SARDs/IMR Diagnosis
SARDSAwareness.org has absolutely no commercial interest and does not endorse products. Please do not construe this blog posting as an endorsement or promotion of the Melan-100 Light Source product. The Melan-100 Light Source information is posted here to discuss how it can be used for SARDs/IMR diagnosis.
Assuming that you are a concerned pet owner who is researching SARDs/IMR because your pet is afflicted, we’ll start this post in layman’s terms.
Diagnosing and detecting SARDs/IMR is relatively simple, but it requires having access to the right equipment. With the right equipment, your veterinarian or veterinary ophthalmologist can perform a simple Blue and Red Light test to determine if your dog has SARDs/IMR.
This test is called Colorimetric Pupil Light Reflex (PLR) Analysis. Basically, the veterinary ophthalmologist observes the behavior of the pupils when Blue and Red light is shined on them.
The equipment necessary is called a Melan-100 Light Source. It is manufactured by Biomed Vision Technologies in Ames, IA. The current retail price for these units is a mere USD $1400.
Just like thermometers, a Melan-100 unit should be present in all veterinary clinics. And just as a temperature is taken at every vet visit, a PLR test should be performed just as regularly.
While general veterinary practitioners may not be able, nor willing, to treat SARDs/IMR, they should enable themselves to early detection by owning a unit. Early detection is the best way to protect the vision, and respect the health and lives of canine patients.
Melan-100
Melan-100 Portable
The manufacturer also provides a very brief document on how the equipment can be used for diagnosis: Melan-100: How to use it.
Added on 2009.06.04 – Biomed Vision Technologies also publishes a matrix of tests that can be performed using the Melan-100 unit. You can click here for this matrix: Melan-100 Test Scenario Matrix.
Suzanne & Jay’s commentary:
If you are observing your veterinary ophthalmologist performing the PLR, please be aware of whether he/she attempts to use white light first to observe pupil constriction. Using white light prior to using the Blue / Red light has a chance of skewing the Blue and Red Light PLR.
Our own experience has been with a specialist that used white light prior to the Blue / Red light PLR. Oscar’s pupils responded to white light, as SARDs dogs’ pupils do, however, his pupils did not respond in a consistent manner for SARDs diagnosis because of the tainted observation using white light. As a result, the specialist, despite having a Melan-100 Light Source, could not diagnose confidently whether the condition was SARDs or IMR.
However, upon visiting Dr. Grozdanic at Iowa State University, the Blue and Red Light PLR was consistent with Dr. Grozdanic’s explanation of the difference between SARDs and IMR:
- SARDs — good response to Blue Light PLR; no response to Red Light PLR, as pupils remain dilated.
- IMR – good response to Blue Light PLR; some/slow response to Red Light PLR, with eventual constriction of pupils.
Please refer to the Sudden Acquired Retinal Degeneration Syndrom (SARDs) and Immune Mediated Retinitis (IMR) — approach to diagnostic and therpeutic modalities presentation on our Documentation page.
The following is an excerpt from Antibody-Mediated Retinopathies in Canine Patients: Mechanism, Diagnosis, and Treatment Modalities, written by the following:
- Sinisa D. Grozdanic, DVM, PhD
- Matthew M. Harper, PhD
- Helga Kecova, DVM, PhD
Colorimetric Pupil Light Reflex [PLR] Analysis in Diagnosis of Sudden Acquired Retinal Degeneration Syndrome
…A recent study described detailed spectral properties of the PLR response in healthy canine eyes and in the eyes of dogs that have SARDS [6]. It has been demonstrated that dogs that have SARDS have strong pupil responses when blue light of narrow wave length (480 nm) and of high light intensity (200 kcd/m2) is used, most likely as a result of stimulation of a photosensitive pigment, melanopsin [6].
Melanopsin is a vitamin A–based photosensitive pigment located in a specific subpopulation of retinal ganglion cells that can drive PLR responses even in the complete absence of photoreceptor activity, as is the case with patients that have SARDS. If red light of a specific wave length (630 nm) and high light intensity (200 kcd/m2) is used for pupil light stimulation (red light of 630-nm wave length does not overlap with the melanopsin spectral sensitivity and cannot activate melanopsin), however, the PLR response in patients with severe or complete photoreceptor dysfunction is absent [6].
This particular physiologic property of the PLR response can be effectively used to establish the fast diagnosis of SARDS. Because patients that have SARDS do not have photoreceptor activity, activation of the photoreceptor-mediated pathway (red light illumination) results in a fixed and dilated pupil, whereas activation of the melanopsin pathway (blue light illumination) results in the complete pupil constriction [6].At this time, the authors have tested nearly 200 patients that have different forms of retinal and optic nerve disease and did not notice any other form of ocular disease in canine patients with a normal retinal appearance in which such characteristic PLR properties (eg, no red response, good blue response) could be detected.
Currently, the only available instrument on the market for colorimetric PLR testing is a Melan-100 unit (BioMed Vision Technologies, Inc., Ames, Iowa). This particular unit was built to match spectral properties of canine visual pigments; it is a portable instrument and has powerful diode-based light sources with narrow wave lengths for blue and red light, which fit to spectral sensitivity curves of melanopsin (480 nm) and rod-cone opsins (630 nm).
The excerpt appears on page 363 of the Veterinary Clinics of North America (VCNA), Small Animal Practice publication, Volume 38, Number 2, March 2008.
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