Comparison of Three Swept-source Optical Coherence Biometry Devices in Long and Short Eyes

Accurate and repeatable biometric measurements are essential in providing an optimal refractive outcome.

ss-OCT biometry uses a tunable wavelength laser source to scan the eye, this technology showing its superiority through better signal-to-noise ratio, the wavelength light source being projected into the eye, one at a time; thus improving tissue penetration.

A previous study reported that the AL differs between adults was due mainly to the difference in vitreous cavity. The longer the AL becomes, the longer the posterior vitreous body becomes and the Argos defines the vitreous refractive index as 1.336. Therefore it is possible that the equivalent refractive index used in the IOLMaster 700 exceeds 1.336. Omoto et al. showed that the comparison of the arithmetic prediction errors between the Argos and IOLMaster 700 indicated that both biometers showed a myopic trend and the median arithmetic prediction errors were closer to zero with the Argos, the longer the AL became, this trend became more marked, suggesting that the Argos showed a significant hyperopic trend, especially with longer ALs.

This might show the advantage of using segmental refractive index instead of equivalent refractive index in longer ALs. Nevertheless, the authors did not include short eyes (<22mm) and longer AL (>32mm), thus further studies should be needed.

The aim of the study is to compare the agreement and repeatability of AL measurement using three different ssOCT devices in short (<22.5mm) and long eyes (>25.5mm).

This a prospective, randomised, observational study that would include patients (42 eyes of 42 patients) which attended pre-surgical examination. A written informed consent will be obtained from each patient.

Only one eye from each patient will be included in the study. All patients included in the study will undergo biometric measurements in a random fashion with the three devices (IOLMaster 700, Argos and Anterion Heildelberg). Each patient will be measured three times with each device and between the measurements they will be asked to blink or keep their eyes closed for tear film recovery and to avoid fatigue. Scans that pass the quality requirement of each device will be taken for analysis.

The order in which the measurements will be performed (Anterion, IOLMaster 700 or Argos) will be randomised using randomised.org.

Patients will be measured 8 weeks (+/-2 weeks) postoperatively with the three devices and the postoperative examination will also contain visual acuity, autorefraction and subjective refraction.

Each patient will receive the same type of lens (standard IOL, Clareon, Alcon). Inclusion criteria

• Written informed consent
• 21 years old or above
• age-related cataract
• AL<22.5 mm or >25.5 mm (long or short eyes) Exclusion criteria
• patients with dense cataract (LOCS grading III) or mature cataract
• corneal pathology that would significantly influence biometric measurements
• nystagmus or pathologies that would affect patient fixation
• pregnancy- for women in reproductive age a pregnancy test will be performed.
• Main outcome: Limits of agreement (1.96xSD) between the optical biometers for the AL (mm) data
• Secondary outcomes:
• Subgroup analysis for the refractive outcome (SEQ) after 8 weeks (+/-2 weeks) in short (<22,5mm) and long eyes (>25,5mm).
• Limits of agreement (1.96xSD) between the optical biometers for the following variables: keratometry (Ks, Kf, Km), CCT (µm), ACD (mm), LT (mm),
• Duration (seconds) of measurement time and total time (including data entry)
• Evaluation of the Barrett (and Haigis formulae with the 3 devices (mean of actual vs. mean of predicted SEQ)
• Repeatability coefficient (within subject standard deviation - SD) and coefficient of variation between the three devices