. Author manuscript; available in PMC: 2009 Mar 1.

Published in final edited form as: Am J Ophthalmol. 2008 Jan 16;145(3):556–561. doi: 10.1016/j.ajo.2007.10.028

Table 1.

Levels of stereoacuity showing equivalent log seconds of arc values, and where they follow a logarithmic progression. Actual levels tested on Frisby Davis Distance (FD2), Distance Randot (DR), Frisby and Preschool Randot (PSR) stereo tests are indicated by a checked box.

Seconds of arc	Log of seconds of arc	FD2 test levels	DR test levels	Frisby test levels	PSR test levels
20	1.30	√^*
40	1.60	√^*		√	√
60	1.78		√	√	√
80	1.90	√^*
100	2.00		√^*	√^*	√^*
160	2.20	√^*
200	2.30	√	√^*	√^*	√^*
400	2.60	^†	√^*	√^*	√^*
800	2.90		^†	^†	√^*
1600	3.20				^†

= Stereoacuity levels coinciding with logarithmic steps.

^†

= Value assigned to represent ‘Nil’ since it follows the logarithmic progression. The next highest 0.3 log increment was chosen to represent nil for each test, because the highest measurable level differs between tests. Choosing the same log value to represent nil for all tests would introduce bias when comparing differences between tests, for example the difference between the highest measurable level and nil.