Color Vision and Color Blindness

Color Vision & Color Blindness •Colour perception by the eye is due to: two receptors present in the layers of retina : 1. RODS (Scotopic Vision) 2. CONES (Photopic Vision) 3 types of cones with 3photosensitive different photosensitive pigments: •(These cells contain pigments.) 1. Red Sensitive Cone Pigment 570nn 2. Green Sensitive Cone Pigment 535 nm 3. Blue Sensitive Cone Pigment 445 nm 70 2 main types of Color Vision deficiency • Red-Green deficiency people are unable to distinguish certain shades of red and green; it is the most commonly inherited type. The gene coding for the pigment protein of red and green cones is located on the X chromosome; that is why this condition is more frequent among men. Blue-Yellow deficiency a rare condition where it is difficult to distinguish between blue & yellow. The gene of the blue cone pigment is on chromosome 7 . 71 Trichromats  There is all 3 types of pigments.  All the people with normal color vision are Trichromats  but in abnormal Trichromats : One of the three cone types is anomalous. poorer discrimination in some colors: (3 colors are required to match any other) Protanomalous = anomalous L cones 1% (m) : decreased ability to see red Deuteranomalous = anomalous M cones Tritanomalous 5%(m): decreased ability to see green = incidence unknown: decreased ability to see blue Dichromats  One of the three cone types is missing  Only need two colours to match any other : Sees a much reduced range of colours Protanope = lacks red cones 1% (male): do not see RED Deuteranope = lacks green cones Tritanope = lacks blue cone 1% (male): do not see GREEN 0.002%(very rare): do not see BLUE Prot (first):Red= the most frequency of blindness Deuter (second) :Green blindness Trit (third): Blue blindness Protanopes: do not see RED Deutranopes: do not see GREEN Tritanopes: do not see either BLUE Monochromats  Cones do not function (all cones or 2 of them)  : No colour vision : total color blind  No colour matched with any other.  Scotopic vision: (instead of photopic vision) (Have B & W vision due to rods only). Ishihara plate test Various tests have been developed to identify colour blindness. • The most common used for routine colour vision screening in schools/ medicals. • It’s the test for red/green colour blindness, but not blue colour blindness. •It Contains 24 plates of circles created by irregular colored dots (in two or more colors).  each figure would be recognized within 3 sec or less.  The plates are designed to be used in adequate daylight conditions  The plates should be held 75cm from the subject and the plane of the plate is at right angles to the line of vision. Analysis The Results If 13 (out of 24) or more plates are read normally, the color vision is regarded as normal. If only 9 or less than 9 plates are read normally, the color vision is regarded as deficient. 77 Plate 1 Both normal and those with all color vision deficiencies should read the number 12. Plate 2 Those with normal color vision should read the number 8. Those with red-green color vision deficiencies should read the number 3. Total color blindness should not be able to read any numeral. Neurological examinations 1. Cranial nerve examination 2. Stretch reflexes 79 80 Assessment of cranial nerve lll :Oculomotor Pupillary Reflexes: 1.Accommodation reflex 2.Light reflex Accommodation reflex Look at that mark on the wall, now look at my finger” Examine the pupils for size, shape, equality and regularity. 2 parts : a) convergence reflex : convergence of the pupils b) pupillary accommodation reflex: contraction of pupil on accommodation: pupil contracts while looking at near object  Mydriatic: Unilateral dilated pupil : drugs- cocaine, eye drops Light reflex When light is shown to one eye: Both pupils constrict Put your hand in between the patient’s eyes . With a pocket torch, shine the light from the side. Direct light reflex: throw light into the eye, look for pupillary constriction in the same eye:  Normally, the pupil into which the light is shone constricts rapidly. Consensual light reflex: keep an obstruction between the two eyes. look for constriction in other eye: way Simultaneously the other pupil constricts in the same Examination of Vestibulo-Cochlear Nerve (CN VIII)  Hearing + Balance (by using a tuning fork).  tuning fork (Diapason): acoustic resonator (512Hz)  It resonates when it’s vibrating by striking it against a surface. determine the conductive & sensori-neural hearing loss. 1. Weber Test 2. Rinne test 83 Rinne test : to compares time of air and bone conduction 1. Place the base of the tuning fork on the client’s mastoid process 2. If it is heard. hold it until the sound disappears. 3. As soon as the subject indicates the disappearance of the sound, move the fork in front the external auditory meatus (1-2 cm) 4. If the subject hears the sound, the ear is probably normal and if not the subject probably has conduction deafness. 84 1. Conductive deafness (in the middle & outer ear) : something is preventing air transmission through the external auditory canal, or the oval window.: Wax or cerumen in the external canal / canal/ Foreign body in ear canal/ Infection in the outer ear. 2. Sensorineural deafness (caused by damage to the cochlea, organ of Corti, or to 8th nerve, or its central connections). 