Does Everyone With Retinitis Pigmentosa Go Blind

Does Everyone With Retinitis Pigmentosa Go Blind
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Does Everyone With Retinitis Pigmentosa Go Blind/Retinitis pigmentosa (RP) is a class of diseases involving progressive degeneration of the retina, typically starting in the mid-periphery and advancing toward the macula and fovea. Typical symptoms include night blindness followed by decreasing visual fields, leading to tunnel vision and eventually legal blindness or, in many cases, complete blindness []. On the cellular level, this correlates with a predominantly affected rod photoreceptor system. In later stages, the disease may further affect the cone photoreceptor eventually causing complete blindness. The diseased photoreceptors undergo apoptosis [], which is reflected in reduced outer nuclear layer thickness within the retina, as well as in lesions and/or retinal pigment deposits in the fundus. Patients may lose a significant portion of their photoreceptors before experiencing loss of visual acuity.

Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision.[rx] Symptoms include trouble seeing at nightand decreased peripheral vision (side vision).[rx] Onset of symptoms is generally gradual.[rx] As peripheral vision worsens, people may experience “tunnel vision”.[rx] Complete blindness is uncommon.[rx]

Does Everyone With Retinitis Pigmentosa Go Blind

Types of Retinitis Pigmentosa

The three patterns of inheritance linked to RP include:

  • Autosomal recessive – both parents are healthy but carry the gene, so each of their children has a 50 per cent chance of inheriting one gene and being a carrier, and a 25 per cent chance of inheriting both genes and developing RP.
  • Autosomal recessive – this inheritance pattern is the most common type of RP. The chance of having this condition is higher if the parents are related (for example, cousins).
  • Autosomal dominant – in this form of RP, only one parent has the gene, and is usually affected by the disease as well. Each child has a 50 per cent chance of inheriting this gene and developing RP.
  • X-linked recessive – this is a rarer type of RP. The defective gene is carried by the (usually healthy) mother and is passed to sons only via the X chromosome. Each son has a 50 per cent chance of developing RP. Each affected male patient will transmit the gene to the next generation, but only to his daughters, who will be healthy carriers.

Causes of Retinitis Pigmentosa

Night blindness in non degenerative diseases

In these cases, in contrast to RP, the disease is not evolving with time.

  • Congenital stationary night blindness – In autosomal forms, symptoms are limited to night blindness, while X-linked forms are associated with a limited visual acuity.
  • Fundus albipunctatus – is a rare condition in which fine, white deposits are visible in fundus. The fundus aspect is similar to retinitis punctata albescens (see above), but there is usually no signs of degeneration (narrowing of retinal vessels, retinal atrophy), although some cases may undergo macular degeneration [].
  • Vitamin A deprivation syndrome – mimics the signs of RP with night blindness and is associated with keratitis. If vitamin A supplementation is given early, the symptoms disappear but after a certain point the lesions become irreversible.

Non evolving pigmentary retinopathies

The aspect of the fundus is often that of salt-and-pepper pigmentary retinopathy or deposits of pigment with various shape, often dot-like.

  • Congenital infections – like rubella (salt-and-pepper retinopathy) or syphilis (pseudo-retinitis pigmentosa or leopard skin retinopathy).
  • Carriers of X-linked disorders like choroideremia – ocular albinism, RP. This helps to recognize carriers, in particular for RP in which a yellowish reflex may be present in fundus.
  • Mitochondrial diseases – like Kearns-Sayre syndrome (ophthalmoplegia), although there may be progressive degeneration of photoreceptors.
  • Grouped congenital hypertrophy – of the retinal pigment epithelium with characteristic bear-like footprints in fundus.

Choroidal dystrophies

In all cases there is a marked atrophy of the choriocapillaris that is readily diagnosed by the absence of fluorescence in fluorescein angiography.

  • Choroideremia – an X-linked disorder, due to mutations in CHM encoding the Rab Escort Protein 1 (REP1) and accounting for about 2% of pigmentary retinopathies.
  • Gyrate atrophy – a very rare autosomal recessive disorder, due to deficiency in ornithine aminotransferase.

