OCULOMOTOR SYSTEM RETINA THE INNERMOST TUNIC OF THE

OCULOMOTOR SYSTEM

RETINA THE INNERMOST TUNIC OF THE EYE IS RETINA.

THE STRUCTURE OF THE RETINA CONTAINS MILLIONS OF PHOTORECEPTORS : RODES AND CONES. THEY RESPOND TO LIGHT. THE RODS ARE CONCENTRATED IN THE PERIPHERY OF RETINA. THEY ALLOW US TO SEE GRAY TONES AND THEY PROVIDE FOR OUR PERIPHERAL VISION. THE CONES ALLOW US TO SEE THE DETAILS OF OUR WORLD IN COLOUR. THEY ARE CONCENTRATED IN THE CENTRAL PART OF THE RETINA, CALLED FOVEA.

FOVEA CENTRALIS THE HUMAN FOVEA IS A SMALL 5 -DEGREE SPOT WITH HIGH CONCENTRATION OF CONES. THE CENTER OF THE FOVEA, THE FOVEOLA IS A SMALLER 0. 8 DEGREE SPOT, WITH THE HIGHEST CONCENTRATION OF CONES.

DEMANDS TO OCULOMOTOR SYSTEM HUMAN FOVEAL VISION PLACES SOME SPECIFIC DEMANDS TO OCULOMOTOR FUNCTION: THE FOVEOLA MUST BE POINTED TO THE OBJECT OF INTEREST AND THE IMAGE MUST REMAIN STILL. BOTH EYES MUST BE MOVED AT THE SAME TIME TO THE SAME DIRECTION.

VERSIONS VERSION OR CONJUGATE EYE MOVEMENT IS THE MOVEMENT OF BOTH EYES IN THE SAME TIME IN THE SAME DIRECTION.

THE EXTRAOCULAR MUSCLES

THE EXTRAOCULAR MUSCLES AND EYE MOVEMENTS

TYPES OF CONJUGATE EYE MOVEMENTS TO SHIFT GAZE MOVEMENTS TO STABILIZE THE IMAGE

THREE VISUALLY CONTROLLED SYSTEMS PRODUCE VERSIONAL EYE MOVEMENTS: SACCADIC /saccada/, SMOOTH PURSUIT, OPTOKINETIC/optokinetic nystagmus/

SACCADES PURPOSE: SHIFT THE GAZE STIMULUS: OBJECT NOT IN LINE OF SITE. MOTION: CONJUGATE RAPID. LATENCY: 200 MSEC

PURSUIT PURPOSE: STABILIZE THE IMAGE OF MOVING OBJECT STIMULUS: MOTION OF THE OBJECT MOTION: CONJUGATE SLOW AND SMOOTH LATENCY: 100 MSEC

OPTOKINETIC NYSTAGMUS /OKN/ PURPOSE: STABILIZE IMAGES DURING SUSTAINED HEAD ROTATION STIMULUS: VISUAL STIMULUS THAT MOVES CONTINUALLY IN ONE DIRECTION. LATENCY: 75 MSEC.

OPTOKINETIC DRUM

NYSTAGMUS RHYTHMIC, INVOLUNTARY EYE MOVEMENTS

NYSTAGMUS PENDULAR JERK

JERK NYSTAGMUS WITH CLEAR SLOW AND FAST PHASE. JERK NYSTAGMUS MAY BE PHYSIOLOGICAL AND PATHOLOGICAL / PERIPHERAL OR CENTRAL ORIGIN/.

JERK NYSTAGMUS

PENDULAR NYSTAGMUS WITHOUT CLEAR SLOW AND FAST PHASE. PENDULAR NYSTAGMUS IS ALWAYS PATHOLOGICAL AND OF CENTRAL ORIGIN.

PENDULAR NYSTAGMUS

VESTIBULAR EYE MOVEMENTS PURPOSE: STABILIZE IMAGES DURING HEAD MOTION STIMULUS: ANGULAR ACCELERATION OF THE HEAD MOTION: CONJUGATE SMOOTH OPPOSITE TO HEAD MOTION LATENCY: 15 MSEC

RECORDING OF THE EYE MOVEMENTS. 1. ELECTROOCULOGRAPHY 2. INFRARED VIDEOOCULOGRAPHY 3. MAGNETIC SEARCH COIL

PHYSICAL PRINCIPLES OF EYE MOVEMENTS RECORDING THE EYEBALL ACTS LIKE A SMALL BATTERY, WITH THE CORNEA HAVING A POSITIVE CHARGE WITH RESPECT TO THE RETINA. THIS CORNEORETINAL POTENTIAL REMAINS EFFECTIVELY CONSTANT AND THE VOLTAGE MEASURED BY SKIN ELECTRODES NEAR THE EYE VARIES BECAUSE THE “BATTERY” IS POINTED TO DIFFERENT DIRECTIONS AS THE EYE MOVES.

VOLTAGE MEASURED BY RECORDING EACH EYE ALONE IS DUE TO POTENTIAL PICKED UP BY THE LATERAL ELECTRODE COMPARED TO THE POTENTIAL NEAR THE NOSE.

BITEMPORAL RECORDINGS WITH ONLY THE TWO LATERAL ELECTRODES PRESENT LARGER SIGNALS

THE ELECTRODE PLACEMENT