nyctalopia & retinitis pigmentosa

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  • 1. Visual pigment in Rods : Rhodopsin - glycoprotein and chromophore [Opsin] [retinal] - Peak absorption at 500 nm wavelength [blue] - Most sensitive in dark adapted eye . - Hence blues and greens will appear brighter at nightfall - Purkinje effect

2. outer segmentouter segmentIntracellular disk Disk membrane Intracellular spaceDisk membraneVisual pigmentExtracellular spaceExtracellular spaceVisual pigmentIntracellular spaceConnecting ciliumConnecting ciliumROD CELLPlasma membraneCONE CELLPHOTORECEPTORS IN THE EYERods and Cones 3. Physiology of night vision :Rods are elongated cells [120 million in number ] mainly confined in the periphery of the retina. These are meant for Dim vision in low light .Rods, are extremely light sensitive and their sensitivity is about 500 times greater than the sensitivity of cones.Only a small number of photons is required to stimulate a rod to send a signal to the brain. Also more number of pigments than cones . 4. The key to the rods ability to convert light to electric impulses is the Visual pigment Rhodopsin Through a complex chain of chemical changes activated by light ,Rhodopsin begins the events that activates the phototransduction cascade 5. Dark adaptation : When a person shifts from bright to dim environment 2 processes occur - Pigment regeneration - Photochemical changes [Phototransduction] All this happens in a period of 30 minutes. 6. Nyctalopia : In greek : Nykt night , alaos blindness Condition in which inability to see in relative dim light.Causes : 1. 2. 3. 4. 5. 6. 7. 8.Vitamin A deficiency Retinitis pigmentosa Uncorrected refractive error - Myopia Media opacification - cataract Following pan retinal photocoagulation Congenital stationary night blindness Hydroxychloroquine & Phenothiazine Advanced glaucoma 7. Medical history to be sought Operations [intestinal surgeries] Liver diseases Use of medicine :Hydroxychloroquine Phenothiazine Hearing status( RP, Ushers Syndrome, Refsums) Mental retardation( BBS,LMS) Renal disease (BBS) Heart disease (KSS, Refsums) 8. Introduction: Progressive Rod/cone dystrophy Hereditary, progressive dystrophies of the photoreceptors and RPE of Retina Otherwise known as pigmental retinal dystrophy. 9. The condition is abiotrophic in nature and is genetically determined.Various inheritance patterns [AD,AR, X linked]In majority of families it occur as recessive trait., occasionally it shows dominant hereditary and even sex linked inheritance. 10. Symptoms : Patient presents with symptoms which become apparent between ages of 10 and 30 yrs. Night vision problems / prolonged dark adaptation Slow progressive loss of vision [peripheral] Sparing of central vision Ring ScotomaAs the disease develops, people with RP may often bump into chairs and other objects as side vision worsens and they only see in one direction - straight ahead.[Tunnel vision] 11. Signs : Characteristic fundus changes :Black bone spicule /Corpuscular retinal pigments [denser in mid periphery retina ]Attenuated retinal blood vesselsWaxy type of optic disc atrophyCystoid macular edema 12. Associated ocular problems Myopia Subcapsular cataract Open angle glaucoma Keratoconus Posterior vitreous detachment 13. Atypical RP Retinitis pigmentosa albescens Sector RP Unilteral RP Pericentric RP 14. VARIANTS Retinitis pigmentosa sine pigmento: with same symptoms but without visible retinal pigmentation. Retinitis puncta albescens: is an allied condition with same history and symptoms but here the retina shows hundreds of small white dots distributed uniformly over the whole fundus 15. Systemic findings Bassen Kornzweig syndrome Refsums syndrome Kearns Sayre syndrome Bardet Biedl syndrome Ushers syndrome 16. Diagnosis Refraction Direct ophthalmoscopy Indirect slit lamp biomicroscopy Visual field evaluation Dark adaptametry Electroretinography 17. Treatment Eminently unsatisfactory since, despite many claims, nothing appears to have a desired influence upon the course of the disease.but there is research that indicates that vitamin A supplementation and lutein may slow the rate at which the disease progresses.Antioxidants , omega-3 fatty acid, DHA.Low phytol and low phytanic acid dietSystemic carbonic anhydrase inhibitors like acetazolamide & Intravitreal triamcinolone 18. Neurotrophic factorsLow vision aids, including telescopic and magnifying lenses, night vision scopes help people maximize the vision that they have remaining.Ultraviolet protective sunglassesParental and supportive care Genetic counselling 19. ARMD Degenerative anomaly of macula exaggeration of normal ageing Visual threatening disabilityThis is one of the leading cause of blindness in the world. More common >65 years and in whites and females. TYPES: 1. Dry or atrophic type: 2.Wet or exudative type: 20. PATHOGENESIS Impaired metabolism of RPEAccumulation of metabolic debris in bruch membraneThickening and fragmentation of bruch membrane with damageChoroidal neovascularization 21. Hereditary factors, age, nutrition, smoking, hypertension ,high cholestrol and exposure to sunlight are risk factors. 22. CLINICAL FEATURES Gradual painless diminution of vision Metamorphopsia - distorted vision. Central scotoma & Paracentral scotoma 23. OPHTHALMOSCOPY Dry type - Hallmark is drusen and loss of RPE. Drusen are small yellowish deposits on bruchs membrane derived from metabolic products of visual receptors and RPE deposited as lipid Exudative type Hallmark is CNV elevated area in neuro sensory retina or pigment epithelium beneath which abnormal blood vessels, fluids or haemorrhage are present. 24. DRY ARMD 25. WET ARMD with haemorage 26. MANAGEMENT Amsler grid ,preferential hyperacuity tests Provide micronutrients [zinc & Antioxidants] Avoid UV light Life style changes Laser photocoagulation Photodynamic therapy Anti VEGF Transpupillary thermotherapy 27. MANAGEMENT Surgical treatment : Sub macular surgery Macular translocation 28. THANK YOU