TY - JOUR
T1 - Quantitative analysis of the accommodative convergence to accommodation ratio
T2 - Linear and nonlinear static models
AU - Hung, George K.
N1 - Funding Information:
Manuscript received February 26, 1996; revised November 22, 1996. This work was supported in part by a grant from Essilor International and in part by the National Institutes of Health under Grants NIH-EY08817 and 07519. The author is with the Department of Biomedical Engineering, Rut-gers University, P.O. Box 909, Piscataway, NJ 08855 USA (e-mail: [email protected]). Publisher Item Identifier S 0018-9294(97)02228-3.
PY - 1997
Y1 - 1997
N2 - Ogle and his colleagues proposed two measures of aculomotor linkage called the accommodative convergence to accommodation (AC/A) ratio. This ratio provided a clinically useful assessment of the drive of accommodation, or focusing system, on vergence, or binocular fixation system. The phoria method measured the relatively large deviation in eye alignment under the monocular condition, whereas the fixation disparity method measured the relatively small misalignment of the eyes under the binocular condition to obtain the AC/A ratio. Ogle et al. indicated that these two measures should be equal. However, experimental results showed a substantial difference between the AC/A ratios obtained by the two methods. To quantitatively assess the difference between the two methods, a linear static model was first evaluated. This model was based on an earlier successful model of the accommodation and vergence system. The linear model solution showed that these two methods were equivalent and thus could not account for the differences found. Then, a nonlinear static model, containing the deadspace operators depth of field and Panum's fusional area (PFA), was evaluated. Since two solutions were possible for each deadspace operator, there were four basic solutions. However, there were two binocular-viewing paradigms. This resulted in four prism-viewing and four lens-viewing solutions. Finally, a difference was taken between the prism- and lens-viewing measures, giving a total combination of 16 solutions. Only four of these solutions were equal to that using the phoria method. Some of the other solution lines were widely separated, thus providing a range of possible data values across different solution lines. Calculations showed that the variation in AC/A ratio values for data across difference solution lines was comparable to that found experimentally. Thus, the deadspace operators in the nonlinear model were able to account for the discrepancy between the AC/A ratio determined by the phoria and fixation disparity methods.
AB - Ogle and his colleagues proposed two measures of aculomotor linkage called the accommodative convergence to accommodation (AC/A) ratio. This ratio provided a clinically useful assessment of the drive of accommodation, or focusing system, on vergence, or binocular fixation system. The phoria method measured the relatively large deviation in eye alignment under the monocular condition, whereas the fixation disparity method measured the relatively small misalignment of the eyes under the binocular condition to obtain the AC/A ratio. Ogle et al. indicated that these two measures should be equal. However, experimental results showed a substantial difference between the AC/A ratios obtained by the two methods. To quantitatively assess the difference between the two methods, a linear static model was first evaluated. This model was based on an earlier successful model of the accommodation and vergence system. The linear model solution showed that these two methods were equivalent and thus could not account for the differences found. Then, a nonlinear static model, containing the deadspace operators depth of field and Panum's fusional area (PFA), was evaluated. Since two solutions were possible for each deadspace operator, there were four basic solutions. However, there were two binocular-viewing paradigms. This resulted in four prism-viewing and four lens-viewing solutions. Finally, a difference was taken between the prism- and lens-viewing measures, giving a total combination of 16 solutions. Only four of these solutions were equal to that using the phoria method. Some of the other solution lines were widely separated, thus providing a range of possible data values across different solution lines. Calculations showed that the variation in AC/A ratio values for data across difference solution lines was comparable to that found experimentally. Thus, the deadspace operators in the nonlinear model were able to account for the discrepancy between the AC/A ratio determined by the phoria and fixation disparity methods.
KW - Accommodation
KW - eye movements
KW - nonlinear model
KW - oculomotor control
KW - simulation
KW - vergence
UR - https://www.scopus.com/pages/publications/0030912053
UR - https://www.scopus.com/pages/publications/0030912053#tab=citedBy
U2 - 10.1109/10.563300
DO - 10.1109/10.563300
M3 - Article
C2 - 9125813
AN - SCOPUS:0030912053
SN - 0018-9294
VL - 44
SP - 306
EP - 316
JO - IEEE Transactions on Biomedical Engineering
JF - IEEE Transactions on Biomedical Engineering
IS - 4
ER -