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What’s new in diagnostic and test instrumentation?
As physicians begin to treat more diseases and distress to the eye, newer diagnostic and test instruments are giving clinicians a better way to see what’s going on.
In our Spotlight on Diagnostic and Test Instrumentation section, we look at several diagnostic tools that are making an impact in a variety of ophthalmic subspecialties.
Research led by Mihai Pop, MD, compared ultrasound biomicroscopy with caliper sizing of the limbus in determining the proper size of the sulcus for fitting posterior chamber phakic IOLs.
Recent studies have shown that complications after posterior phakic IOL implantation tend to be the result of improper sizing. Typically, sulcus size is determined by measuring the limbus with a caliper and then adjusting the size by adding 0.5 mm for myopic eyes and subtracting 0.5 mm for hyperopic eyes.
The study found that sulcus size did not correlate significantly with limbus size, and therefore the traditional estimation using calipers was inadequate. At no time were sulcus size and limbus size an accurate match. The study found that the difference between the sulcus and the limbus was 0.6 ± 0.7 mm for myopia and 0.3 ± 0.8 mm for hyperopia.
On another front, after decades of IOL implantation by various physicians with various forms of IOLs, it has become increasingly important to be able to identify implanted IOLs when treating other ocular conditions. For instance, silicone oil used in a pars plana vitrectomy may react with a silicone lens.
In a study led by Wayne F. March, MD, it was found that Raman spectroscopy can be used to identify the type of IOL implanted after previous cataract surgery. The Raman spectroscopy uses a confocal system that allows integration depth, by which the Raman scattered light is collected. Each IOL material type gives off a different spectroscopy.
In all cases Raman spectroscopy was able to distinguish the differences among acrylic, silicone and PMMA lenses.
Also within the realm of cataract surgery, a study by Naoichi Horio, MD, showed that a single flash electroretinogram may be able to predict the virulence of organisms that may predispose patients to endophthalmitis after IOL implantation.
His study showed that a rapid decrease in b-wave amplitude in the electroretinogram can be an indicator of highly virulent organisms, which could lead to endophthalmitis. In eyes where the b-wave ratio was less than 1.0, some eyes were diagnosed with Pseudomonas aeruginosa and Enterococcus faecalis.
In the field of glaucoma, research using optical coherence tomography (OCT) has shown that this diagnostic test may be the best currently available.
Christopher Bowd, PhD, compared four different technologies and found that although the OCT was probably not sufficient to warrant use as a sole screening method in the general population, it would be an effective device where treatment options are at a premium.
The study compared the OCT 2000 by Zeiss Humphrey; GDx Nerve Fiber Analyzer by Laser Diagnostic Technologies; the Humphrey Field Analyzer II by Zeiss Humphrey; and the Humphrey Field Instrument using the Welch Allyn FDT by Zeiss Humphrey and Welch Allyn.
When glaucoma was defined as a glaucomatous appearance of the optic disc and standard automated perimetry results were not a criterion, the instrument that best discriminated between healthy and glaucomatous eyes was the OCT.
Finally, retinal diagnosis has another new tool as well. A study by Thomas Friberg, MD, has shown that the Optos Panoramic 200 may be effective in screening for diabetic retinopathy.
The device produces high resolution color digital fundus images with anatomical and pathological detail comparable to an examiner viewing the retina with an indirect ophthalmoscope, all the while without the need for pupillary dilation. It uses a red-green scanning laser and takes approximately 2 minutes to image each eye.
The ongoing study suggests that the Optos system may be the first truly non-mydriatic imaging system, for which there will be no need for dilation.
The editors of Ocular Surgery News