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Oguchi disease present with nonprogressive night blindness since young childhood or birth with normal day vision, but they frequently claim improvement of light sensitivities when they remain for some time in a darkened environment.
On examination patients have normal visual fields but the fundos have a diffuse or patchy, silver-gray or golden-yellow metallic sheen and the retinal vessels stand out in relief against the background.
A prolonged dark adaptation of three hours or more, leads to disappearance of this unusual discoloration and the appearance of a normal reddish appearance. This is known as the Mizuo-Nakamura phenomena and is thought to be caused by the overstimulation of rod cells.
Other conditions with similar appearing fundi include
- Cone dystrophy
- X-linked retinitis pigmentosa
- Juvenile macular dystrophy
These conditions do not show the Mizuo-Nakamura phenomenon.
The first symptom of this disease is usually a slow loss of vision. Early signs of Retinitis include loss of night vision; making it harder to drive at night. Later signs of retinitis include loss of peripheral vision, leading to tunnel vision. In some cases, symptoms are experienced in only one of the eyes. Experiencing the vision of floaters, flashes, blurred vision and loss of side vision in just one of the eyes is an early indication of the onset of Retinitis.
The initial retinal degenerative symptoms of retinitis pigmentosa are characterized by decreased night vision (nyctalopia) and the loss of the mid-peripheral visual field. The rod photoreceptor cells, which are responsible for low-light vision and are orientated in the retinal periphery, are the retinal processes affected first during non-syndromic forms of this disease. Visual decline progresses relatively quickly to the far peripheral field, eventually extending into the central visual field as tunnel vision increases. Visual acuity and color vision can become compromised due to accompanying abnormalities in the cone photoreceptor cells, which are responsible for color vision, visual acuity, and sight in the central visual field. The progression of disease symptoms occurs in a symmetrical manner, with both the left and right eyes experiencing symptoms at a similar rate.
A variety of indirect symptoms characterize retinitis pigmentosa along with the direct effects of the initial rod photoreceptor degeneration and later cone photoreceptor decline. Phenomena such as photophobia, which describes the event in which light is perceived as an intense glare, and photopsia, the presence of blinking or shimmering lights within the visual field, often manifest during the later stages of RP. Findings related to RP have often been characterized in the fundus of the eye as the "ophthalamic triad". This includes the development of (1) a mottled appearance of the retinal pigment epithelium (RPE) caused by bone spicule formation, (2) a waxy appearance of the optic nerve, and (3) the attentuation of blood vessels in the retina.
Non-syndromic RP usually presents a variety of the following symptoms:
- Night blindness
- Tunnel vision (due to loss of peripheral vision)
- Latticework vision
- Photopsia (blinking/shimmering lights)
- Photophobia (aversion to glare)
- Development of bone spicules in the fundus
- Slow adjustment from dark to light environments and vice versa
- Blurring of vision
- Poor color separation
- Loss of central vision
- Eventual blindness
Since the "CHM" gene is located on the X chromosome, symptoms are seen almost exclusively in men. While there are a few exceptions, female carriers have a noticeable lack of pigmentation in the RPE but do not experience any symptoms. Female carriers have a 50% chance of having either an affected son or a carrier daughter, while a male with choroideremia will have all carrier daughters and unaffected sons.
Even though the disease progression can vary significantly, there are general trends. The first symptom many individuals with choroideremia notice is a significant loss of night vision, which begins in youth. Peripheral vision loss occurs gradually, starting as a ring of vision loss, and continuing on to "tunnel vision" in adulthood. Individuals with choroideremia tend to maintain good visual acuity into their 40s, but eventual lose all sight at some point in the 50-70 age range. A study of 115 individuals with choroideremia found that 84% of patients under the age of 60 had a visual acuity of 20/40 or better, while 33% of patients over 60 years old had a visual acuity of 20/200 or worse. The most severe visual acuity impairment (only being able to count fingers or worse) did not occur until the seventh decade of life. The same study found the rate of visual acuity loss to be about 1 eye chart row per 5 years.
The term congenital refers to a condition present from birth (not acquired) and amaurosis refers to a loss of vision "not" associated with a lesion. However, beyond these general descriptions, the presentation of LCA can vary, because it is associated with multiple genes.
LCA is typically characterized by nystagmus, sluggish or absent pupillary responses, and severe vision loss or blindness.
There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy.
RP may be:
(1) Non-syndromic, that is, it occurs alone, without any other clinical findings,
(2) Syndromic, with other neurosensory disorders, developmental abnormalities, or complex clinical findings, or
(3) Secondary to other systemic diseases.