Vitreoretinopathies

In these conditions, the vitreous and inner layers of the retina are also affected. Retinal detachment and retinal vasculopathy are often present.

  • Retinoschisis – in most cases the juvenile X-linked retinoschisis with typical spoke-wheel-like lesions in the fovea, is due to mutations in XLRS1 encoding a protein involved in the adhesion of retinal cells. End stage X-linked retinoschisis are difficult to distinguish from RP because of the macular degeneration and frequent pigmented lesions in peripheral retina. There is also the autosomal recessive Goldman Favre syndrome in which patients have night blindness from infancy and show foveal retinoschisis in fundus. It is the same disease as the Enhanced S-Cone Syndrome (ESCS) due to mutations in NR2E3, that presents with characteristic whitish and secondarily round pigmented lesions in retinal periphery when evolved.
  • Hereditary vitreoretinopathies – the most frequent ones being several autosomal dominant conditions: familial exudative vitreoretinopathy, Wagner disease and Stickler syndrome.
  • Inflammatory diseases of the eye – birdshot choroidoretinopathy, serpiginous retinopathy, multifocal placoid pigment epitheliopathy, sarcoidosis. The presentation and fundus are clearly different from RP but there may be a secondary degeneration mimicking RP.

Maculopathies

Large, extended maculopathies may be difficult to differentiate from end stage RP.

  • Stargardt disease – due to mutations in ABCA4. Null mutations in this gene can also be responsible for authentic RP.
  • Cone dystrophies – in some cases presenting with a minimal rod involvement.
  • Sorsby’s disease – in extended cases.

Secondary pigmentary changes

Several diseases may lead to secondary RP with variable disease course.

  • Intoxication – with various drugs including thioridazine and chloroquine. Although chloroquine usually leads to “bull’s eye maculopathy”, there are some cases of RP-like pigmentary retinopathies that may continue to progress even after discontinuation of the drug intake.
  • Inflammation – (pars planitis, Behcet disease, sarcoidosis, subacute diffuse unilateral neuroretinitis) may rarely be complicated with RP.
  • Sequelae of severe gravidic toxemia – uveal effusion syndrome or trauma.
  • Parasitic infections – such as onchocercosis.
  • RP combined with deafness – (congenital or progressive) is called Usher syndrome.[rx]
  • Alport’s syndrome – is associated with RP and an abnormal glomerular-basement membrane leading to nephrotic syndrome. It is 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, and absence of VLDL is seen in abetalipoproteinemia.[rx]
  • 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[rx]
  • Other conditions include neurosyphilis –  toxoplasmosis and Refsum’s disease.

