“A ray of hope is sometimes all the sunshine we need!”
Someone very wise
The retina is a thin piece of light sensitive tissue lining the back of the eye. Photoreceptors are specialized cells in the retina that convert light into electrical signals that the brain interprets as vision. There are two general types of photoreceptors, called rods and cones. Rods are in the periphery of the retina and allow us to see in dim and dark light. Cones reside mostly in the central portion of the retina and allow us to perceive fine visual detail and colour. Degeneration of these photoreceptors causes/results in what is known as Retinitis pigmentosa.
Retinitis pigmentosa (RP), or pigmentary retinal dystrophy denotes a clinically and genetically diverse group of inherited diffuse retinal degenerative diseases that involve a breakdown and loss of retinal photoreceptors. Initially and predominantly affects the rod photoreceptors, with later degeneration of cones (rod cone dystrophy),often leading to legal and sometimes complete blindness. The term retinitis pigmentosa (RP) is a misnomer since there is neither inflammation, nor pigmentation sine qua non. Its prevalence is approximately 1:5000.
RP is an inherited disorder that results from harmful changes in any one of more than 50 genes that carry the instructions for making proteins needed in the photoreceptors or producing a protein that is toxic to the cell. RP may occur as a sporadic (simplex) disorder or genetic mutations can be passed from parent to offspring in three different ways— autosomal recessive, autosomal dominant, or X-linked.
Autosomal recessive RP – Most common. Both parents carry one copy of the mutated gene and are referred to as unaffected carriers. Each of their children has a 25 percent chance of being affected.
Autosomal dominant RP – Usually one parent is affected and has a 50% chance of passing it to each child.
X-linked RP– Least common but most severe form. The mutated gene for the disease is located on the X chromosome. Female carriers have a 50 percent chance of passing the gene to their daughters, who become carriers and a 50 percent chance of passing the gene to their sons, who are then more severely affected by the disease.
In 20–30% of cases, RP, often atypical is associated with a systemic disorder (syndromic RP); these conditions are usually of AR or mitochondrial inheritance.
- Loss of night vision -Vision may be normal during the day but as the disease progresses, it takes longer to adjust to the darkness. One may stumble over objects or have trouble driving at dusk and at night, find it hard to see in movie theatres or other dim rooms.
- Gradual loss of peripheral (side) vision – This is known as “tunnel vision.” One may find bumping into things as you move around because he/she may not able to see objects below and around without turning the head.
- Loss of central vision- Generally occurs in the advanced stage. Makes it hard to do detailed tasks such as reading or threading a needle.
- Photophobia – One might find bright lights uncomfortable.
- Photopsia- One may start to see flashes of light that shimmer or blink.
- Visual acuity (VA) may be normal; contrast sensitivity is affected at an earlier stage than VA.
The classic triad of findings of typical RP comprises
- “Bone-spicule” brownish intraneural retinal pigment.
- Attenuation of retinal arterioles.
- Gliotic “waxy pallor” of the optic nerve head.
- Thinning and atrophy of the RPE in the mid- and far-peripheral retina.
- Relative preservation of the RPE in the macula but may show atrophy, epiretinal membrane (ERM) formation and cystoid macular oedema (CMO).
- Female carriers of the XLR form may have normal fundi or show a golden-metallic reflex at the and/or small peripheral patches of bone spicule pigmentation.
OTHER OCULAR ASSOCIATIONS
- Posterior subcapsular cataract (common in all forms of RP).
- Optic disc drusen
- Posterior vitreous detachment
- Open-angle glaucoma (3%)
- Keratoconus (uncommon)
- Electroretinogram (ERG) measures the electrical activity of photoreceptor cells. In early disease it shows reduced scotopic rod and combined responses; photopic responses reduce with progression, and eventually, the ERG becomes extinguished. Multifocal ERG may provide more specific information.
- Electrooculogram (EOG) may be subnormal, with the absence of the light rise.
- Dark adaptation measures visual sensitivity and is prolonged in RP.
- Contrast sensitivity is a more sensitive test of macular function and is reduced in RP.
- Optical coherence tomography (OCT) will identify macular edema if any.
- Visual field testing (Perimetry) determines the extent of vision loss. Initially demonstrates small mid-peripheral scotomata that gradually coalesce and may deteriorate to leave a tiny island of residual central vision that may subsequently be extinguished.
- Microperimetry is useful for central visual assessment.
- Genetic testing is diagnostic. It may identify the particular mutation responsible in an individual patient and facilitate genetic counseling, including the risk of transmission to offspring.
Treatment of allied ocular conditions
- Refractive error –Accurate correction of ametropia should be provided to all patients.
- Cataracts – Its removal may lessen glare and improve visual acuity.
- Glaucoma – The prevalence of primary open angle glaucoma and angle closure glaucoma in patients with RP ranges from 2-12% and 1.03% respectively. Its timely treatment prevents the additional vision loss.
- Macular edema and epiretinal membranes – Oral and/or topical carbonic anhydrase inhibitors and vitreous surgery to peel this membrane with removal of annoying vitreous opacities respectively, may benefit few patients.
Currently there are a lot of ongoing research aimed at reducing progression and improving functional vision. Some of the frontiers in area of research for cure are:
- Retinal chip research (one such device is Argus II Retinal Prosthesis System)
- Gene therapy (RPE 65 gene)
- Stem cell therapy
- Analysis of leukocyte DNA
- Hormone oestrogen injection
Visual rehabilitation and lifestyle modifications
- Nutritional supplements– high daily doses of vitamin A palmitate (15000 IU/day) andomega-3 and omega-6 fatty acid supplementation have been tried but its hypertoxicity related harmful effects discourage its use. Hence, it is not recommended any more.
- Optical aids
For Distance and Intermediate Distance
Telescopes Types of telescopes
- Galilean or Keplerian
- Hand-held, spectacle-mounted, or clip-on
- Monocular or binocular
- Fixed focus, focusable telescope, or autofocus
For near tasks
- High-plus spectacles (microscopes)
- Hand-held magnifier
- Stand magnifier
- Telescope system for near (tele microscope)
- When you watch TV, read books or see mobile phone. For every 30min you need to take 5min rest, close your eyes for 5min or go outside and look at a distance.
- Eat healthy food with lutein, like corn, carrots, and blueberries and eat fresh vegetables and fruits, fresh sea food also benefits the retina.
- In this era, technology is a boon for RP patients. Electronic devices include video magnifier systems, closed-circuit televisions, Bluetooth connections to smart projectors, large-print computer programs such as Zoom Text, screen readers such as Virtual Vision and Jaws, and computer tabletsenhances your reading and learning ability.
- Many patients with severe vision loss also have significant reduction of contrast sensitivity. Daily activities can be supported with aids such as black felt-tipped pen, bold lines, and contrasting colours. For example, simple lifestyle modifications like dark colour doors with light coloured handles or making a dark coloured line on lighter coloured flooring may help them walk through their house confidently.
- Use UV-absorbing sunglasses and brimmed hats during outdoor activities. To be specific absorptive lenses in yellow for low-light environments and amber for more intense lighting are good prescription options.
- A type of scope, caps or visors, side shields, and/or polarizing lenses are prescribed to control the reflection of light. A typoscope can also be used as a guide to reading, writing, and signature in cases of large defects of the visual field.
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