- RP combined with deafness (congenital or progressive) is called Usher syndrome.
- Alport's syndrome is associated with RP and an abnormal glomerular-basement membrane leading nephrotic syndrome and inherited as X-linked dominant.
- RP combined with ophthalmoplegia, dysphagia, ataxia, and cardiac conduction defects is seen in the mitochondrial DNA disorder Kearns-Sayre syndrome (also known as Ragged Red Fiber Myopathy)
- RP combined with retardation, peripheral neuropathy, acanthotic (spiked) RBCs, ataxia, steatorrhea, is absence of VLDL is seen in abetalipoproteinemia.
- RP is seen clinically in association with several other rare genetic disorders (including muscular dystrophy and chronic granulomatous disease) as part of McLeod syndrome. This is an X-linked recessive phenotype characterized by a complete absence of XK cell surface proteins, and therefore markedly reduced expression of all Kell red blood cell antigens. For transfusion purposes these patients are considered completely incompatible with all normal and K0/K0 donors.
- RP associated with hypogonadism, and developmental delay with an autosomal recessive inheritance pattern is seen with Bardet-Biedl syndrome
Other conditions include neurosyphilis, toxoplasmosis and Refsum's disease.
Symptoms of BCD include:
- Crystals in the cornea (the clear covering of the eye)
- Yellow, shiny deposits on the retina
- Progressive atrophy of the retina, choriocapillaries and choroid (the back layers of the eye). This tends to lead to progressive night blindness and visual field constriction.
In general, PRAs are characterised by initial loss of rod photoreceptor cell function followed by that of the cones and for this reason night blindness is the first significant clinical sign for most dogs affected with PRA. As other retinal disorders, PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then degenerate during the dog's lifetime.
Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).
Choroideremia (; CHM) is a rare, X-linked recessive form of hereditary retinal degeneration that affects roughly 1 in 50,000 males. The disease causes a gradual loss of vision, starting with childhood night blindness, followed by peripheral vision loss, and progressing to loss of central vision later in life. Progression continues throughout the individual's life, but both the rate of change and the degree of visual loss are variable among those affected, even within the same family.
Choroideremia is caused by a loss-of-function mutation in the "CHM" gene which encodes Rab escort protein 1 (REP1), a protein involved in lipid modification of Rab proteins. While the complete mechanism of disease is not fully understood, the lack of a functional protein in the retina results in cell death and the gradual deterioration of the choroid, retinal pigment epithelium (RPE), and retinal photoreceptor cells.
As of 2017, there is no treatment for choroideremia; however, retinal gene therapy clinical trials have demonstrated a possible treatment.
The X-linked varieties of congenital stationary night blindness (CSNB) can be differentiated from the autosomal forms by the presence of myopia, which is typically absent in the autosomal forms. Patients with CSNB often have impaired night vision, myopia, reduced visual acuity, strabismus, and nystagmus. Individuals with the complete form of CSNB (CSNB1) have highly impaired rod sensitivity (reduced ~300x) as well as cone dysfunction. Patients with the incomplete form can present with either myopia or hyperopia.
Leber's congenital amaurosis (LCA) is a rare inherited eye disease that appears at birth or in the first few months of life.
One form of LCA was successfully treated with gene therapy in 2008.
It affects about 1 in 40,000 newborns. LCA was first described by Theodor Leber in the 19th century. It should not be confused with Leber's hereditary optic neuropathy, which is a different disease also described by Theodor Leber.
Retinitis is inflammation of the retina in the eye, which can permanently damage the retina and lead to blindness. The retina is the part of your eye that is also known as the "sensing tissue." Retinitis may be caused by a number of different infectious agents. Retinitis, also called Retinitis pigmentosa, has a prevalence of one in every 2,500-7,00 people. This condition is one of the leading causes that leads to blindness in patients in the age range of 20-60 years old.
Retinitis may be caused by several infectious agents, including toxoplasmosis, cytomegalovirus and candida. Cytomegalovirus retinitis is an important cause of blindness in AIDS patients, and is the most common cause of vision loss in AIDS patients. Candida may spread to the retina from the bloodstream, which usually leads to the production of several abscesses in the retina.
Aside from a complete inability to see color, individuals with complete achromatopsia have a number of other ophthalmologic aberrations. Included among these aberrations are greatly decreased visual acuity (<0.1 or 20/200) in daylight, Hemeralopia, nystagmus, and severe photophobia. The fundus of the eye appears completely normal. Also see Pingelap.
In general, symptoms of incomplete achromatopsia are similar to those of complete achromatopsia except in a diminished form. Individuals with incomplete achromatopsia have reduced visual acuity with or without nystagmus or photophobia. Furthermore, these individuals show only partial impairment of cone cell function but again have retained rod cell function.