Symptoms of Retinitis Pigmentosa

Does Everyone With Retinitis Pigmentosa Go Blind

  • Loss of night vision – Night blindness is when you cannot see anything in the dark. Your vision may be normal during the day. As you start losing night vision, it takes longer to adjust to darkness. You may stumble over objects or have trouble driving at dusk and at night. You might also find it hard to see in movie theaters or other dim rooms.
  • Gradual loss of peripheral (side) vision – This is known as “tunnel vision.” You may find you bump into things as you move around. This is because you are not able to see objects below and around you.
  • Loss of central vision – Some people also have problems with central vision. This can make it hard to do detailed tasks such as reading or threading a needle.
  • Problems with color vision – Some people may also have trouble seeing different colors.
  • Usher syndrome – is the most frequent syndromic form in which typical RP is associated with neurosensory deafness. About 14% of all RP cases are, in fact, Usher syndrome []. Deafness, generally congenital and stable, may be profound (type 1) or moderate/medium (type 2). In some cases deafness occurs during the first decade and worsens progressively (type 3). Mutations in at least 11 genes are responsible for Usher syndrome[].
  • Bardet Biedl syndrome (BBS) – is less frequent than Usher syndrome (prevalence 1/150,000 []). The phenotype is characteristic and associates RP (often of cone-rod dystrophy type) with obesity already present in childhood, mental retardation or mild psychomotor delay, post axial polydactyly, hypogenitalism and renal abnormalities that lead to renal failure. BBS is due to mutations in at least 11 genes [,], with cases of triallelic digenic inheritance []. The rare Alstrôm syndrome (due to ALMS1 gene mutation) resembles BBS and presents with deafness, diabetes mellitus and acanthosis nigricans.
  • Senior Loken syndrome (SLS) – associates an usually severe RP (sometimes diagnosed as LCA) with nephronophtisis (renal atrophy frequently evolving towards renal failure requiring transplantation), or sometimes a milder RP that is discovered later in life. At least four genes (NPHP1, NPHP3-5) encoding nephrocystins are involved in this disease [].
  • Alport syndrome – deafness and progressive nephritis are associated with yellow flecks around the macula, rather than with an authentic RP.
  • Cohen syndrome – associates RP to a particular facial dysmorphism (prominent upper incisors) with short stature, mental retardation, long and narrow hands, and neutropenia. One causative gene (COH1) that encodes a protein involved in vesicular trafficking, is related to this syndrome [].
  • Jeune syndrome – associates RP with a thoracic hypoplasia, brachydactyly and chronic nephritis. One locus has been identified (asphyxiating thoracic dystrophy, ATD).
  • Cockayne syndrome – is characterized by dwarfism, progeria, mental retardation, and retinopathy with fine granular spots.
  • Methylmalonic aciduria with homocystinuria – is caused by genetic defects in enzymes that metabolize vitamin B12. Rare cases present with macular atrophy, salt-and-pepper retinopathy, and vascular attenuation.
  • Abetalipoproteinemia (Bassen Korntzweig disease) – is characterized by progressive ataxia, steatorrhea, reduction of plasma lipids and pigmentary retinopathy that resembles retinitis punctata albescens in some cases.
  • Bietti’s disease – shows characteristic microcrystalline deposits in fundus and cornea. Patients undergo progressive RP evolving towards chorioretinal atrophy. The causative gene, encoding a form of cytochrome P450 (CYP4V2), has been recently discovered [].
  • Cystinosis – presents with typical crystal deposits in the cornea and pigmentary retinopathy in a highly photophobic patients with short stature. Accumulation of cystine in other body parts leads to hypothyroidism, diabetes mellitus, and renal failure. The causative gene (CTNS) encodes a protein (cystinosin) involved in the lysosomal transmembrane transport of cystein [].
  • Mucopolysaccharidoses – are characterized by facial and bony changes, mental retardation and corneal clouding. Only types I, II and III show pigmentary retinopathy.
  • Zellweger (cerebro-hepato-renal) syndrome.
  • Hyperoxaluria type I with retinal atrophy in spots.
  • Neonatal adrenoleukodystrophy with leopard spots in fundus.
  • Infantile Refsum disease – (caused by mutation in the PEX1PEX2 or PEX26 genes) presents with elevated phytanic acid and pigmentary retinopathy with characteristic prominent macular involvement.
  • Adult Refsum disease – caused by mutation in the gene encoding phytanoyl-CoA hydroxylase (PAHX or PHYH) or the gene encoding peroxin-7 (PEX7) presents with highly elevated phytanic acid, anosmia, deafness, and RP.
  • Peroxisomal disorders other than Refsum disease – except for the rhizomelic chondrodysplasia punctata, all children with disorders of peroxisomal assembly who survive long enough develop pigmentary retinopathy.
  • Neuronal ceroid lipofuscinosis – (also called Batten disease or amaurotic idiocies), associates mental retardation, seizures, ataxia and retinal degeneration. The retinal disease starts with macular involvement (red-cherry spot) and later spreads to peripheral retina. The protein, encoded by CLN3, is found in the lysosomes and in synapses [].
  • Joubert syndrome (JBTS) – is a phenotypically heterogenous syndrome that associates various central nervous system (CNS) developmental abnormalities including the so-called “molar tooth sign”, cerebellar vermis hypoplasia and cerebral cortex defects, with renal cysts, and pigmentary retinopathy. There are overlaps with Senior Loken syndrome, as NPHP1 is a causative factor in about 2% of JBTS4. Another causative gene, AHI1, has been recently discovered in the JBTS3 form [,]. There are two other loci (JBTS1-2).
  • Autosomal dominant cerebellar ataxia type II (SCA7) – shows a retinal disease, which often begins with a granular macula and then spreads out to the whole retina. It is due to trinucleotide expansions in the transcription factor ataxin-7 and anticipation effect is found [].
  • Myotonic dystrophy shows cataract and sometimes pigmentary retinopathy.
  • Hallervorden-Spatz syndrome – shows progressive dysarthria and dementia, iron deposition, and flecked type retinopathy with bull’s eye maculopathy.

