RT Journal
A1 Mathew JA, Shah SA, Simon JW
T1 VArying difficulty of snellen letters and common errors in amblyopic and fellow eyes
JF Archives of Ophthalmology
JO Archives of Ophthalmology
YR 2011
FD February 14
VO 129
IS 2
SP 184
OP 187
DO 10.1001/archophthalmol.2010.369
UL http://dx.doi.org/10.1001/archophthalmol.2010.369
AB Objective 
    To investigate the varying difficulty of Snellen letters in children with amblyopia.Methods 
    We tabulated the letter-by-letter responses of amblyopic and nonamblyopic fellow eyes on random, computer-generated Snellen lines. Participants were 60 children, aged 5 to 13 years, with a history of amblyopia. Main outcome measures were relative difficulties of Snellen letters and common misidentifications.Results 
    Errors were 7.5 times more common with certain letters (B, C, F, S) than with others (A, L, Z, T), this difference increasing to 17.6-fold at threshold. Similar relative letter difficulty was demonstrated at lines above and at visual acuity thresholds, and both difficult and easy letters were the same for amblyopic and nonamblyopic fellow eyes. Specific misidentification errors were often repeated and were often reciprocal (eg, B for E and E for B).Conclusion 
    Since therapeutic decisions in amblyopia management are often based on small differences in visual acuities, the relative difficulties of letters used in their measurement should be considered. The Early Treatment Diabetic Retinopathy Study system should be considered for use in this clinical setting.