The Latest Retinal Disease Diagnostic Devices
The Latest Retinal Disease Diagnostic Devices
The following technology facilitates retinal disease diagnosis, enhancing patient care and your practice's reputation.
Robert J. Murphy, Contributing Editor
Recent advances in retinal disease diagnostic devices are enabling eyecare practitioners to identify subtle changes in pathology that not that long ago eluded detection. As a result, patients at risk for retinal disease-associated vision loss are being discovered earlier, allowing for the preservation of vision.
Here, retina experts discuss these recent advances.
Digital fundus cameras
Digital fundus cameras and their associated software have paved the way for enhanced resolution and magnification and a wide field of capture. Also, most of these devices allow you to create a montage of images that display multiple views of the retina, so you can monitor change in pathology through time. The most recent additions to this technology are multiple spectral images and autofluorescence imaging, says Jerome Sherman, O.D., a distinguished teaching professor at the State University of New York College of Optometry in New York, NY.
Multiple spectral image systems employ light-emitting diodes (LEDs) each with their own spectral color to penetrate different depths of the retina all the way to the choroid, he says. For example, deep red and infrared LEDs penetrate well into the choroid, unmasking disorders, such as an early choroidal melanoma, often invisible to ophthalmoscopy, explains Dr. Sherman.
Autofluorescence is an indicator of the aging pigment lipofuscin found within the retinal pigment epithelium (RPE). RPE abnormalities adversely affect the overlying photoreceptors. Specifically, the absence of a normal glow may signal an overall retinal degeneration, such as retinitis pigmentosa, says Dr. Sherman. For example, autofluorescence imaging may help you detect early evidence of age-related macular degeneration (AMD), and, thus, discuss with the patient the importance of lifestyle changes and the benefits of the age-related eye disease study formulation, should the patient make a good candidate for it. (See “Supplements for AMD,” article.) Panoramic autofluorescent imaging devices are also now available, allowing the clinician to image 200° of the fundus in a single image, Dr. Sherman says.
Excessive autofluorescence, or hyperautofluorescence, is likewise a danger sign, says Dr. Sherman. “Hyperfluorescence means that the retinal pigment cells are sick and stressed. And typically, cells that are sick and stressed will eventually die,” he explains.
As a result, the technology is also ideal for detecting evidence of geographic atrophy (GA) of the RPE, an advance form of non-exudative or “dry” AMD, Dr. Sherman says. He adds that zones representing GA appear black with this technology.
Spectral-domain ocular coherence tomography
As with standard OCTs, spectral-domain, or SD-OCTs, provide cross-sectional images and retinal thickness measurements (with normative databases) useful for diagnosing optic nerve diseases, such as glaucoma — they reveal the retinal nerve fiber layer and ganglion cell complex — and those diseases affecting the macula and elsewhere in the retina. Specifically, they penetrate to all retina layers, which is useful for diagnosing retinal degenerations involving the RPE and its associated photoreceptors in conditions, such as retinitis pigmentosa, cone dystrophies, vascular occlusive disease, achromatopsia and acute zonal occult outer retinopathy, explains Dr. Sherman. Also, these devices can help you identify the particularly important photoreceptor integrity line (PIL) layer overlying the RPE Virtually all patients who have a photoreceptor degeneration have an abnormal PIL, Dr. Sherman says.
In addition, SD-OCTs “perform 1,000 A-scans in .04 seconds, they acquire images in large blocks of the retina, allowing for 3D imaging, and they allow you to segment out [isolate specific layers of the retina],” explains Mark T. Dunbar, O.D., director of optometric services and optometry residency supervisor at the Bascom Palmer Eye Institute, which has multiple locations in Florida. “For example, if you wanted to look specifically at the RPE or the ganglion cell layer, you could isolate that particular layer of the retina, which may be helpful in the diagnosis of various retinal diseases and glaucoma.” He adds that SD technology also provides three-to-five microns of resolution, giving you enhanced detail.
Further, SD-OCTs can be invaluable in monitoring for retinal and RPE changes secondary to hydroxychloroquine sulfate, USP (Plaquenil, Sanofi-Aventis), a drug commonly prescribed to treat autoimmune diseases, such as lupus and rheumatoid arthritis, Dr. Dunbar says. Whereas previously clinicians would monitor these patients annually with visual fields, color vision and Amsler grid testing, clinicians now monitor potential Plaquenilinduced retinal toxicity using SDOCT, fundus autofluorescence or multifocal electroretinography, research shows.1,2,3
Macular pigment optical density meters
Recent research has shown that the macular pigment, which consists of the carotenoids lutein, zeaxanthin and meso-zeaxanthin, serves as a filter over the photoreceptors protecting them from harmful UV radiation, a risk factor for AMD. Further, this research shows that one's macular pigment optical density (MPOD) measurement can indicate the patient's risk for AMD.4,5 Due to these findings, MPOD measuring devices have become available.
“These tests enable you to pick up precursor signs of impending macular degeneration, so you can then give patients a head start on taking the necessary steps, such as changes in diet, changes in lifestyle, or nutritional supplementation, to forestall its development,” says Jeffrey D. Gerson, O.D., a private practitioner in Shawnee, Kan.