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 bright lights)
  • 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

Diagnosis of Retinitis Pigmentosa

Functional signs

  • Night blindness (nyctalopia) is the earliest symptom
  • Photophobia appears later
  • The visual acuity is preserved in early and mid stages

Visual field

  • Patchy losses of peripheral vision evolving to
  • Ring shape scotoma, and eventually
  • Tunnel vision

Fundus

  • Pigmentary deposits resembling bone spicules, initially in peripheral retina
  • Attenuation of the retinal vessels
  • Waxy pallor of the optic disc
  • Various degrees of retinal atrophy

Electroretinogram

  • Dramatic diminution in a- and b-wave’s amplitudes
  • Scotopic system (rods) predominates over photopic (cones) system
  • Rod dysfunction as measured by one of the following:
    • Dark adaptation (elevated rod final threshold)
    • Electroretinogram (ERG) (nondetectable or severely reduced rod responses, with prolonged implicit time, often with lesser reduction and prolongation of cone-mediated responses)
  • Progressive loss in photoreceptor function
  • Loss of peripheral vision that often is greater superiorly but can involve other regions as well
  • Bilateral involvement that has a high degree of symmetry, with respect to both the severity and the pattern of visual field loss and retinal changes

The American Academy of Ophthalmology (AAO) Recommendations on Clinical Assessment of Patients with Inherited Retinal Degenerations include the following assessments

  • Ocular and medical history
  • Pedigree detailing the family history of eye disease
  • Clinical eye examination
    • Best corrected visual acuity (BCVA)
    • Slit lamp biomicroscopy
    • Intraocular pressure
    • Indirect ophthalmoscopy
  • Imaging
    • Color fundus photos
    • Fundus autofluorescence (reduced illumination when possible)
    • Spectral domain optical coherence tomography (sdOCT)
  • Visual fields
  • Full-field electroretinography (ffERG)
  • Molecular genetic testing (see Evaluation Strategy to Identify the Genetic Cause of Nonsyndromic Retinitis Pigmentosa)
  • Best corrected visual acuity (BCVA) – is measured in individuals age five years and older using the Snellen charts, for assessment of macular (central) vision both at distance (20′) and at near (14″).
  • Indirect ophthalmoscopy – of the retina in individuals with advanced RP is characterized by the presence of intraretinal clumps of black pigment, markedly attenuated retinal vessels, loss of retinal pigment epithelium (RPE), and pallor of the optic nerve. These changes reflect long-standing retinal degeneration and need not be present to make the diagnosis of RP. The fundus findings are, however, instrumental in distinguishing RP from other retinal dystrophies that have similar clinical findings but distinctive retinal changes.
  • Spectral domain optical coherence tomography (sdoCT) captures micron-resolution cross-sectional images of the retina, most typically of the macular region. It can be used to demonstrate which outer layers are involved in the retinal degeneration, measure retinal thickness, and help with the diagnosis and follow up of cystoid macular edema [].
  • Visual field testing – (also called perimetry) is the mapping of subjectively perceived test objects, which are ellipses of light varying in brightness and in size from 1/16 mm to 64 mm, projected on a uniformly illuminated background. Symptomatic defective dark adaptation in individuals with RP is usually accompanied by peripheral visual field defects or mid-peripheral scotomas (blind spots). In early RP, a ring scotoma often is present in the mid-periphery of the visual field approximately 20-25° from fixation.
  • Visual Acuity – Visually acuity is usually maintained until very late in the course of RP unless macular atrophy or cystoid macular edema is present. Visual acuity is variable, but in general vision loss is characterized as less severe in individuals with autosomal dominant RP than with autosomal recessive RP. Patients with X-linked RP typically have the worst visual prognosis [,].
  • Color Vision – Macular cone function can be assessed with color vision testing. Deficiency in blue cone function (acquired tritanopia) is characteristic of advanced RP. Individuals with vision worse than 20/30 and areas of macular atrophy correspond to poorer performance on color vision tests such as the Nagel anomaloscope and Farnsworth-Munsell 100-hue test. Those with autosomal dominant RP correlate to better color vision testing than those with other inheritance types [].
  • Electroretinography Conventional or full-field electroretinography (ERG) objectively demonstrates the overall functional status of the photoreceptors by measuring retinal electrical potential after light stimulation. A dim blue light (dark adapted) single flash induces a rod response and a flickering (30 Hz) white light elicits a cone response. Early and severe impairment of pure rod responses occurs in RP with a dramatic decrease in amplitude and implicit times of both a-waves (photoreceptor) and b-waves (signaling by second-order bipolar cells). Advanced RP patients have extinguished rod and cone responses [,].
  • Electro-Oculography – Electro-oculography (EOG) reflects a global outer retina and RPE function. When ERG findings are abnormal, EOG is also abnormal. In RP patients, its main utility may be in the evaluation of carriers with questionable funduscopic and ERG findings. In X-linked RP, EOG measurements are extinguished in RP patients and subnormal in RP carriers. EOG abnormalities have been found more often in RP patients over the age of 40 years [].
  • Optical Coherence Tomography Optical Coherence Tomography (OCT) is a non-invasive testing modality providing morphological information of the retina. It assesses the vitreoretinal interface, retinal contour and thickness, presence of intraretinal or subretinal fluid, and photoreceptor layer and RPE status. Compared to time-domain OCT, Fourier-domain OCT provides greater axial resolution and scanning speed allowing for more detail of the structural changes within the retinal layers, specifically the outer segment, inner segment, outer nuclear layer, as well as the RPE. The relationship between retinal structure and visual function has been studied in RP patients utilizing Fourier-domain OCT and automated perimetry as well as microperimetry [,].

