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Imaging devices yield early detection, track progression
Today’s armamentarium of diagnostic instruments provides more accuracy, ease of use and patient satisfaction than ever before, according to practitioners. In choosing from among these instruments, optometrists should determine which device is best suited to the diagnostic needs of their particular practice.
“All of the instruments right now are very good,” said Murray Fingeret, OD, a Primary Care Optometry News Editorial Board member based in St. Albans, N.Y. “They have all made great leaps forward. From there, it really depends on a clinician’s own philosophy.”
The GDx: earlier detection
Laser Diagnostic Technologies’ GDx NFA is a confocal scanning ophthalmoscope with an integrated polarimeter. Rather than measuring topography or height of the retina, the GDx uses infrared laser technology to measure the thickness of the nerve fiber layer. This provides information about the extent of glaucoma damage. Because retinal nerve fiber layer damage can be present up to 6 years before visual field damage, the GDx is considered useful in early detection.
“The GDx provides significantly earlier detection of glaucoma than other conventional tests,” said Gary Gerber, OD, a practitioner in Westwood, N.J. “It measures the thickness of the retinal nerve fiber layer, and a lot of data suggest that this changes before other things we test – like peripheral vision, for example.”
GDx measurements are compared to a normative database, which enables the practitioner to compare the two eyes to each other, as well as to compare the current visit with previous visits.
The GDx is also quick and easy to operate, Dr. Gerber said. “Our staff learns how to use it in a day,” he said. “It is easy for them to use and easy for us to interpret.”
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The HRT II: change probability
Heidelberg’s HRT II measures the surface topography of the optic nerve and retina. It uses a confocal scanning laser to scan a patient’s optic nerve and generate a high-resolution, 3-D image of the optic nerve head.
“The HRT II can give the height of the area adjacent to the retina,” Dr. Fingeret said. “So it measures the topography of the area around the optic nerve as well as the optic nerve.”
Ease of use is a distinct advantage, particularly with the HRT II, Dr. Fingeret said. “Once you get it centered, you press a button, and you’re done,” he said. “Everybody can use it. That is one difference between the HRT and the HRT II.”
According to Dr. Fingeret, the main feature that sets the HRT II apart from all other glaucoma imaging devices is a program called Glaucoma Change Probability. Researcher Balwantray Chauhan created the program about 10 years ago, initially as a research tool.
“Let’s say you take a measurement of the nerve fiber layer thickness or the size of the cup, and then you redo the test 6 months from now and find that it appears to have gotten worse,” Dr Fingeret said. “That may not be the case, because there is a certain amount of instrument variability, or instrument error.”
“Dr. Chauhan measured the amount of change in normal subjects over the course of a month,” Dr. Fingeret said, “and he found the amount of change that is inherent.”
Dr. Chauhan also found that, to properly measure change, three readings of successive change are necessary, said Dr. Fingeret. “The bottom line for all of these instruments is that it is important to follow or manage for progression or change,” he said. “In many ways, that is more important than making the initial diagnosis.”
The OCT3: “analogous to ultrasound”
The Zeiss Humphrey Optical Coherence Tomography scanner provides cross sectioning of the retina. It is considered similar to ultrasound, but uses a light source of broad band width, super luminescent diode light instead of sound.
“It is analogous to ultrasound,” said Dixon Golden, OD, a practitioner based in Center, Texas. “I tell my patients that we are doing ultrasound on their retinas and optic nerves, but we are using light waves instead of sound waves.”
Dr. Golden said the OCT3 measures the topography of the optic nerve head, performs a nerve fiber layer analysis and scans the macula.
“It has a multi-variant diagnostic approach,” he said. “You can actually look at the nerve fiber layer, topography of the disc and macular pathology like macular holes, cystoid macular edema and diabetic macular edema.”
Dr. Golden said the OCT3 is very useful in determining structural evidence of the development of glaucoma prior to visual field loss. “That puts us ahead of the curve instead of behind,” he said. “Roughly 40% of the nerve fiber can be lost before we pick up a field defect, and then we have lost half the battle before we get started.”
Dr. Golden said the instrument is very easy to use and very patient-friendly. “My technicians use it, and there is no pain to the patient. It takes about 4 to 5 minutes,” he said. “Also, we are finding that we don’t have to dilate nine out of 10 of our patients. It is really helping us put the pieces of the puzzle together.”
The Optomap: undilated exam
The Optos’ Panoramic200 is a non-mydriatic ophthalmoscope that can capture an ultra wide-field image of the fundus in 0.25 seconds. This information is then processed into a full-color composite image, the Optomap, which can be viewed and enlarged.
“It is all performed on an undilated pupil in a quarter of a second,” said William Jones, OD, a Primary Care Optometry News Editorial Board member based in Albuquerque, N.M. “It is useful in screening for any abnormalities of the fundus. When you know how to use it correctly, it is amazing what you can find in the macula and the optic nerve, all the way out to the equator.”
Dr. Jones said he has used the instrument to find pigmented lesions, retinoschesis, retinal breaks, lattice degeneration, neovascularization of the disc and retina, and drusen in the periphery and posterior pole.
