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

PURPOSE: To 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). SETTING: Department of Ophthalmology, Saiseikai Kurihashi Hospital, Saitama, Japan. METHODS: In 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. RESULTS: The 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. CONCLUSION: The 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.

Comparison of 2 optical biometers and evaluation of the Camellin-Calossi intraocular lens formula for normal cataractous eyes.

PURPOSE: To compare the measurements and intraocular lens (IOL) power calculations obtained with an optical biometer (AL-Scan) and partial coherence interferometry (PCI) device (IOLMaster 500), and to evaluate the accuracy of the Camellin-Calossi IOL formula in virgin eyes. SETTING: Saiseikai Kurihashi Hospital, Saitama, Japan. DESIGN: Prospective comparative study. METHODS: Measurements were compared from 262 patients (450 eyes) scheduled for cataract surgery. Axial length (AL), keratometry (K), anterior chamber depth (ACD), and number of eyes that were successfully measured were compared. Comparisons were performed of the residual postoperative refractive error with the SRK/T, Haigis, and Camellin-Calossi IOL formulas with optical biometer data. The IOL constant was optimized for 81 eyes that had iSertMicro 251 IOL implantation. RESULTS: The mean difference in AL between biometers was -0.012 mm ± 0.031 (SD) (P < .0001). Correlation coefficients (r) for AL, keratometry, and ACD were 0.9997, 0.9836, and 0.9571, respectively. The calculated IOL constant for the Camellin-Calossi formula was 119.3. The optimized IOL constant for the SRK/T was 118.8, the same as that of the User Group for Laser Interference Biometry for the PCI device. For the Haigis formula, only a0 was optimized, and it was 1.390. After optimizing the A-constant for the Camellin-Calossi formula, the residual postoperative refractive error of the Camellin-Calossi formula was not statistically significantly different in comparison to those obtainied with the Haigis and SRK/T formulas. CONCLUSION: Ocular biometry measurements were equivalent for both devices, indicating that the AL-Scan can be used for routine preoperative cataract assessment. The predictive accuracy of the Camellin-Calossi formula included in the optical biometer was equivalent to common IOL formulas for virgin eyes. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.