Treatment of Retinitis Pigmentosa

  • Light protection – Clinical evidence and data from animal studies indicate that some genetic types of pigmentary retinopathies are partly light-dependent []. Thus, patients with pigmentary retinopathies are recommended to wear dark glasses outdoor. Wearing of yellow-orange spectacles minimizes photophobia. Eyeshade and lateral protection help to protect against dazzling side-coming light rays.
  • Vitaminotherapy – Vitamins A and E may protect the photoreceptors by trophic and anti-oxidant effects, respectively. Previous studies have demonstrated that long term (5–12 years) vitamin A supplementation at doses of 15,000 units per day slightly slowed down the loss in ERG amplitude, while vitamin E at 400 units per day had adverse effects []. However, the conclusions of this study were debated [], thus there is no consensus about the usefulness of vitamin A treatment. If vitamin A supplementation is proposed, levels of serum retinol (normal <3.49 μmol/l, i.e. <1 mg/l) and triglyceridemia (normal <2.13 mmol/l, i.e. <0.19 g/l) should regularly be checked, as well as liver enzymes (aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase) since vitamin A storage occurs mainly in this organ. Vitamin A should not be given to RP patients with mutations in ABCA4. In a recent study, patients were given docosahexaenoic acid (DHA) supplementation at 1200 mg/day, in addition to vitamin A. It was shown that the course of the disease was initially slowed down by the addition of DHA, but this beneficial effect did not last over 2 years [].
  • Gene therapy – This approach requires the implicated genes to be identified and therefore, the availability of efficient genotyping methods. The strategy is relatively simple for RP due to loss-of-function (usually recessively inherited). In this case, one expect that the expression of the wild-type cDNA in the appropriate cell (photoreceptor or RPE) will avoid cell death. However, it is more complicated for RP due to dominant negative pathogenic mechanisms in which the expression of the mutated gene should be inhibited, by use of ribozymes or siRNA for example. In the last 10 years, studies have been carried out in several animal models. Although all showed a significant rescue of photoreceptors, there was still progressing photoreceptor cell death, which could be due to an inappropriate expression level of the therapeutic gene and to an insufficient percentage of transduced photoreceptors. The most advanced studies have been performed for LCA in a large animal model (the Briard dog) in which the surgical administration in the subretinal space of AAV vectors carrying the RPE65 cDNA allowed to restore vision in four month-old dogs in USA [,] and in France []. Five years later, the dog vision seems stable, although the very long-term efficiency still remained to be ascertained. Promising results have been obtained in a mouse model of X-linked retinoschisis []. It is expected human trials in RPE65 patients to be carried out soon in the USA, UK, France, and other countries.
  • Pharmacological treatment Pharmacological agents can compensate for a biochemical defect, and enhance or inhibit the activity of various effectors. Calcium-channel blockers have been tried in several animal models of RP [], yet with limited success []. Another example is Stargardt disease in which the use of visual cycle inhibitors has been shown to slow down the toxic accumulation of lipofuscin in the RPE in a mouse model [,]. Supply of 9-cis retinal has been shown to restore the rod activity in a Rpe65-/- mouse model of LCA []. NAD analogues supply in RP due to IMPDH1 defects may also be efficient []. It might be speculated that the alternative of pharmacological treatments would be explored in more details in the future, as the mechanisms of the various forms of RP will be progressively unraveled.
  • Acetazolamide – In the later stages, the tiny area at the center of your retina can swell. This is called macular edema, and it, too, can reduce your vision. This medication can ease swelling and improve your vision.
  • Coping with photoreceptor cell death – A general problem with the treatment of the primary cause of the disease is that beyond certain stage in the evolution, non-cell autonomous mechanisms leading to cell death may overwhelm the potential benefits of gene- or pharmacological therapies. Cell death may be due to the release of proapoptotic signals in the photoreceptor environment, or to the lack of survival factors normally produced by the living cells. The latter has been confirmed by the discovery that rods produce factors that are necessary for cone survival []. Thus, in typical RP, rods die because they express a mutated gene, and cones, which do not express the mutated gene, are secondarily degenerating because of the lack of rod factors. Therefore, the supply of rod factors in the retina would protect cones against secondary degeneration.
