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Today’s diagnostic tools become more useful for detecting retinal disease
Many of the diagnostic instruments that analyze the posterior segment are able to perform multiple functions and can yield valuable information in terms of retinal and macular disease.
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Instruments such as the Heidelberg Retinal Tomograph (HRT II, Heidelberg Engineering), the Optical Coherence Tomographer (OCT3, Carl Zeiss Meditec), the Panoramic200 Optomap Retinal Exam (Optos) and the Retinal Thickness Analyzer (RTA, Talia Technologies), all can be used for the diagnosis of various retinal conditions.
“We can look forward to these technologies continuing to improve with time. Their use, I believe, will continue to increase,” said Robert P. Wooldridge, OD, FAAO, who practices at the Eye Foundation of Utah in Salt Lake City. “In a clinical setting, they are extremely valuable in helping to diagnose retinal problems.”
The HRT II : elevation map of the retina
The HRT II is a retinal topography instrument that uses confocal laser imaging to provide a three-dimensional image of the optic nerve and retina, providing information on diameter, depth and thickness.
Dr. Wooldridge said the HRT II can be quite useful in diagnosing retinal disease. He said this instrument is capable of providing a detailed view of the macula. “The HRT II scans the macula and generates a topography map of the macula,” he said. “It gives us an overview of the macular surface detail.”
This allows the practitioner to see possible areas of scattered edema, such as what might be observed in diabetic macular edema. “The HRT II gives us an elevation map of sorts,” he said. “It enables us to see areas of elevation of the retinal surface.”
Heidelberg has also added a Macular Edema Module (MEM) for its HRT II. The MEM gives the surface topography, and also adds the capability of measuring diabetic and cystoid macular edema. The Macular Edema Module measures three-dimensional light reflectance from the retina.
This software analyzes the light intensity profile of each location or data point within the 3-D image and measures its width. The width of the light intensity profile has been shown in clinical trials to correlate with retinal thickness.
Dr. Wooldridge emphasized the HRT II’s ability to give an analysis of the macula in terms of retinal elevation. “The HRT II does an excellent job with that,” he said.
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The OCT3: cross-section of retina
Another instrument useful for diagnosing retinal disease is the OCT3. This instrument is similar to ultrasound, but uses a light source (850 nm) or broad-band (40 nm) wide super luminescent diode light instead of sound.
Dr. Wooldridge said the OCT is excellent for its optic nerve and retinal analysis. “The OCT gives us a cross-section of the retina, which can be across the fovea, and various orientations or directions,” he said. “It does not give us a surface topography, but it gives a good cross-section.”
Dr. Wooldridge gave an example, citing a patient who has subretinal fluid as part of a disease called central serous chorioretinopathy.
“The OCT would show that very nicely,” he said. “It can also show retinal edema or subretinal hemorrhage. The detail from the OCT has been a great benefit in the analysis of various phases of macular holes.”
Historically, Dr. Wooldridge said, the analysis of the retina has been performed basically by slit-lamp examination with a diagnostic lens, such as a 60-D or 90-D lens. Ophthalmoscopy, either direct or indirect, has also been used. The OCT does not replace the need for a careful dilated examination, but supplements the information gained during the clinical evaluation.
“The OCT gives us the benefit of looking underneath the surface of the retina and telling us if there is truly retinal edema or retinal elevation, such as hemorrhage fluid or neovascularization,” he said.
The Optomap retinal exam
The Optomap retinal exam is made possible by the Panoramic200, a nonmydriatic scanning laser ophthalmoscope.
“There are two monochromic lasers that can scan the retina,” said Thomas Phillips, OD, a practitioner located in Warminster, Pa. Dr. Phillips said the red laser is 633 nm and the green laser is 532 nm.
“The laser scans the retina, both vertically and horizontally, in less than 1 second (0.25 seconds actual time), through an undilated pupil,” he said. “So, because of the way the instrument works, you can have a full, 200° view of the fundus through a pupil as small as 2 mm in size.”
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Dr. Phillips said the Optomap exam’s resolution goes to within 20 micrometers in the central field, and within 40 micrometers in the peripheral field of view.
“When you look at it, the green channel separation shows you the vasculature of the retina very prominently,” Dr. Phillips said. “When you look at that separation, if there are any leakages or hemorrhages, you can actually see those hemorrhages as large black dots or a large black area if it is a pre-retinal hemorrhage.”
The red channel separation looks at the deeper layers of the retina, Dr. Phillips said, enabling the detection of melanomas and tumors.
Dr. Phillips added that the Optomap exam has good sensitivity and specificity. He cited a study performed at Tufts University by William Jones, OD.
“The study showed that the sensitivity was equal to or superior to a binocular indirect exam,” he said. “Also, with a binocular indirect, you have intra-examiner variability. With the Optos, you can have five different technicians take the image, and it’s going to be the same. It works very well.”
RTA: wide range of uses
The RTA multi-purpose system, which combines the benefits of a digital fundus camera, a computerized scanning slit lamp and a retinal thickness analyzer, enables acquisition, display and analysis of retinal optical cross-sections and provides registered maps of retinal thickness and comparative reports. Talia has recently introduced an add-on module for a digital fundus imaging system.
RTA slit images also enable visualization of retinal pathologies such as macular holes, cysts and membranes.
According to David A. Cockrell, OD, FAAO, a practitioner based in Stillwater, Okla., the RTA does an effective job of detecting various retinal disorders.
“Our practice includes a sizable number of people with retinal problems — hypertension, retinopathy, as well as diabetic retinopathy,” he said. “We want to be able to more readily identify the onset of retinal or macular edema. We have found that the RTA is unbelievably accurate in this capacity.”
Dr. Cockrell said the RTA technology has caused him to send patients out for fluorescein angiography with retinal specialists more quickly than he would have otherwise.
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“The retinal specialists we refer to have been very pleased with the earlier diagnosis,” he said. “They are very surprised that the technology is as accurate as it is in diagnosing subretinal and intraretinal edema or lesions.”
Dr. Cockrell said he has also used the RTA to identify diabetic macular edema, cystoid macular edema, retinal holes, retinal cysts and retinoschisis.
“It is excellent at diagnosing retinal edema, and it is also very helpful in diagnosing early glaucoma,” he said. “It picks up macular changes related to loss of ganglion cells, which occurs with glaucoma.”
For Your Information:
- Robert P. Wooldridge, OD, FAAO, can be reached at Eye Foundation of Utah, e-mail: rpwod@aol.com.
- Thomas Phillips, OD, can be reached at the Eyecare Center, e-mail: eyecare@pil.net.
- Dr. Phillips has no direct financial interest in the products mentioned in this article. He is a paid consultant for Optos.
- David A. Cockrell, OD, FAAO, can be reached at e-mail: dacockrell@cockrelleyecare.com. Neither Dr. Wooldridge nor Dr. Cockrell has a direct financial interest in the products mentioned in this article, nor are they paid consultants for the companies mentioned.
- The HRT II is available from Heidelberg Engineering Inc., Vista, Calif.; (800) 931-2230; (760) 598-3770; Web site: www.heidelbergengineering.com.
- The OCT3 is available from Carl Zeiss Meditec, Dublin, Calif.; (925) 557-4100; Web site: www.humphrey.com.
- The Optomap retinal exam is available from Optos, Marlborough, Mass.; (877) 455-8844, ext. 100; e-mail: info@optos.com; Web site: www.optos.com.
- The RTA is available from Talia Technology Inc., Tampa, Fla.; (800) 214-2030; Web site: www.talia.com.