Fluctuations of Steady-State Accommodation Is a Marker for Screening Spasm of Near Reflex

Abstract

Purpose: To determine the utility of root mean squared (RMS) deviations of steady-state accommodation as a noncycloplegic marker for spasm of near reflex (SNR) vis-à-vis regular refractive errors.

Methods: Binocular steady-state responses of accommodation, pupil, and vergence of 20 patients with accommodative spasm subtype of SNR (SNR-A; 9-23 years) and 91 with regular refractive errors (29 emmetropes, 41 myopes, 21 hyperopes; 19-38 years) was recorded in the uncorrected refractive error state for 120 seconds using a dynamic (50 frames per second), infrared photorefractor. Mean and RMS deviation of raw data was calculated for three 20-second-long epochs and their diagnostic utility was determined using standard ROC curves.

Results: RMS deviations of accommodation increased with mean refractive error in SNR-A (y = -0.23x + 0.38; r2 = 0.69; P < 0.001) and regular refractive error (y = -0.02x + 0.10; r2 = 0.14; P = 0.002) cohorts, albeit with steeper slope and higher y-intercept in the former rather than the latter cohort. RMS deviation of 0.19D reliably distinguished SNR-A from regular refractive errors with a sensitivity and specificity of 95.2% and 92.2%, respectively [mean (±1 SEM) area under ROC curve: 0.98 ± 0.01]. The sensitivity, specificity, and area under ROC curve for RMS deviations of pupil (66.7%, 80%, and 0.70 ± 0.09) and vergence (52.4%, 84.6%, and 0.68 ± 0.08) were smaller than accommodation.

Conclusions: RMS deviations of steady-state accommodation is a robust noncycloplegic marker for differentiating SNR-A from regular refractive errors. Pupil and vergence fluctuations have limited utility in this regard.

Translational relevance: RMS deviations of accommodation may be easily obtained using commercial photorefractors, and the cut-off values reported herein may be implemented to identify SNR-A during refractive error screening.

Figure 1.

Raw traces of right eye's accommodation (panels A–C), pupil diameter (panels D–F), and binocular vergence eye position (panels G–I) plotted as a function of time for three representative subjects, one each with emmetropic refraction (left panels), myopic refraction (middle panels) and SNR-A (right panels). While data was collected for 120 seconds from each subject, data worth only 60 seconds is displayed here. The ordinate scales are different for each panel to best represent the details in the data. All data reported here were collected without the subject's refractive correction in an otherwise dimly lit room.

Figure 2.

Scatter diagram of the RMS deviation of right eye's accommodation plotted as a function of the corresponding mean accommodative state in the SNR-A and regular refractive error cohorts.

Figure 3.

Panel A shows receiver operating characteristics (ROC) curves for RMS deviation of accommodation, pupils, and vergence along with the respective mean (±1 SEM) area under the curve values. The ROC curve for accommodation with the resampled data of the regular refractive error cohort is also showed in this panel. Panel B shows the ROC curves for three different refractive error cohorts compared against the SNR cohort. All other details are same as panel A.