Night blindness, or nyctalopia, can be caused by normal physiological responses to changes in light levels, acquired conditions like vitamin A deficiency, or congenital disorders. Tests like adaptometry measure a patient's ability to see in low light levels over time as their eyes adapt from light to dark. Congenital causes of night blindness include various forms of retinitis pigmentosa, an inherited retinal degeneration characterized by night vision loss and peripheral vision loss over time. Retinitis pigmentosa has many subtypes depending on inheritance and can be associated with other ocular and systemic findings.

1. Discuss Night Blindness!Discuss Night Blindness!
J.Beatty

2. OverviewOverview
Physiology
Tests
Classification:
– Normal physiological response
– Acquired
– Congenital
Focus on vitamin A and R.P.

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. -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. 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. 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. 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. -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. 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. -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. 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. 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. 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.  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.