Influence of the signal-to-noise ratio on the accuracy of IOLMaster measurements

PurposeTo evaluate the relationship between the sound-to-noise ratio (SNR) and the reliability of axial length (AL) measurements obtained with the IOLMaster (Carl Zeiss Meditec AG).SettingDepartment of Ophthalmology, Saiseikai Kurihashi Hospital, Saitama, Japan.MethodsIn a clinical prospective study, 216 consecutive eyes of 144 patients scheduled for cataract surgery were evaluated for the type and severity of cataract using the Lens Opacities Classification System III. Preoperative and postoperative AL measurements were performed with the IOLMaster. The preoperative SNR values were used to divide the eyes into 5 groups. The following were compared between the groups: preoperative logMAR best spectacle-corrected visual acuity (BSCVA), difference in AL between preoperatively and postoperatively, error in the postoperative predicted refraction, and type and severity of cataract.ResultsThe preoperative logMAR BSCVA was significantly worse in eyes with an SNR <2 (P<.05). The AL was longer preoperatively than postoperatively in all groups, and there was a significant difference in the <2 SNR group and the 2 to <5 group (P<.05). There were no significant differences in the error in postoperative predicted refraction. The percentage of patients with P4 or worse posterior subcapsular cataract (PSC) increased significantly with a decrease in the SNR (P<.01). However, there was no correlation between nuclear color grade and the SNR.ConclusionThe SNR value was useful in confirming the good quality of AL readings taken with the IOLMaster, even though the SNR value correlated significantly with the preoperative logMAR BSCVA and PSC severity.