  • Neuroprotection using growth factors – Several growth factors, including ciliary neurotrophic factor (CNTF), glial-derived neurotrophic factor (GDNF), cardiotrophin-1, brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF) have some efficacy in animal models, that varies from one model to another. Their short half-life requires their delivery in situ. Since iterative intravitreal injections are not recommended, several strategies like use of encapsulated cells producing bFGF placed in the vitreous cavity [] and gene transfer of GDNF in resident cells [] have been tried. These factors, however, have side effects including retinal neovascularization and cataract. For example, CNTF allows an excellent preservation of retinal integrity in several animal models, but it causes a decrease in the ERG response of the retina by yet unknown toxic mechanism []. Nevertheless, encapsulated cells releasing CNTF of vitreous of patients with RP is currently under Phase I clinical investigation [].
  • Neuroprotection using antiapoptotic factors – In animal models, gene transfer of anti-apoptotic bcl-2 slows down the photoreceptor cell death [] as well as the use of an inhibiting peptide of caspase-3 [].
  • Rod-derived cone viability factor –  Identified a rod-derived cone viability factor (RdCVF) that appears to be a truncated thioredoxin-like protein which significantly delays cone death in the rd1 mouse model of RP. Studies are ongoing to test whether this factor will be efficient in other forms of RP.
  • Restoration of visual function – Beside therapies aimed at preserving visual function and preventing cell death, one would like to find out ways of restoring the visual function. This is a tremendous challenge since (as a general rule for neurons in the CNS) human photoreceptors are not produced and do not divide after birth, therefore, their loss is irreversible. In addition, the loss of photoreceptors leads to a dramatic remodeling of the retinal circuits which would probably modify the visual information process if correct implantation of new photoreceptors was possible. Nevertheless, numerous teams are now working to achieve visual restoration either by photoreceptor replacement or by means of artificial devices.
  • Cell or tissue transplantation – Experiments have been tried to transplant retinal cells from fetuses or adult retina in humans, and layers of photoreceptors or even entire retina in animals models (rats and rabbits). Generally, the survival of transplanted photoreceptors is readily observed, but they do not properly organize in the retina (forming rosettes) and lack, with rare exceptions, functional synapses. Researchers are also becoming interested by using stem cells, embryonic or adult, from retina or from other tissues. Although very interesting to study, these therapeutic approaches are still far from realistic use in a near future.
  • Retinal prosthesis – Microphotodiodes arrays that replace degenerated photoreceptors or more sophisticated devices that capture light and stimulate the retina, optic nerve or visual cortex have been developed. Several clinical trials have essentially demonstrated the tolerance of the implanted devices. Today, they represent the basis for further studies towards improvement of the future devices resolution.
  • Vitamin Therapy – Vitamin A may protect the photoreceptors by trophic and antioxidant effects. Long-term (5 to 15 year) vitamin A supplementation in doses of 15,000 IU per day slowed down the loss of ERG amplitudes []. Vitamin E at 4,000 IU had an adverse effect []. Clinicians continue to debate the conclusions of these studies []. There is no consensus about the utility of vitamin A treatment. Vitamin A should not be given to patients with RP caused by mutations in the ABCA4 gene. In another study, RP patients were given docosahexaenoic acid (DHA) supplementation at 1200 mg/day in addition to vitamin A []. This study showed that the disease course was initially slowed by the addition of DHA; however, the beneficial effect did not last beyond two years. Berson and colleagues have reported on the benefits to RP patients of a diet rich in omega-3 fatty acids []. RP patients taking vitamin A palmitate, but not DHA capsules, benefited from an omega-3 rich diet (equivalent to eating salmon, tuna, mackerel, herring, or sardines, once to two times a week). Recently, Berson and colleagues reported on patients taking Vitamin A randomly assigned to either lutein supplementation (12 mg/da) or placebo over a four year period [].
  • Sunglasses – These make your eyes less sensitive to light and protect your eyes from harmful ultraviolet rays that may speed vision loss.
  • Retinal implant – If you have late-stage RP, you may be a candidate a retinal implant that could provide partial sight. Argus II is the implant available in the US. It’s implanted into a single eye and paired with glasses equipped with a camera. Images are converted to electrical pulses that are sent to the retina. Many were able to locate lights and windows. Some were able to determine where other people were located in a room and about half of the subjects were able to read letter that were about 9 inches high.
  • Electrical Stimulation Therapy – For patients with early and intermediate-stage RP, electrical stimulation therapy (EST) of the eye may help preserve vision that otherwise would be lost to the disease, according to representatives of Okuvision, a German medical device company founded by Retina Implant AG, at the 2011 ARVO meeting.

