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Clinical Conditions

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Ophthalmic and Neurologic Conditions

For decades, Diagnosys has assisted clinicians in early detection of many ophthalmic conditions that may cause vision loss or even blindness. We also assist clinical researchers not only in discovering new treatments such as gene therapies that may improve vision in those afflicted with inherited diseases, but also in identifying biomarkers for several psychiatric conditions.

The following list includes common ophthalmic and neurological conditions in which visual function tests may be of assistance to the clinician. Supporting scientific papers are available in our Resource Center.

Diabetic retinopathy is the most common cause of vision loss and blindness among working age-adults worldwide. Approximately 50% of people with diabetic retinopathy will over time also develop diabetic macular edema as blood vessels leak and cause swelling in the macula. Diabetic retinopathy can also lead to a form of glaucoma (neovascular glaucoma) when abnormal blood vessels grow and block fluid from draining out of the eye. While there have been improvements in diabetic management and glycemic control, diabetic retinopathy remains a major health concern due to an increasing number of people with diabetes.

Early diagnosis is key to preventing vision loss. Recent scientific research has shown that although diabetic retinopathy is staged clinically according to vascular abnormalities, the retina is predominately neural tissue and diagnosing neural retinal dysfunction may be possible during the early stages of diabetic retinopathy before vascular changes are apparent. According to ISCEV, both multifocal ERG (mfERG) and full-field ERG (flash and flicker) are objective tests that can assist in diagnosing early stage diabetic retinopathy by tracking neurodegeneration in the retina2.

Diagnosys Stimulators: ColorDome, ColorBurst, ColorFlash
Diagnosys Tests: ffERG
Additional Resources: Peer-reviewed literature, 2: ISCEV Guide 

Glaucoma is a progressive condition that damages optic nerve and retinal ganglion cells (RGC). Typical indicators include elevated intraocular pressure and abnormal cup to disc ratio prior to measurable visual field loss. After numerous studies over the past decade, evidence suggests that, in glaucoma, RGCs undergo a prolonged period of dysfunction and degeneration before any observable structural changes or cell loss. As any damage to RGCs is irreparable, early detection is essential to minimizing vision loss.

ISCEV standard tests for detecting dysfunction of RGCs include pattern ERG (PERG) and photopic negative response (PhNR).

Diagnosys Stimulators: ColorDome, ColorBurst, ColorFlash, Envoy
Diagnosys Tests: PhNR, pattern ERG
Additional Resources: Peer-reviewed literature

Inherited retinal diseases (IRDs) are a group of clinically and genetically heterogeneous diseases, which cause visual loss due to improper development or premature death of the retinal photoreceptors. IRDs affect individuals of all ages, with different IRDs progressing at different rates. Many IRDs are degenerative, getting worse over time and causing severe vision loss or even blindness.

Electrophysiology (ffERG, mfERG, PERG, PhNR, EOG) responses are objective measures of retinal function and assist in accurately differentiating between IRDs as well as judging the severity of the specific IRD2. The information from these tests can also assist with counseling and developing life management skills. In addition, ERG and the psychophysical tests (DA and FST) assist with gene therapy trials that may improve outcomes for people born with an IRD2.

Additional Resources: Peer-reviewed literature, 2: ISCEV Guide

Bestrophinopathies are a recognizable phenotype of degenerative eye diseases caused by inherited mutations in the BEST1 gene, including Best vitelliform macular dystrophy (BVMD), initially known as Best’s Disease, autosomal recessive bestrophinopathy (ARB) and autosomal dominant vitreoretinochoroidopathy (ADVIRC). BEST1 mutations may also play a role in other ophthalmic diseases like rod-cone dystrophy and early-onset cataracts.

Bestrophinopathies are characterized by abnormal ocular development, which leads to impaired function in the retinal pigment epithelium (RPE) layer resulting in yellowish sub-retinal lesions. Besides the lesions, ARB patients may have hyperopia, amblyopia, angle closure glaucoma, and short axial length. Visual acuity usually begins decreasing by age 10 and progresses slowly over time. Patients with ADVIRC will often have a 360-degree peripheral retinal circumferential hyperpigmented band, punctate white opacities in the retina, retinal neovascularization, and a breakdown of the blood-retinal barrier.

All bestrophinopathies are characterized by a decreased electrooculogram (EOG) Arden ratio (light peak/dark trough). Both full-field ERG (ffERG) and multifocal ERG (mfERG) can assist in differentiating within the phenotype as well as tracking the progression of the condition.