The currently available MPOD measurement devices have all been shown to reveal diminished macular pigment long before the appearance of drusen or other evidence of AMD via heterochromatic flicker photometry (HFP). HFP is a subjective psychophysical technique that employs flickering blue-green LEDs and an array of target sizes, to produce a density (e.g. MPOD unit) between 0 to 1.6. A low MPOD measurement is indicative of AMD risk.
Something else to consider: Because research has shown that macular light flash vision recovery measurements can indicate early macular conditions, technology is now available that uses photo-stress testing to aid in retinal disease detection.
Preferential hyperacuity perimetry (PHP) systems
PHP systems detect the conversion from non-exudative (“dry”) AMD to the neovascular (“wet”) form of the disease via visual hyperacuity, or Vernier acuity, instead of visual acuity, to determine visual object misalignment. Visual hyperacuity has been shown at least 10 times more sensitive than visual acuity.6
“The idea behind PHP is that instead of identifying a choroidal neovascular membrane when the patient's vision is 20/400 and he can't read anymore, you pick up changes before a person ever notices it,” explains Dr. Gerson.
PHP devices measure the central 14° of visual field, detect visual object misalignments in the magnitude of three-to-six seconds of arc and provide 82% accuracy for detecting choroidal neovacularization. Finally, PHP has been found to maintain a low false-positive rate (8.1%).7 To use a PHP device, the patient points to flashing dots on a touch screen that have a deviating signal on distinct areas of the macula.
One PHP system designed for home use provides a daily means for patients to check for signs of conversion. The patient hooks the device into a phone line or cellular modem, and the data from each daily test is automatically sent to a live, ongoing data-monitoring center, which then posts the data on a secure website, where the patient's eyecare practitioner can review it. When the data-monitoring center notes a statistically significant change in test scores, the patient and doctor are notified immediately via phone.
These devices can help the eyecare practitioner to differentiate a choroidal nevus from a potential melanoma, detect a retinal detachment or other anomaly through opaque media, such as a dense cataract — protecting one from malpractice lawsuits — and they're ideal for the retinal evaluation of pregnant women, who shouldn't be dilated, say those interviewed. The most recent advancement to this technology: Some are portable and handheld, facilitating their use and allowing for the examination of patients who have physical disabilities.
“The latest devices are comprised of portable probes that attach to any computer via a USB port, and the USB ports also allow you to store images, share them with patients and e-mail them to colleagues,” explains Dr. Sherman. He adds that he encounters indications for ultrasound use a few times a week.
Out with the old?
With these latest devices, one can't help but wonder whether the traditional retinal disease diagnostic devices, such as the slit lamp biomicroscope and associated condensing lenses, are now obsolete. Not so fast, say those interviewed.
“I think it's important that the clinical exam start with ophthalmoscopy because the findings of the ophthalmoscopy guide you to the other retinal disease diagnostic devices you may want to take advantage of,” says Dr. Gerson.
Diana Shechtman, O.D., an associate professor at Nova Southeastern University College of Optometry, in Fort Lauderdale, Fla. adds, “We never want to lose our clinical skills. After all, they are the reason we were able to diagnose and monitor retinal disease before all this technology became available, and they are the reason we're able to use this technology to make management decisions.” OM
1. Kelmenson AT, Brar VS, Murthy RK, Chalam KV. Fundus autofluorescence and spectral domain optical coherence tomography in early detection of Plaquenil maculopathy. Eur J Ophthalmol. 2010 Jul-Aug;20(4):785-8.
2. Chen E, Brown DM, Benz MS, et al. Spectral domain optical coherence tomography as an effective screening test for hydroxychloroquine retinopathy (the "flying saucer" sign). Clin Ophthalmol. 2010 Oct 21;4:1151-8.
3. Aliferis K, Mermoud C, Safran AB. [Multifocal electroretinography in followup of patients treated with hydroxychloroquine]. J Fr Ophtalmol. 2011 Sep;34(7):468-75. Epub 2011 May 6.
4. No authors listed. Macular pigment and healthy vision. Optometry. 2009 Oct;80(10):592-8.
5. Howells O, Eperjesi F, Bartlett H. Measuring macular pigment optical density in vivo: a review of techniques. Graefes Arch Clin Exp Ophthalmol. 2011 Mar;249(3):315-47. Epub 2011 Jan 8.
6. Loewenstein A, Malach R, Goldstein M, et al. Replacing the Amsler grid: a new method for monitoring patients with age-related macular degeneration. Ophthal. 2003 May;110(5):966-70.
7. Stur M, Manor Y. Long-term monitoring of age-related macular degeneration with preferential hyperacuity perimetry. Ophthalmic Surg Lasers Imaging. 2010 Nov-Dec;41(6):598-606.
|Mr. Murphy is a freelance writer based in the Philadelphia area. He has spent several years reporting on the eyecare field. E-mail him at rmur email@example.com. Or send comments to firstname.lastname@example.org.|
Optometric Management, Issue: December 2011