Discuss Night Blindness!


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Discuss Night Blindness! - Dr James Beatty

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Discuss Night Blindness!

  1. 1. Discuss Night Blindness!Discuss Night Blindness! J.Beatty
  2. 2. OverviewOverview Physiology Tests Classification: – Normal physiological response – Acquired – Congenital Focus on vitamin A and R.P.
  3. 3. PhysiologyPhysiology -Exposure to strong light decreases visual sensitivity, but increases visual acuity/discrimination and temporal acuity/discrimination. -Exposure to dark increases light sensitivity, but decreases visual acuity and temporal acuity.
  4. 4. -Mechanisms of adaptation are: Pupil: change in size, very rapid response. Rods and cones: duplex theory of vision (with increased retinal illumination , vision changes from a rod to cone dominated system), slow response. Photopigment: rhodopsin regeneration in the dark, slow response. Automated gain control: very rapid response Cellular mechanisms: photoreceptors, bipolar cells, ganglion cells. Very rapid response.
  5. 5. TestsTests Goldman-weekes adaptometry: The patient is adapted to a standard light, which is than turned off and the patient is then presented with test stimuli. The lowest perceivable intensity is then recorded against time.
  6. 6. ClassificationClassification Normal physiological response: When moving from a bright to a dark room. Initial blindness followed by good discrimination by 10 mins (cones), and max adaptation by 10 to 20 min (rods).
  7. 7. Acquired causes: -Pathological myopia: ? chorioretinal atrophy -Undercorrected myopia: ? abberations -Early prebyopia: ? decreased accommodation in the dark -Vitamin A deficiency: necessary for making photopigments/rhodopsin. Causes = inadequate diet, malabsorption, alchoholism, cirrhosis, ? measels and pregnancy. Marked night blindness, numerous small yellow- white, well demarcated spots deep in the retina seen peripherally. Also dry eye, Bitot spots and Xerophthalmia.
  8. 8. -Zinc deficiency (needed for vit A metabolism) -Advanced glaucoma and other causes of severe optic atrophy. -Diffuse opacification of the media: cataract, vitreous opacities, ect. -Hysteria or malingering. -End stage syphalitic neuroretinitis. -Cancer-related retinopathy. -Drugs. Isotretinoin (used in acne), ?others.
  9. 9. Congenital causes: Congenital stationary night blindness: normal fundus: -AD types: Nougart type, decreased rod and cone ERG. Riggs type, normal cone ERG. -AR or XL congenital nyctalopia with myopia. abnormal fundus -Oguchi disease: 2-12 hrs to attain normal dark- adapted rod thresholds. - Fundus albipunctatus: multipal yellow-white spots, sparing the fovea, erg and eog abn, but revert to normal on prolonged dark adapration.
  10. 10. -Gyrate atrophy: AR, high levels of ornithine, multipal sharply defined areas of chorioretinal atrophy separated by pigment margins. -Choroideremia: XL recessive, diffuse RPE and choroidal atrophy throughout the fundus. -Vitreoretinal dystrophies: esp Goldmann- Favre disease
  11. 11. Retinitis Pigmentosa Prevalence: 1:5000 Inheritence: Isolated, Autosomal dominant (mild), Autosomal recessive (severe), X-linked (most severe). Clinical: Nyctalopia, arteriolar attenuation, RP sine pigmentosa, Retinitis puncta albescens, Bone spicules, unmasking of choroidal vessels, maculopathy, vitreous changes, waxy disc.
  12. 12. Erg: first reduced scotopic and combined, later photopic. Eog: subnormal. Dark adaptometry: prolonged. Colour vision: normal. Perimetry: annular mid peripheral scotoma, progress to small central field. FA: diffuse hyper (unmasking) and areas of hypo (masking by bone spicules).
  13. 13. Prognosis: poor , 25% maintain good reading VA, most pts less than 20yrs have VA > 6/60, by 50 yrs most have VA < 6/60. Ocular associations: post. sub cap. Cataract, open angle glaucoma, myopia, keratokonus, vitreous changes, optic disc drusen. Atypical RP: Sector RP, pericentral RP (along the arcades), RP with exudative vasculopathy (coats like appearance in periphery)
  14. 14.  Systemic associations:  -Bassen-kornzweig syndrome: due to B- lipoproteinaemia deficiency. Ataxia, acanthocytosis in blood, ophthalmoplegia, ptosis. Treat with Vit E)  -Refsum disease: AR inborn error of metabolism with increased phytanic acid in serum, multiple CNS abn, retina more salt and pepper like)  -Usher syndrome: AR, 5% of all profound deafness in children and half of all blind and deaf.  -Kearns-Sayer syndrome: mitochondrial DNA deletions. Atypical RP with central clumping.  -Bardet-Biedel syndrome: mental handicap, polydactyly, obesity and hypogenitalism.