Nyctalopia (from Greek νύκτ-, "nykt-" "night"; ἀλαός, "alaos" "blind, not seeing", and ὄψ, "ops" "eye"), also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition (for example, vitamin A deficiency). It can be described as insufficient adaptation to darkness.
The most common cause of nyctalopia is retinitis pigmentosa, a disorder in which the rod cells in the retina gradually lose their ability to respond to the light. Patients suffering from this genetic condition have progressive nyctalopia and eventually their daytime vision may also be affected. In X-linked congenital stationary night blindness, from birth the rods either do not work at all, or work very little, but the condition doesn't get worse.
Another cause of night blindness is a deficiency of retinol, or vitamin A, found in fish oils, liver and dairy products.
The opposite problem, the inability to see in bright light, is known as "hemeralopia" and is much rarer.
Since the outer area of the retina is made up of more rods than cones, loss of peripheral vision often results in night blindness. Individuals suffering from night blindness not only see poorly at night, but also require extra time for their eyes to adjust from brightly lit areas to dim ones. Contrast vision may also be greatly reduced.
Rods contain a receptor-protein called rhodopsin. When light falls on rhodopsin, it undergoes a series of conformational changes ultimately generating electrical signals which are carried to the brain via the optic nerve. In the absence of light, rhodopsin is regenerated. The body synthesizes rhodopsin from vitamin A, which is why a deficiency in vitamin A causes poor night vision.
Refractive "vision correction" surgery (especially PRK with the complication of "haze") may rarely cause a reduction in best night-time acuity due to the impairment of contrast sensitivity function (CSF) which is induced by intraocular light-scatter resulting from surgical intervention in the natural structural integrity of the cornea.
X-linked congenital stationary night blindness (CSNB) is a rare X-linked non-progressive retinal disorder. It has two forms, complete, also known as type-1 (CSNB1), and incomplete, also known as type-2 (CSNB2), depending on severity. In the complete form (CSNB1), there is no measurable rod cell response to light, whereas this response is measurable in the incomplete form. Patients with this disorder have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients also often have reduced visual acuity, myopia, nystagmus, and strabismus. CSNB1 is caused by mutations in the gene NYX, which encodes a protein involved in retinal synapse formation or synaptic transmission. CSNB2 is caused by mutations in the gene CACNA1F, which encodes a voltage-gated calcium channel Ca1.4.
Not all Congenital Stationary Night Blindness (CSNB) are inherited in X-linked pattern. There are also dominant and recessive inheritance patterns for CSNB.
The most common sign at presentation is leukocoria (abnormal white reflection of the retina). Symptoms typically begin as blurred vision, usually pronounced when one eye is closed (due to the unilateral nature of the disease). Often the unaffected eye will compensate for the loss of vision in the other eye; however, this results in some loss of depth perception and parallax. Deterioration of sight may begin in either the central or peripheral vision. Deterioration is likely to begin in the upper part of the vision field as this corresponds with the bottom of the eye where blood usually pools. Flashes of light, known as photopsia, and floaters are common symptoms. Persistent color patterns may also be perceived in the affected eye. Initially, these may be mistaken for psychological hallucinations, but are actually the result of both retinal detachment and foreign fluids mechanically interacting with the photoreceptors located on the retina.
One early warning sign of Coats' disease is yellow-eye in flash photography. Just as the red-eye effect is caused by a reflection off blood vessels in the back of a normal eye, an eye affected by Coats' will glow yellow in photographs as light reflects off cholesterol deposits. Children with yellow-eye in photographs are typically advised to immediately seek evaluation from an optometrist or ophthalmologist, who will assess and diagnose the condition and refer to a vitreo-retinal specialist.
Coats' disease itself is painless. Pain may occur if fluid is unable to drain from the eye properly, causing the internal pressure to swell, resulting in painful glaucoma.
Bietti's crystalline dystrophy (BCD), also called Bietti crystalline corneoretinal dystrophy, is a rare autosomal recessive eye disease named after Dr. G. B. Bietti.
BCD is a rare disease and appears to be more common in people with Asian ancestry.
Hemeralopia (from Greek "ημέρα", hemera "day"; and "αλαός", alaos "blindness") is the inability to see clearly in bright light and is the exact opposite of nyctalopia (night blindness). Hemera was the Greek goddess of day and Nyx was the goddess of night. However, it has been used in an opposite sense by many non-English-speaking doctors. It can be described as insufficient adaptation to bright light. It is also called heliophobia and day blindness.
