Visual pigment in Rods : Rhodopsin
- glycoprotein and chromophore
- Peak absorption at 500 nm wavelength [blue]
- Most sensitive in dark adapted eye .
- Hence blues and greens will appear
brighter at nightfall - Purkinje effect
PHOTORECEPTORS IN THE EYE
Rods and Cones
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 .
The key to the rod’s ability to convert light
to electric impulses is the Visual pigment
Through a complex chain of chemical
changes activated by light ,Rhodopsin
begins the events that activates the
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.
In greek : Nykt – night , alaos – blindness
Condition in which inability to see in relative dim light.
Vitamin A deficiency
Uncorrected refractive error - Myopia
Media opacification - cataract
Following pan retinal photocoagulation
Congenital stationary night blindness
Hydroxychloroquine & Phenothiazine
Medical history to be sought
Operations [intestinal surgeries]
Use of medicine :Hydroxychloroquine
Hearing status( RP, Usher’s Syndrome, Refsum’s)
Mental retardation( BBS,LMS)
Renal disease (BBS)
Heart disease (KSS, Refsum’s)
Progressive Rod/cone dystrophy
Hereditary, progressive dystrophies of the
photoreceptors and RPE of Retina
Otherwise known as pigmental retinal dystrophy.
The condition is abiotrophic in nature and is
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.
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
As 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]
Characteristic fundus changes :
Black bone spicule /Corpuscular retinal pigments
[denser in mid periphery retina ]
Attenuated retinal blood vessels
Waxy type of optic disc atrophy
Cystoid macular edema
Retinitis pigmentosa albescens
Retinitis pigmentosa sine pigmento: with
same symptoms but without visible retinal
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
Indirect slit lamp biomicroscopy
Visual field evaluation
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 diet
Systemic carbonic anhydrase inhibitors like
acetazolamide & Intravitreal triamcinolone
Low vision aids, including telescopic and
magnifying lenses, night vision scopes help people
maximize the vision that they have remaining.
Ultraviolet protective sunglasses
Parental and supportive care
Degenerative anomaly of macula –
exaggeration of normal ageing –Visual
This 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:
Impaired metabolism of RPE
Accumulation of metabolic debris in bruch membrane
Thickening and fragmentation of bruch membrane
Hereditary factors, age, nutrition, smoking,
hypertension ,high cholestrol and exposure
to sunlight are risk factors.
Gradual painless diminution of vision
Metamorphopsia - distorted vision.
Central scotoma & Paracentral scotoma
Dry type - Hallmark is drusen and loss of
RPE. Drusen are small yellowish deposits
on bruch’s 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