Sudden acquired retinal degeneration
Encyclopedia
Sudden acquired retinal degeneration syndrome (SARDS) is a disease in dogs causing sudden blindness. It can occur in any breed, but female dogs may be predisposed. Approximately 4000 cases are seen in the United States
annually.
The cause of SARDS is considered to be idiopathic
and the veterinary community is divided as to its cause, but the disease possibly involves autoimmune disease
, toxins, elevations in adrenal sex hormones or Cushing's disease
.
Symptoms include sudden permanent blindness, but may occur more slowly over several days, weeks or months, dilated pupil
s, and loss of the pupillary light reflex
. Other symptoms commonly seen are similar to those seen with Cushing's disease and include increased water consumption and urination, weight gain, confusion, restlessness, behavioral changes and lethargy. These symptoms may develop over a few months preceding the onset of SARD. Despite similar symptoms and blood test results to Cushing's disease, evaluation of dogs with SARD did not reveal any tumors in the pituitary
or adrenal gland
s. However, endocrine testing (i.e., Canine Adrenal Panel at the University of Tennessee College of Veterinary Medicine Endocrinology Service) often shows elevations in adrenal sex hormones. Clinical signs and disease progression vary markedly among individual animals, depending on the number and type of hormones that are increased, the degree of hormone elevation, and the age of the dog. Autoimmune disease as a cause has also been called into question because of a lack of antiretinal autoantibodies
in dogs with SARD in one study.
Examination with an ophthalmoscope will initially show no changes, but in a few months atrophy
of the retina
will resemble the appearance of progressive retinal atrophy
. Pathologically
, there is a loss of the rod
and cone cell
s followed by degeneration of other layers of the retina. The retinal degeneration appears to be related to apoptosis
of these cells. SARD must be distinguished from other causes of sudden blindness that have no visible pathology, including retrobulbar optic neuritis
, a tumor at the optic chiasm
, or other central nervous system
diseases. Electroretinography
is useful to definitively diagnose SARD. Currently there is no approved treatment, although the use of intravenous immunoglobulin
has been investigated due to similarities between SARD and human immune-mediated retinopathy
.
Endocrine testing by National Veterinary Diagnostic Services (the only laboratory that offers the endocrine-immune blood test developed by Alfred Plechner, DVM) revealed that some pets with SARDS had endocrine-immune abnormalities and physiological doses of cortisone and thyroid hormone were anecdotally shown to be beneficial to their overall health and vision. "Adrenal exhaustion" is a syndrome put forth by Ms. C. Levin, a lay person, who subscribes to the theories of Dr. Plechner. However, "adrenal exhaustion" (not to be confused with Addison's disease) is not recognized as a legitimate medical disorder in veterinary medicine and the condition has not been described in dogs (or cats). Moreover, this experimental hormone replacement therapy has not been approved or evaluated for efficacy and safety by the veterinary community, nor has it undergone scientific peer review in the mainstream veterinary literature.
There is also a change in eye colour when photographed, from red to green.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
annually.
The cause of SARDS is considered to be idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...
and the veterinary community is divided as to its cause, but the disease possibly involves autoimmune disease
Autoimmune disease
Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. In other words, the body actually attacks its own cells. The immune system mistakes some part of the body as a pathogen and attacks it. This may be restricted to...
, toxins, elevations in adrenal sex hormones or Cushing's disease
Cushing's syndrome
Cushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone or CRH...
.
Symptoms include sudden permanent blindness, but may occur more slowly over several days, weeks or months, dilated pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s, and loss of the pupillary light reflex
Pupillary reflex
The pupillary light reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retina of the eye, thereby assisting in adaptation to various levels of darkness and light, in addition to retinal sensitivity...
. Other symptoms commonly seen are similar to those seen with Cushing's disease and include increased water consumption and urination, weight gain, confusion, restlessness, behavioral changes and lethargy. These symptoms may develop over a few months preceding the onset of SARD. Despite similar symptoms and blood test results to Cushing's disease, evaluation of dogs with SARD did not reveal any tumors in the pituitary
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
or adrenal gland
Adrenal gland
In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
s. However, endocrine testing (i.e., Canine Adrenal Panel at the University of Tennessee College of Veterinary Medicine Endocrinology Service) often shows elevations in adrenal sex hormones. Clinical signs and disease progression vary markedly among individual animals, depending on the number and type of hormones that are increased, the degree of hormone elevation, and the age of the dog. Autoimmune disease as a cause has also been called into question because of a lack of antiretinal autoantibodies
Autoantibody
An autoantibody is an antibody manufactured by the immune system that is directed against one or more of the individual's own proteins. It is derived from the Greek "auto" which means "self", "anti" which means "against" and "body"...
in dogs with SARD in one study.
Examination with an ophthalmoscope will initially show no changes, but in a few months atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
will resemble the appearance of progressive retinal atrophy
Progressive retinal atrophy
Progressive retinal atrophy is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. Similar to retinitis pigmentosa in humans, it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness...
. Pathologically
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
, there is a loss of the rod
Rod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
and cone cell
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
s followed by degeneration of other layers of the retina. The retinal degeneration appears to be related to apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
of these cells. SARD must be distinguished from other causes of sudden blindness that have no visible pathology, including retrobulbar optic neuritis
Optic neuritis
Optic neuritis is the inflammation of the optic nerve that may cause a complete or partial loss of vision.-Causes:The optic nerve comprises axons that emerge from the retina of the eye and carry visual information to the primary visual nuclei, most of which is relayed to the occipital cortex of the...
, a tumor at the optic chiasm
Optic chiasm
The optic chiasm or optic chiasma is the part of the brain where the optic nerves partially cross...
, or other central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
diseases. Electroretinography
Electroretinography
Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors , inner retinal cells , and the ganglion cells. Electrodes are usually placed on the cornea and the skin near the eye, although it is possible to record the ERG from skin electrodes...
is useful to definitively diagnose SARD. Currently there is no approved treatment, although the use of intravenous immunoglobulin
Intravenous immunoglobulin
Intravenous immunoglobulin is a blood product administered intravenously. It contains the pooled IgG extracted from the plasma of over one thousand blood donors. IVIG's effects last between 2 weeks and 3 months...
has been investigated due to similarities between SARD and human immune-mediated retinopathy
Retinopathy
Retinopathy is a general term that refers to some form of non-inflammatory damage to the retina of the eye. Frequently, retinopathy is an ocular manifestation of systemic disease.-Pathophysiology:Causes of retinopathy are varied:...
.
Endocrine testing by National Veterinary Diagnostic Services (the only laboratory that offers the endocrine-immune blood test developed by Alfred Plechner, DVM) revealed that some pets with SARDS had endocrine-immune abnormalities and physiological doses of cortisone and thyroid hormone were anecdotally shown to be beneficial to their overall health and vision. "Adrenal exhaustion" is a syndrome put forth by Ms. C. Levin, a lay person, who subscribes to the theories of Dr. Plechner. However, "adrenal exhaustion" (not to be confused with Addison's disease) is not recognized as a legitimate medical disorder in veterinary medicine and the condition has not been described in dogs (or cats). Moreover, this experimental hormone replacement therapy has not been approved or evaluated for efficacy and safety by the veterinary community, nor has it undergone scientific peer review in the mainstream veterinary literature.
There is also a change in eye colour when photographed, from red to green.