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. Author manuscript; available in PMC: 2018 Dec 1.
Published in final edited form as: Am J Ophthalmol. 2017 Sep 23;184:19–27. doi: 10.1016/j.ajo.2017.09.018

TABLE 4.

Probability of the ISNT rule and its variants occurring randomly

All possible random combinations of the rule variants Probability of random occurrence
ISNT rule ISNT 4.2%
IST rule ISNT, INST, ISTN, NIST 16.7%
IS rule ISNT, INST, INTS, ITSN, ISTN, ITNS, NIST, NTIS, NITS, TISN, TNIS, TINS 50%

Abbreviations: I = inferior; N = nasal; S = superior; T = temporal.