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Suzanne Daly, D Jackson Coleman, Danielle Trief, Ronald H Silverman; Axial Length Measurement by Immersion B-Scan. Invest. Ophthalmol. Vis. Sci. 2019;60(9):484.
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© ARVO (1962-2015); The Authors (2016-present)
Cataract extraction is one of the most commonly performed surgical procedures in the United States. Determination of the corrective power of the intraocular lens implant depends on accurate corneal (keratometry) and axial length measurements. In the presence of clear media, these measurements can be readily obtained optically by instrumentation such as the IOLMaster (Zeiss), as well as axial length measurements by A-scan ultrasonography. However, there are situations in which measurements may be inaccurate or unable to be obtained by these methods. This includes opaque media (corneal opacification, or dense, brunsecent cataracts), extreme axial length measurements (high hyperope or myope, staphyloma), the presence of intraocular silicone oil, and vitreous membranes.
16 eyes of 12 patients were referred to our center for B-scan axial length measurement. Ultrasound images were obtained with the patients lying in supine position and water-bath standoff was achieved using steridrape and warmed saline solution. Barraquer wire lid speculum was used for patients unable to open their eyes sufficiently to obtain images or to do so without squeezing. 10 MHz Quantel Aviso B-scan was used, and a minimum of 5 cineloops of up to 99 images of each eye were obtained in axial orientation. Images were then evaluated and a minimum of 5 images were measured per eye. Measurements were taken of anterior chamber, lens, vitreous and axial length.
The average improvement in visual acuity (VA) was 3.82 ±4.26 Snellen lines. In the group of 8 eyes with dense cataracts, VA improved by 5.13 ±4.01 lines. In the high myopes (4 eyes), the mean improvement was 3 lines, but one patient in this group developed dry AMD, which affected the final visual outcome. A plot of pre- and most recent post-operative VA is provided.
Where extremes of globe size, prior ophthalmic surgical procedures and dense opacities preclude optical or A-scan determination of axial length, immersion B-scan is a useful methodology. Immersion B-scan permits visualization of the cornea, lens and posterior pole, thus facilitating accurate measurement of axial length along the visual axis even where optical opacities, eye shape irregularies and other factors preclude use of standard methods.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Plot of pre- and most recent post-operative VA in Snellen lines. The diagonal line indicates no change, with points below it demonstrating improved VA.
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