In hemeralopia, daytime vision gets worse, characterised by photoaversion (dislike/avoidance of light) rather than photophobia (eye discomfort/pain in light) which is typical of inflammations of eye. Nighttime vision largely remains unchanged due to the use of rods as opposed to cones (during the day), which are affected by hemeralopia and in turn degrade the daytime optical response. Hence many patients feel they see better at dusk than in daytime.
Quite often, the presenting symptom of ornithine aminotransferase (OAT) deficiency is myopia which progresses to night blindness. The onset of myopia is often in early childhood. Ophthalmological findings in affected individuals include constricted visual fields, posterior subcapsular cataracts (can begin in late teens), elevated dark adaptation thresholds and decreased or absent electroretinographic responses. Symptoms of OAT deficiency are progressive, and between the ages of 45 and 65, most affected individuals are almost completely blind.
In some cases, affected individuals will present in the neonatal period with disease that closely mimics a classic urea cycle defect, such as ornithine transcarbamylase deficiency, as the block in ornithine metabolism leads to secondary dysfunction of the urea cycle. These individuals present with hyperammonemia, poor feeding, failure to thrive and increased excretion of orotic acid.
Coats' disease, (also known as exudative retinitis or retinal telangiectasis, sometimes spelled Coates' disease), is a rare congenital, nonhereditary eye disorder, causing full or partial blindness, characterized by abnormal development of blood vessels behind the retina. Coats' disease can also fall under glaucoma.
It can have a similar presentation to that of retinoblastoma.
Hemeralopia is known to occur in several ocular conditions. Cone dystrophy and achromatopsia, affecting the cones in the retina, and the anti-epileptic drug Trimethadione are typical causes. Adie's pupil which fails to constrict in response to light; Aniridia, which is absence of the iris; Albinism where the iris is defectively pigmented may also cause this. Central Cataracts, due to the lens clouding, disperses the light before it can reach the retina, is a common cause of hemeralopia and photoaversion in elderly. C.A.R (Cancer Associated Retinopathy) seen when certain cancers incite the production of deleterious antibodies against retinal components, may cause hemeralopia.
Another known cause is a rare genetic condition called Cohen Syndrome (aka Pepper Syndrome). Cohen syndrome is mostly characterized by obesity, mental retardation, and craniofacial dysmorphism due to genetic mutation at locus 8q22-23. Rarely it may have ocular complications such as hemeralopia, pigmentary chorioretinitis, optic atrophy or retinal/iris coloboma, having a serious effect on the person's vision.
Yet another cause of hemeralopia is uni- or bilateral postchiasmatic brain injury. This may also cause concomitant night blindness.
Autosomal dominant optic atrophy can present clinically as an isolated bilateral optic neuropathy (non-syndromic form) or rather as a complicated phenotype with extra-ocular signs (syndromic form).
Dominant optic atrophy usually affects both eyes roughly symmetrically in a slowly progressive pattern of vision loss beginning in childhood and is hence a contributor to childhood blindness. Vision testing will reveal scotomas (areas of impaired visual acuity) in the central visual fields with peripheral vision sparing and impaired color vision (color blindness). Visual acuity loss varies from mild to severe, typically ranging from 6/6 (in meters, equivalent to 20/20, ft) to 6/60 (20/200, ft) with a median value of 6/36 (roughly equivalent to 20/125 ft), corrected vision. In rare cases, vision loss is more severe.
Characteristic changes of the fundus evident on examination is temporal pallor (indicating atrophy) of the optic disc and in its end stage, excavation of the optic disc, as is also seen in Leber hereditary optic neuropathy and normal tension glaucoma.
Because the onset of Dominant optic atrophy is insidious, symptoms are often not noticed by the patients in its early stages and are picked up by chance in routine school eye screenings. First signs of Kjer's typically present between 4–6 years of age, though presentation at as early as 1 year of age has been reported. In some cases, Dominant optic atrophy may remain subclinical until early adulthood.
Progression of dominant optic atrophy varies even within the same family. Some have mild cases with visual acuity stabilizing in adolescence, others have slowly but constantly progressing cases, and others still have sudden step-like decreases in visual acuity. Generally, the severity of the condition by adolescence reflects the overall level of visual function to be expected throughout most of the patient’s adult life (Votruba, 1998). Slow decline in acuity is known to occur in late middle age in some families.
In complicated cases of autosomal dominant optic atrophy, in addition to bilateral optic neuropathy, several other neurological signs of neurological involvement can be observed: peripheral neuropathy, deafness, cerebellar ataxia, spastic paraparesis, myopathy.