White-To-White
The white-to-white is the measurement of the distance between the two limbal area horizontally. The mean IOLMaster white-to-white is 11.76 (range: 10.6 -12.7, sd 0.451) for an n=116. The Mean white-to-white for the LENSTAR with the same n=116 is 11.82 (range 7.5-14.52, sd 1.004). The difference between these two measurements was not statistically significant with a P=0.506. As it may be evident in the chart below, the means do not reflect the head to head comparison. When looking at the median the IOLMaster median was 11.7 mm and the LENSTAR median was 11.98 mm.
Discussion of the White-To-White Results:
When taking the six sample eyes and taking the extremes of range produced by the IOLMaster as 10.5 and 12.5 mm, the Holladay II formula produced the table below.
The extent of the influence of the white-to-white seems to be comparable to the anterior chamber depth difference of 1.0 mm as discussed previously. It must be reiterated that the IOLMaster had a range of 10.6 mm to 12.7 mm with a SD of 0.451 which was clinically reasonable. The LENSTAR had a range of 7.50 mm to 14.52 mm with SD of 1.004. From a clinical standpoint, the numbers produced by the LENSTAR must be reject as there was neither an eye as small as 7.50 mm nor as large as 14.52 mm in this series of patients.
The two instruments produced similar means but the range of results by LENSTAR is very concerning. The influence of the White-To-White can be as powerful as the Anterior Chamber Depth. This modest effect has been clearly understated in the clinical circles!
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