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

Intracellular disk

Disk membrane

Connectingcilium

outer segmentouter segment

Disk membrane

Intracellularspace

Extracellularspace

Visualpigment

Visualpigment

Extracellularspace

Plasmamembrane

Intracellularspace

Connectingcilium

Rods and Cones

ROD CELL CONE CELLPHOTORECEPTORS IN THE EYE

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 Rhodopsin

Through a complex chain of chemical changes activated by light ,Rhodopsin begins the events that activates the phototransduction cascade

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.

Nyctalopia : In greek : Nykt – night , alaos – blindness Condition in which inability to see in relative dim light.

Causes :1. Vitamin A deficiency2. Retinitis pigmentosa3. Uncorrected refractive error - Myopia4. Media opacification - cataract5. Following pan retinal photocoagulation6. Congenital stationary night blindness7. Hydroxychloroquine & Phenothiazine8. Advanced glaucoma

Medical history to be sought Operations [intestinal surgeries] Liver diseases Use of medicine :Hydroxychloroquine

Phenothiazine Hearing status( RP, Usher’s Syndrome, Refsum’s)

Mental retardation( BBS,LMS) Renal disease (BBS) Heart disease (KSS, Refsum’s)

Introduction: 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 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.

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 Scotoma

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]

Signs : 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

Associated ocular problems

Myopia Subcapsular cataract Open angle glaucoma Keratoconus Posterior vitreous detachment

Atypical RP

Retinitis pigmentosa albescens Sector RP Unilteral RP Pericentric RP

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

Systemic findings

Bassen Kornzweig syndrome Refsum’s syndrome Kearns Sayre syndrome Bardet – Biedl syndrome Usher’s syndrome

Diagnosis

Refraction Direct ophthalmoscopy Indirect slit lamp biomicroscopy Visual field evaluation Dark adaptametry Electroretinography

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 diet

Systemic carbonic anhydrase inhibitors like

acetazolamide & Intravitreal triamcinolone

Neurotrophic factors

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 Genetic counselling

ARMD

Degenerative anomaly of macula –exaggeration of normal ageing –Visual threatening disability

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:

PATHOGENESIS Impaired metabolism of RPE

Accumulation of metabolic debris in bruch membrane

Thickening and fragmentation of bruch membrane with damage

Choroidal neovascularization

Hereditary factors, age, nutrition, smoking, hypertension ,high cholestrol and exposure to sunlight are risk factors.

CLINICAL FEATURES

Gradual painless diminution of vision Metamorphopsia - distorted vision. Central scotoma & Paracentral scotoma

OPHTHALMOSCOPY

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 present.

DRY ARMD

WET ARMD with haemorage

MANAGEMENT

Amsler grid ,preferential hyperacuity tests Provide micronutrients [zinc & Antioxidants] Avoid UV light Life style changes Laser photocoagulation Photodynamic therapy Anti –VEGF Transpupillary thermotherapy

MANAGEMENT

Surgical treatment :

Sub macular surgery

Macular translocation

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