphia: Lippincott, 1990.
3. Birnbaum MH. Optometric management of nearpoint vision disorders. Boston: Butterworth-Heinemann, 1993.
4. Rouse MW, Hutter RF, Shiftlett R. A normative study of the accommodative lag in elementary school children. Am J Optom Physiol Opt 1984; 61:693–7.
5. Jackson TW, Goss DA. Variation and correlation of standard clinical phoropter tests of phorias, vergence ranges, and relative accommodation in a sample of school-age children. J Am Optom Assoc 1991; 62:540–7.
6. Locke LC, Somers W. A comparison study of dynamic retinoscopy techniques. Optom Vis Sci 1989; 66:540–4.
© 2000 American Academy of Optometry