Congenital Achromatopsia is a hereditary vision disorder characterized by lack of cone vision due to malfunction of the retinal phototransduction pathway. The cone photoreceptors are unable to properly respond to a light stimulus. People with achromatopsia are partially or totally color blind. They also have poor visual acuity, photophobia, and pendular nystagmus. Currently, there are four known gene mutations that cause this disorder.

There are two subtypes in this condition and both types have abnormal ERG recordings with preservation of the rod-mediated ERG. Patients with the more severe subtype show nondetectable cone function in an ERG test while patients with the less severe subtype show some residual cone function. Gene therapy studies of animal models of human achromatopsia have had some success in recovering cone function.

Congenital Stationary Night Blindness (CSNB) is a clinically and genetically heterogeneous group of hereditary retinal disorders primarily affecting the photoreceptors, although the retinal pigment epithelium and the bipolar cells may also be affected. Types within this group differ in electrophysiological characteristics as well as fundus appearance and mode of inheritance. People with this condition typically have difficulty adapting to low light situations due to impaired photoreceptor transmission. They also have reduced acuity, mild to severe nearsightedness, nystagmus, and strabismus. While these vision problems are present at birth, they tend to remain stable over time.

The full-field ERG can assist diagnosing different forms of CSNB.

Leber Congenital Amaurosis (LCA) is a group of hereditary retinal diseases causing the most severe form of IRD in which both rods and cones are either nonfunctional at birth or are lost within the first years of life. It is also the most common cause of inherited blindness in children. Profound visual impairment is usually present from birth along with abnormal or absent pupillary response. People with this condition may also have photophobia, nystagmus, strabismus, and cataracts.

In addition to vision loss in infancy and sluggish pupillary response, LCA is characterized by a severely reduced or non-detectable scotopic and photopic ERG response. Recently, the US Food and Drug Association approved a gene therapy product, voretigene neparvovec-rzyl (LUXTURNA™) by Spark Therapeutics. LUXTURNA™ treats LCA caused by bi-allelic mutations in the RPE65 gene. This drug was the first US FDA approved gene therapy product for the eye. DiagnosysFST was not only used for the clinical trial but is now also used clinically for assessing vision pre and post LUXTURNA™ treatment.

Leber Hereditary Optic Neuropathy (LHON) is the most common inherited mitochondrial disorder and typically affects young males more than females. The disorder leads to degeneration of the retinal ganglion cells with painless sub acute central vision loss in one or both eyes during the young adult years. Although not classically considered an IRD because it is an optic nerve issue, LHON is still often grouped with IRDs.

A recent study has shown the PhNR amplitude is significantly decreased in people with LHON, and can distinguish carriers from controls. Treatment options are limited but include the use of antioxidant supplements. Gene therapy trials are currently underway.

Retinitis Pigmentosa (RP), also known as rod-cone degeneration, is the most common form of IRD. RP is a group of eye disorders that causes progressive vision loss as the rod photoreceptors degenerate in the early stages of the disease, followed by cone cell death. Symptoms include trouble seeing at night, decreased peripheral vision often leading to tunnel vision, and possibly even blindness. RP generally presents as night blindness in adolescence with ensuing visual field loss from early adulthood.

Full-field electroretinograms (ffERGs) assist in the diagnosis of widespread forms of retinitis pigmentosa in early life, even before fundus abnormalities visible with an ophthalmoscope are detectable. Dark adaptometry (DA) may also be useful in detecting early cases because in RP dark adaptation is usually prolonged2.

Stargardt Disease is the most common form of inherited macular degeneration. The progressive vision loss is caused by degeneration of photoreceptor cells in the macula (cones, then rods) due to abnormal accumulation of fatty yellow clumps called lipofuscin. People with Stargardt disease may also have problems with night vision and possibly with color vision. The signs and symptoms of Stargardt disease typically appear in late childhood to early adulthood and worsen over time. It is most commonly caused by mutations in the ABCA4 gene.

While there is currently no cure, research is ongoing to help minimize vision loss due to this condition. This research also includes gene therapy trials. Electroretinograms (ERGs) provide useful information to assist in counseling and life management skills. Additionally, ERGs and psychophysical tests are being used in clinical trials.

Usher Syndrome is the most common inherited condition that causes combined progressive hearing and vision loss. Vision loss is due to retinitis pigmentosa (RP) while hearing loss is due to abnormalities within the inner ear. Newborns often have moderate to severe hearing impairment while symptoms of RP start shortly after adolescence.

