Comparison of ocular biometry measurements by applanation and immersion A-scan techniques

Abstract

PurposeThe study compared ocular biometry values using applanation and immersion techniques to determine the most applicable method for our tertiary training centre where personnel with different levels of experience and expertise in biometry take measurements used in calculation of required intraocular lens before cataract surgery.MethodsThe study was a prospective cross-sectional comparative study of different techniques of ocular biometry from diagnostic equipment (biometry probe 10 MHz Sonomed® A-scan (PACSCAN 300A, USA). Measurement variables were obtained among children and adults undergoing cataract surgery. Scleral (Prager) shell was used for the immersion technique followed by the contact technique by the same examiner.ResultsThe biometry values of 92 eyes of 92 adult were taken. Their ages ranged from 18 to 95 years with a mean of 64.7 (SD ± 12.9) years. There were 55 (59.8%) males and 37 (40.2%) females, with a male to female ratio of 1.5:1.Average axial length (22.0–24.4 mm) eyes were the most common eyes measured in 75 (81.5%) of the cases. The means of the axial lengths biometry values with immersion and contact technique were 23.66(±1.36) and 23.46 mm (±1.46); the axial length differences was 0.2 ± 0.26 mm (range 0.0–0.94 mm) and statistically significant (95% CI of the Difference 0.15 to 0.26, p = 0.000). The Standard deviation SD (mm) of Individual Eye Axial Length showed a mean of 0.03 ± 0.04 (0.0–0.3) mm for immersion and for contact technique 0.14 ± 0.12(0.0–0.6)mm.ConclusionThere was a significant difference in ocular biometry measurement with the contact and immersion ultrasound techniques. The immersion technique had better repeatability, thus it is ideal in a training hospital setting in a typical in sub-Saharan Africa who have limited resources to employ a dedicated person to do biometry; and where the different operators of A-scan machines have different levels of experience and expertise.

A-scan biometry, phacoemulsification, and foldable intraocular lens implantation in a young orangutan (Pongo pygmaeus)

“…A-scan ultrasound biometry was useful for intraocular structure measurements, such as the AL, anterior chamber depth (ACD), and lens thickness (LT), that are used to calculate the power of intraocular lenses ( Ademola-Popoola et al ., 2015 ). AL in children can be measured using either a contact or immersion technique ( Wilson and Trivedi, 2012 ).…”

“…There is a paucity of the published report of phacoemulsification in non-human primates, such as spider monkeys, gorillas, chimpanzees, pygmy marmosets, chacma baboons, and orangutans ( Whitley et al ., 1980 ; de Faber et al ., 2004 ; Clouser, 2010 ; Montiani-Ferreira et al, 2010 ; Leiva et al ., 2012 ; Warwick et al ., 2017 ). Ocular biometry is a useful technique for the preoperative calculation of the intraocular lens (IOL) diopter power ( Ademola-Popoola et al ., 2015 ). However, some non-human primates have undergone surgery by phacoemulsification with IOL implantation without the IOL power calculation.…”

Improved refractive outcomes of small-incision extracapsular cataract surgery after implementation of a biometry training course

“…While others have reported lower prediction error than achieved in our study,[16171819] it is notable that those studies used immersion A-scan or partial coherence interferometry, which have a higher accuracy and repeatability than applanation A-scan ultrasound. [202122] This is primarily due to the variable corneal indentation that inevitably occurs during applanation. Those studies also used phacoemulsification which may improve the refractive outcomes due to a more predictable capsulorrhexis and subsequent effective IOL position.…”

Evaluation of Axial Length Measurement Using Enhanced Retina Visualization Mode of the Swept-Source Optical Coherence Tomography Biometer in Dense Cataract

“…Although US biometry is effective in measuring AL especially in patients with advanced cataract, in whom an optical biometer cannot measure AL, it also has some disadvantages, such as the following: (1) variations in the measured values owing to contact with the cornea, (2) the immersion method requires higher technical expertise and is associated with a poorer reproducibility than the optical biometer, (3) the visual axis cannot be captured, and (4) the anterior and posterior corneal planes are not separated even by the segmented method, and the measurement of accuracy varies depending on the examiner’s expertise [19].…”