“It can find just about everything,” he said. “But one thing it is really good at finding is pigmented lesions in the eye, because you can see the pigmented lesion against the whole background of the eye. It sticks out like a sore thumb.”
The Optomap Exam is also easy to use, Dr. Jones said, taking less than 5 minutes to image both eyes.
“Patients are very pleased that they do not need to be dilated,” he said. “They also enjoy seeing the inside of their eyes. You can describe to a patient what is going on in his or her retina, but most of it is over their heads unless they see an image of it.”
According to Roy Sanchez, a fourth-year optometry student at the Southern California College of Optometry who recently studied with Dr. Jones, the Optomap Exam has been an invaluable tool in his education.
“It has been a great learning tool for me – I have been able to see all of the posterior pole and out past the equator,” he said. “And patients love it – they are excited not to have to be dilated. Patients come in asking for it – it is a great internal marketing tool.”
Talia’s RTA: providing diverse data
Talia’s Retinal Thickness Analyzer combines the features of a digital fundus camera, a computerized scanning slit lamp and a retinal thickness analyzer. It is used for such diverse cases as early glaucoma detection, retinal thickness analysis of diabetic retinopathy and visualization of retinal pathologies.
“It is unique in that it analyzes the nerve head and the retina in a number of different ways,” said Eric Schmidt, OD, a practitioner in Elizabethtown, N.C. “It analyzes not only topographically, but also by providing stereometric or parametric types of data not available with some other instruments.”
Dr. Schmidt said the RTA also provides excellent data on both the optic nerve head and the posterior pole of the retina. “So I am not just locked into analyzing tissue based on nerve fiber layer thickness or disc topography,” he said. “I can look at the tissue a number of different ways and analyze it clinically.”
Dr. Schmidt said he has been especially impressed with the instrument as a means of detecting retinal or macular pathology. “For instance, we have all had cases where a patient has decreased vision and a metamorphopsia on Amsler grid,” he said. “And we examine the retina, we see a macular problem and we’re not sure whether it is a macular hole, a macular cyst or a pseudohole.”
In this situation, Dr. Schmidt said he has found that he can scan the patient with the scanning laser on the RTA and determine whether there is focal thickness, a focal depression or cystic changes. “And not only does it give me a 3-D type of analysis and a topographical analysis, it also gives me what is called a slit report, so that I can see the slit beam as it is being projected onto the retina.”
Dr. Schmidt said he has also used the RTA for imaging the nerve fiber layer and the macula to pick up early thinning in the peripapillary zone and in the papillomacular bundle zone.
“I am rapidly becoming convinced that this is the first area that is affected in normal tension glaucoma,” he said. “That’s why we see changes in the nerve before the visual field, because the nerve fiber layer is becoming somewhat atrophic. This instrument highlights these changes exquisitely.”
For Your Information:
- Murray Fingeret, OD, is a Primary Care Optometry News Editorial Board member based in St. Albans, N.Y. He can be reached at St. Albans VA Hospital, Linden Blvd. and 179th Street, St. Albans, NY 11425; (718) 526-1000; fax: (516) 569-3566. Dr. Fingeret has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any of the companies mentioned. He receives honoraria to speak for Heidelberg and Zeiss Medtec.
- Gary Gerber, OD, can be reached at 372 Kinderkamack Road, Westwood, NJ 07675-1653; (201) 796-2021; fax: (201) 666-8032. Dr. Gerber has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any of the companies mentioned.
- Dixon Golden, OD, can be reached at 702 Louisiana Street, Center, TX 75935; (936) 598-8501; fax: (936) 598-2311. Dr. Golden has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any of the companies mentioned.
- William Jones, OD, is a Primary Care Optometry News Editorial Board member based in Albuquerque, N.M. He can be reached at 1828 Conestoga Road, Albuquerque, NM 87123; (505) 293-7347; fax: (505) 247-2153. Dr. Jones has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any of the companies mentioned.
- Eric Schmidt, OD, can be reached at 409 East Broad Street, Elizabethtown, NC 28337-8807; (910) 862-4268; fax: (910) 862-2057. Dr. Schmidt has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for Talia Technology.
- The GDx NFA is available from Laser Diagnostic Technologies, 10864 Thornmint Road, San Diego, CA 92127-2402; (800) 722-6393; fax: (858) 673-7909; Web site: www.laserdiagnostic.com.
- The HRT II is available from Heidelberg Engineering Inc., 1499 Poinsettia Ave., Suite 160, Vista, CA, 92083; (800) 931-2230; fax: (760) 598-3770; Web site: www.heidelbergengineering.com.
- The OCT3 is available from Zeiss Humphrey Systems, 5160 Hacienda Drive, Dublin, CA 94568; (925) 557-4544; fax: (925) 557-4319; Web site: www.czos.com.
- The Optomap Exam, made possible by the Panoramic200, is available from Optos North America, 199 Forest Street, Marlborough, MA 01752; (877) 455-8855 ext. 100; fax: (508) 486-9310; Web site: www.optos.com.
- The Retinal Thickness Analyzer is available from Talia Technology, Ltd., 4519 George Road, Suite 120, Tampa, FL 33634-7329; (813) 887-1917; fax: (813) 887-5909; Web site: www.talia.com.