Retinitis Pigmentosa (RP), also known as rod-cone degeneration, is the most common form of IRD. RP is a group of eye disorders that causes progressive vision loss as the rod photoreceptors degenerate in the early stages of the disease, followed by cone cell death. Symptoms include trouble seeing at night, decreased peripheral vision often leading to tunnel vision, and possibly even blindness. RP generally presents as night blindness in adolescence with ensuing visual field loss from early adulthood.

Full-field electroretinograms (ffERGs) assist in the diagnosis of widespread forms of retinitis pigmentosa in early life, even before fundus abnormalities visible with an ophthalmoscope are detectable. Dark adaptometry (DA) may also be useful in detecting early cases because in RP dark adaptation is usually prolonged.

X-linked Retinoschisis (XLRS) is an inherited disease caused by mutations in the Retinoschisin 1 gene that causes loss of central and peripheral vision characterized by abnormal splitting within the inner retinal layers. Patients may also have nystagmus, strabismus, hyperopia, foveal ectopia, hemorrhage, or retinal detachment. It is the leading cause of macular degeneration in males. Vision loss happens between 10 and 20 years of age.

The full-field ERG (ffERG) can be useful in diagnosis of XLRS because under dark adapted conditions, the b-wave amplitude can be disproportionately reduced with a preserved a-wave. This electronegative response is a common feature among XLRS patients. A recent study has discovered an abnormal pupil response in XLRS patients when tested with low to moderate flash luminance levels. In addition, the full field stimulus threshold (FST) is normal or nearly normal in XLRS. The use of multiple functional tests provides insight into the different aspects of XLRS abnormality and may be of use in future clinical trials.

There are several neurological conditions that may affect the visual pathway from the optic nerve head to the visual cortex resulting in vision loss or even blindness. These conditions include autism, bipolar disorder, brain tumors, idiopathic intracranial hypertension, multiple sclerosis, NOVL optic neuritis, optic neuropathy, schizophrenia, and traumatic brain injury.

Electroretinograms (ERG) and visual evoked potentials (VEP) are useful in clinical diagnosis as well as evaluating the severity of optic neurological conditions. ERGs are used to evaluate retinal function while VEPs enable objective determination of deficiencies along the entire visual pathway. VEPs may even help grade the severity of cortical dysfunction as VEP amplitude can detect axonal damage in the optic nerve, whereas VEP latency is associated with the extent of myelination. VEPs have diverse applications from monitoring visual pathway maturation in infants with poor vision or amblyopia to monitoring optic nerve function in patients with known neurological diseases. In addition, ongoing research has shown that ERGs may contribute to helping diagnose psychiatric conditions by measuring the function of certain biomarkers.

Additional Resources: Peer-reviewed literature

Autism, also known as autism spectrum disorder (ASD) is a complicated condition that is characterized by impairments in language, imagination, and social interaction. ASD ranges from being a minor problem to a disability that needs full-time care in a special facility.

Because the retina is mostly neural tissue, ERGs can function as an objective biomarker in certain psychiatric conditions. Researchers have reported low ERG b-wave amplitudes and atypical cone bipolar synaptic function in ASD individuals. A larger study of the ERG in ASD individuals and their relatives is necessary to solidify the clinical utility of ERG as a clinical measure of central nervous system function in this neurodevelopmental disorder.

Brain Tumors: Tumors, even benign ones, can damage the optic nerve causing vision changes such as blurriness or cloudiness, which then can lead to vision loss and blindness. Meningiomas, the most frequently reported intracranial neoplasm, can occur in the orbit, optic canal, or intracranial area and will typically cause vision loss over months or years. Optic nerve glioma (ONG) is a specific type of brain tumor found in the optic chiasm and is often associated with the genetic condition neurofibromatosis 1 (NF1). ONGs due to NF1 appear in young children and are often benign, however some ONGs will be aggressive and cause significant vision loss.

Research has shown that pattern ERG and pattern VEP can be used to locate the position of tumors when they are in the retina, the optic nerve, the chiasm, or the post chiasmal pathways. Early recognition of optic nerve compression is vital for minimizing vision loss.

Idiopathic Intracranial Hypertension (IIH) is a condition of elevated intracranial pressure (ICP) in individuals who have signs and symptoms of increased ICP but no structural abnormalities other then those associated with increased ICP or cerebrospinal fluid. When pressure around the brain is too high it can put pressure on the optic nerve and disc, causing swelling that could potentially lead to damage and vision loss.

Individuals with IIH may experience dim, blurry, or dull vision. Their vision may completely disappear for short periods of time. Double vision may also happen if they stoop down or bend over. Both the pattern ERG (PERG) and the PhNR are useful in determining any retinal ganglion cell dysfunction in IIH individuals.

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