Swept-source optical biometer for axial length measurements in low-resource settings

Abstract

Purpose : The purpose of the work was to study the reproducibility of the axial length measurements obtained with a low-cost swept source OCT biometer in reference to a commercial biometer (IOL Master 500, ZEISS, Jena, Germany).

Methods : A low-cost thermally tuned VCSEL at 850nm has been used for setting up a swept-source optical biometer. The system produces A-scan rates of 2-100kHz with approximately 300µW on the cornea. At 2kHz a depth range of 5cm is achieved with a roll-off of less than 3dB and an axial resolution of 50µm. 41 Eyes (23 healthy volunteers and 18 cataract patients) were imaged in the scope of an ongoing prospective observational study. The axial length (AL) has been extracted as the distance from corneal front reflex to the first retinal peak (ILM). For the extraction a series of A-scans was recorded and arranged into M-scans that allowed for a convenient extraction of relevant parameters and an estimation of the correct retinal position. Cataract grading was performed according to LOCSIII. The agreement of the measurements with the commercial reference system was assessed using a Bland-Altman plot and 95% limits of agreement.

Results : Axial length has been successfully measured in all study participants. The patient group covered LOCSIII grading from 1-5+. Figure 1 depicts the Bland-Altman plot, comparing the AL values obtained with the IOL Master 500 with the values measured with the VCSEL biometer, and calculated using the Haigis formula. Figure 2 shows the linear fit of data (AL measured with IOLM500 vs optical value for AL measured with the VCSEL biometer). Current precision or standard deviation of AL measurements for the VCSEL biometer is given by the axial resolution. A lower SNR of the retinal peak resulted in higher AL standard deviation. However, more sophisticated peak detection algorithms should allow for precisions better than 10 µm, as is the case in modern biometry systems with a similar axial resolution.

Conclusions : The price of SS-lasers hinders the availability of SS-based optical biometers in low resource settings. We developed a low-cost optical biometer based on a tunable single mode VCSEL diode. First results show that the AL measurements of the new SS-OCT biometer correlate well to those of the commercial biometer. Thus, VCSEL biometer has the potential to be used as a cost-effective alternative for pre-operative examination of cataract patients in low-resource settings.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.