Discuss Night Blindness!Discuss Night Blindness!
– Normal physiological response
Focus on vitamin A and R.P.
-Exposure to strong light decreases visual
sensitivity, but increases visual
acuity/discrimination and temporal
-Exposure to dark increases light sensitivity,
but decreases visual acuity and temporal
-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.
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
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).
-Pathological myopia: ? chorioretinal atrophy
-Undercorrected myopia: ? abberations
-Early prebyopia: ? decreased accommodation in the
-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
-Zinc deficiency (needed for vit A metabolism)
-Advanced glaucoma and other causes of severe
-Diffuse opacification of the media: cataract,
vitreous opacities, ect.
-Hysteria or malingering.
-End stage syphalitic neuroretinitis.
-Drugs. Isotretinoin (used in acne), ?others.
Congenital stationary night blindness:
Nougart type, decreased rod and cone ERG.
Riggs type, normal cone ERG.
-AR or XL congenital nyctalopia with myopia.
-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.
-Gyrate atrophy: AR, high levels of ornithine,
multipal sharply defined areas of
chorioretinal atrophy separated by pigment
-Choroideremia: XL recessive, diffuse RPE
and choroidal atrophy throughout the
-Vitreoretinal dystrophies: esp Goldmann-
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.
Erg: first reduced scotopic and combined,
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).
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
-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.