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Ultrasound biometry provides more information than external measurements alone
New devices using the technology can provide accurate measurements of the internal corneal layers and anterior segment structures.
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Compared with external measurements alone, devices that use ultrasound biometry technology can provide ophthalmologists with excellent images of the anterior chamber and posterior chamber of the eye.
Very high frequency (VHF) digital ultrasound takes ultrasound biomicroscopy to the next level over hand-held models in terms of image quality, accuracy, ease of use and functionality, Dan Z. Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO, told Ocular Surgery News.
“VHF digital ultrasound can image the anterior chamber and the posterior chamber, including visualization behind the iris, which has until now been a part of the anterior segment that most surgeons have been operating within effectively in the dark. Measurements can be made of anatomic structures, such as anterior chamber depth, angle-to-angle width and sulcus-to-sulcus width, and pathologic structures, such as solid masses and cysts. But most importantly, the new Insight 100 device (ArcScan) also enables measurement of the whole crystalline lens for the first time, due to the ingenious scanning motor design that uses six degrees of freedom,” Reinstein said.
Useful for refractive surgeons
Reinstein has used VHF digital ultrasound since 1993, developing a series of prototypes on which the Insight 100 was based. He has described numerous corneal and anterior segment applications, most notably applications associated with corneal epithelial thickness mapping such as keratoconus screening, assessing suitability for further hyperopia steepening, and diagnosis and treatment of irregular astigmatism.
The technology is especially useful for comprehensive refractive surgeons, William F. Wiley, MD, told OSN. Wiley uses the Insight 100, an effective tool for refractive cataract surgery, corneal inlay surgery, and cross-linking or corneal strength studies.
The automation of the new technology has led to improved accuracy when compared with devices that use the older technology, Wiley said.
“This device is basically automated, where it is doing a scan of the whole anterior segment and mapping that with software and then overlaying the interpretation. It is much more reliable,” he said.
New mapping abilities
The tool can provide ophthalmologists with total corneal mapping, corneal epithelial thickness mapping and stromal thickness mapping of the eye. These measurements can show a surgeon if a patient is better suited for refractive surgery or for corneal stability intervention, Wiley said.
In addition to the applications related to epithelial thickness mapping, Reinstein said the ability to map the internal layers of the cornea, such as a LASIK flap and residual stromal thickness, has given surgeons clinical applications for laser re-treatment surgeries.
“Mapping the residual stromal thickness is very important for safely planning corneal laser surgery re-treatments as it ensures that the thinnest point can be identified, something that is particularly important for planning hyperopic and custom ablations because the maximum ablation is not necessarily in the location of the thinnest point,” he said.
Better lens placement
In the future, ultrasound biometry may give a surgeon the ability to more accurately place IOLs, Wiley said.
Lens placement can be challenging for even the most experienced surgeons. Surgeons can accurately measure the shape of the anterior segment, the corneal curvature and the actual length of the eye, but it is still difficult to understand and determine where the lens will actually fit in the eye, Wiley said.
“With the anterior segment ultrasound, it can give us a peek into the future about where the lens may fit. If studied properly, and with further understanding, we should have better and more reliable intraocular lens measurement,” he said.
For phakic IOLs, the Insight 100 may improve safety by using direct measurements of posterior chamber dimensions and postoperative monitoring of haptic position as this is one of the main variables that defines the ICL vault above the crystalline lens, Reinstein said.
New information attainable
A “huge amount of important information” can be derived by the ability to visualize and measure the internal corneal layers and the anterior segment structures using this technology, which cannot be done with external measurements alone, Reinstein said.
“In fact, current screening and imaging techniques such as topography, wavefront and corneal thickness profiling can sometimes result in the wrong diagnosis, as we have demonstrated in keratoconus screening and in the management of refractive surgery complications. Similarly, diagnosis and management of anterior segment disease and surgical complications can only be fully understood by direct imaging of the internal structures of interest,” he said. – by Robert Linnehan
- References:
- Kim DY, et al. Am J Ophthalmol. 1998;doi:10.1016/S0002-9394(98)00025-7.
- Lovisolo CF, et al. Surv Ophthalmol. 2005;doi:10.1016/j.survophthal.2005.08.011.
- Reinstein DZ, et al. J Cataract Refract Surg. 2006;doi:10.1016/j.jcrs.2006.08.020.
- Reinstein DZ, et al. J Refract Surg. 2009;doi:10.3928/1081597X-20090610-06.
- Reinstein DZ, et al. J Refract Surg. 2010;doi:10.3928/1081597X-20091105-02.
- Reinstein DZ, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20121210-02.
- Reinstein DZ, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20130719-02.
- Reinstein DZ, et al. Refract Corneal Surg. 1993;doi:10.3928/1081-597X-19930901-12.
- For more information:
- Dan Z. Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO, can be reached at London Vision Clinic, 138 Harley St., London, W1G, 7LA, United Kingdom; email: dzr@londonvisionclinic.com.
- William F. Wiley, MD, can be reached at Cleveland Eye Clinic, 2740 Carnegie Ave., Cleveland, OH 44115; email: wiley@cle2020.com.
Disclosures: Reinstein reports he is a consultant to Carl Zeiss Meditec and has a financial interest in ArcScan Inc. Wiley reports he is a consultant to ArcScan Inc.