Other treatments under review include

  • Replacement of damaged cells or tissues with healthy ones
  • Gene therapy to put healthy genes into the retina
  • Devices and tools can help you make the most of your vision, and rehab services can help you stay independent.

References

Does Everyone With Retinitis Pigmentosa Go Blind

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  2. Scanditrade Baltic OU is one of the leading companies market of deep wood processing, offering multiple solutions for industrial construction, house building, machinery construction, furniture manufacturing and other areas related with the birch plywood application.
    Birch plywood (exterior interior)
    Standard sizes, mm 1525×1525, 1220x2440x1220, 1250x2500x1250, 1500/1525×2440/2500, 2440/2500×1500/1525, 1500/1525×3000/3050
    Grading – I (B,S) II (BB) III (CP) IV (C)
    Surface quality – One side sanded (S1S), outer layers sanded (S2S), unsanded (NS)
    Formaldehyde emission class – E0, E1
    Film faced plywood(F/F)(F/W)
    Standard sizes,mm 1220x2440x1220,1250x2500x1250
    Grading-I,II
    Film density,g/m-120-400
    Birch, Beech, Oak bed slats:
    Length, mm: 200-2500
    Width, mm: 25-230
    Thickness, mm: 8-40
    Radius: Flat, mm: 2.7–8
    We are able to deliver according to DAP DDP CIF CFR
    Yana Ch
    http://www.baltic-wood.com
    info@baltic-wood.com

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