The traditional evaluation of accommodative function (Table 1.5) involves measurement of the amplitude of accommodation using either Donder’s push-up method or the Optometric Extension Program (OEP) minus lens procedure. There are shortcomings to this limited approach, however. In recent years, many authors have reported the clinical significance of testing accommodative response and facility as well as amplitude (22,51–56). An important concept is that an individual may experience asthenopic symptoms and have an accommodative disorder even when the accommodative amplitude is normal (53,55). Several studies have investigated the relationship between accommodative facility and the presence of symptoms. Both Hennessey et al. (55) and Levine et al. (56) reported that symptomatic subjects perform significantly poorer than asymptomatic subjects on both monocular accommodative facility (MAF) and BAF testing.

Liu et al. (53) and Cooper and Feldman (47) were able to objectively measure changes in latency and velocity of accommodative response before and after vision therapy. They found that accommodative dynamics changed significantly after vision therapy. The fact that accommodative facility results are related to symptoms, and that changes can be demonstrated after therapy, suggests that it is a valuable assessment technique. It should be part of the routine evaluation of accommodative function.

The third aspect of the evaluation, accommodative response, has also been studied (57–60). It has been demonstrated that the accommodative response is generally not equal to the stimulus. Because most optometric testing relies on stimulus measures and assumes equality between stimulus and response, a clinician might be misled when managing binocular or accommodative anomalies. It is, therefore, important to actually measure the accommodative response. MEM retinoscopy is a widely used procedure that can be utilized for this assessment. Rouse et al. (59,60) have demonstrated the validity of MEM retinoscopy and established normative data.

Another clinical method of assessing accommodative response is Nott retinoscopy (61,62). In contrast to MEM retinoscopy, in which lenses are used to neutralize the reflex, in Nott retinoscopy the examiner moves the retinoscope toward or away from the patient until neutrality is observed. Goss et al. (63) studied the interexaminer reliability of MEM and Nott retinoscopy on 50 young adult subjects. The results of their study indicated close agreement of the means for MEM and Nott. There was a wider range of measurements with MEM retinoscopy than with Nott retinoscopy.

Wick and Hall (64) studied the relationships among the three areas of accommodation (amplitude, facility, and response) that are usually tested. They screened 200 children and, after eliminating those who had strabismus or significant uncorrected refractive error, found that only 4% had deficits in all three of the accommodative functions. Their results suggest that it is impossible to predict the results of one test based on the results of another. Therefore, when accommodative dysfunction is suspected, all aspects of accommodation, amplitude, facility, and response must be considered.

A complete assessment of accommodation should include all three components just described. A suggested minimum database would include the amplitude of accommodation, accommodative facility, and MEM retinoscopy. Table 1.6 lists the expected findings for all accommodative testing described next.

1. Purpose To subjectively measure the amplitude of accommodation under monocular conditions.

(a) Careful measurement of distance It is critical to accurately measure the distance at which the patient reports a blur. Even small errors in measurement can lead to large differences in results. For example, an endpoint at 5 cm (2 in.) suggests a 20 Δ amplitude, whereas a blur at 6 cm (2.5 in.) suggests an amplitude of 16 Δ. To reduce this problem, the push-up amplitude can be measured through −4.00 D lenses. This modification moves the endpoint further away from the patient and allows more exact measurement of the endpoint.

(b) Monitor patient response With young children, it is important periodically to ask the child to read the letters to be sure that the print is not blurred. One modification in procedure that can be used is to begin the test with the chart very close to the child. Instead of asking when the print blurs, pull the chart away from the child until he/she can first read the letters. A study comparing the results of using the traditional push-up method of assessing the amplitude of accommodation to the pull-away method found no significant difference in the measurement (65).

(c) Relative distance magnification A problem associated with the push-up method is that the letters no longer subtend the angle expected for a 20/30 letter because of relative distance magnification. A 20/30 letter at 40 cm becomes equivalent to a 20/60 letter at 20 cm and a 20/120 letter at 10 cm. The push-up test, therefore, overestimates the accommodative amplitude. Hamasaki et al. (66) found that the overestimation is about 2 D. A possible solution to this problem is to change the size of the letters at 20 cm and again at 10 cm.

3. Expected values A variety of norms can be used for monocular accommodative amplitude. Tables developed by Duane and Donders provide expected findings by general age (33). A more commonly used system is Hofstetter’s formula, which is based on Duane’s figures (67). The average amplitude at any age can be calculated using this formula: 18.5 − 1/3 age. The minimum amplitude expected for a given age can be calculated using 15 − 1/4 age.