Neurophysiology of Eye

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NEUROPHYSIOLOGY OF EYEVISUAL ACUITY, ACCOMMODATION, PUPILLARY REFLEXES, VISUAL PATHWAYS, INTRAOCULAR PRESSURE.

VISUAL ACUITY, It is the most important criterion of testing the functional integrity of the eye Distance vision is assessed from 6 meters.

Near vision- 14 inches from the eye.

VISUAL ACUITY,V A of infants and children

Age 6-8weeks 5 months 18-24 months 2-3 years >3 years

Snellens acuity (20/600) 6/1800 (20/60) (20/40) (20/30) (20/20) 6/18 6/12 6/9 6/6

VISUAL ACUITY, V A of infants and children -Occlude one eye and observe the behaviour -Cover test for fixation -Electroretinogram (ERG) -Visual evoked response (VER) -Opticokinetic nystagmus (OKN)

VISUAL ACUITY,V A of infants and children Very young and infants

VISUAL ACUITYV A of infants and children Very young and infants

VISUAL ACUITY,

VISUAL ACUITY,V A of infants and children (6 months old and above)

VISUAL ACUITY,

V A of infants and children

VISUAL ACUITY,(2-3 years)

VISUAL ACUITY,

V A of infants and children (Preschool children)

VISUAL ACUITY,

VISUAL ACUITY,

Adult with snellens visual acuity chart

VISUAL ACUITY,

VISUAL ACUITY,

VISUAL ACUITY,

Near visual acuity

The pupil NEAR REACTION HAS A TRIAD OF ACTIONS. -Convergence of eyes-Accommodation of the lenses -Miosis of the pupil

The pupil AccommodationFunction of:-inner radial muscle -outer longitudinal muscle of cillary body *contraction of the round muscle shortens the diameter of circle *Lens by virtue of its own elasticity tends to assume a more spherical shape for near objects

Accommodation The refractive power of the lens 20 diopters can be increased up to 54 diopters in young Stress on the suspensory ligaments change the shape of the lens contraction of circular muscle- spherical lens relaxation of circular muscle -flat lens for distance vision Controlled by parasympathetic supplyit increases its refractive power capable of focusing on near objects.

Pupillary reflexes Iris increase the amount of light that enters the eye during dull illumination decrease the amount of light that enters the eye in bright illumination By changing the size of the pupil

Pupillary reflexes

Pathway of the pupillary light reflex

Light & near input to EW nucleus

Presbyopia When a person is old lens grows larger and thicker loosing its elasticity lens remains totally non-accommodating to see near use hypermetropic correction (+ diopteric lens)

Oculo sympathetic pathway

7th nerve& lacrimal gland innervations

NEUROPHYSIOLOGY

NEUROPHYSIOLOGY

Intraocular pressure Aqueous secretion * Active secretion 80% of aqueous production by nonpigmented ciliary epithelium via active metabolic process *Passive secretion 20% of production ultrafiltration,diffusion depend on BP,plasma oncotic pressure& IOP

Intraocular pressure Factors determine the level of IOP Rate of aqueous secretion Resistance encountered in the outflow channels Level of episcleral venous pressure Normal IOP 10mmHg to 21mmHg Diurnal variation high IOP in the morning lower in the afternoon

Intraocular pressure Methods of examination tonometry *indentation- Schiotz tonometer *applanation-Goldman -The Perkins -The air puff -The Pulsair -The Tono pen

Noncontact pulsair Schiotz tonometer

perkins

tonopen