85  Rinne-positive (The normal ear): AC is better than BC The tuning fork should be heard when presented at the external auditory meatus  Rinne negative (Abnormal): Bone conduction better than air conduction = =conductive deafness: no sound is audible at the external meatus Weber Test A vibrating tuning fork is placed on the forehead Center . Normally the sound is heard in the Center of the forehead.  The tuning fork should be heard equally in both ears  conductive deafness the sound is heard louder in the abnormal ear.( with obstruction to the passage of sound)  nerve deafness (a sensorineural hearing loss ): the sound is transmitted better to the normal ear. 87 Gag reflex Examination  use a soft cotton swab to tickle the back of the throat on both sides. This should cause the person to gag (swallow) . ◦ It is a normal defense mechanism that prevents foreign bodies from entering the trachea, pharynx, or larynx  the sensory limb: back of the tongue and the throat: by CN IX (Glossopharyngeal)  the motor limbs: the soft palate and bilateral contraction of pharyngeal muscles : The brief elevation of them: by CN X(Vagus Nerve) 88 2) Stretch reflexes Normal reflexes depend on normal function in the nervous system  A reflex is an automatic, involuntary response to a stimulus . necessary to survival. (maintain homeostasis) Removes body from painful stimuli that could cause tissue damage. Prevents body from suddenly falling and moving. Components of a Reflex Arc 1) Sensory receptor 2) Sensory neuron. 3) Spinal cord or brain tissue 4) Motor neuron 5) Effector organ/tissue –responds to the message from the motor neuron. Examination of the reflexes  Use the flat or sharp end of the reflex hammer to quick tap 1. Tap the tendon with a Reflex Hammer, it causes muscle to stretch 2. That it stimulates specialized sensory receptors (muscle spindles) to be stretched. 3. conduct stimulation message towards spinal cord through a sensory nerve. 4. The motor neuron will synapse with the muscles , results in muscle contraction. Achilles Reflex (Ankle-jerk Reflex ) Stimulus: Tap to tendon Response: extension at ankle (plantar flexion) Have client sit on a chair/table, so that both feet hang over; -Dorsiflex the foot at the ankle. -Strike the Achilles tendon. Patellar (knee-jerk) reflex Stimulus: tap to patellar tendon Response: extension at knee Spinal Segment: L2-L4 Have your partner sit on a chair. both feet hang over the edge. Locate the patellar tendon of the leg and tap it with the hammer Biceps Reflex Stimulus: tap to biceps tendon. Response: Flexion at the forearm & contraction of the biceps . 1. Have your partner rest their arm on a table with the palm facing up (supinated position) & arm should be partially flexed. 2. Press slightly your thumb on the biceps tendon 3. Hit your thumbnail with the hammer Triceps reflex Stimulus: Tap to tendon of triceps brachial muscle Response: Extension of lower arm & contraction of the triceps Brachioradialis reflex Have the patient rest the forearm. -Strike the radius about 1-2 inches above the wrist. (The flat end of hammer) -Watch for flexion and supination of the forearm The Babinski reflex (Plantar reflex) Using the handle of the hammer stroke the underside of the foot with a blunt instrument such as a key. (using an upward motion from heel to toes) Normal response: planter flexion  Extension of the great toe (up going toe; positive Babinski) : abnormal : Lesion in extrapyramidal pathways. “Babinski sign (negative B) is normal in the infant and may be present for the first year of life because of the incomplete myelination of the corticospinal tract 96  Sometimes you can’t observe a good reflex :  it’s probably your “patient” is nervous and not fully relaxed: use the technique called Jendrassik maneuver: flexes both sets of fingers into a hook-like form, and interlocks those sets of fingers together. be used to distract patients when performing the tests  It is important to make sure you’re actually causing sufficient stretch of the tendon to elicit the reflex response, so  You must Strike the hammer hard enough , but swing it. An absent reflex (Hyporeflexia) can be detected in lower motoneuron lesion, or hypothyroidism can also produce this. An overactive reflex (hyper-reflexia )can result from upper motor neurons lesion & hyperthyroidism 97 Spirometry A non-invasive & simple   method for evaluation of pulmonary function. measuring lung function, specifically the measurement of the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. It help diagnosis of disease along with history, physical examination. 98 Lung volumes TV : Tidal volume: The volume of air inhaled & exhaled at each breath during normal quiet breathing IRV: Inspiratory Reserve Volume: The maximum amount of air that can be inhaled after a normal inhalation. ERV: Expiratory Reserve Volume :The volume of air that can be forcefully expired (exhale) following a normal expiration RV: Residual Volume : The volume of air remaining in the lungs after a forceful expiration. 99 Main Lung capacities Capacity: the sum of the some basic lung volumes Total Lung Capacity: TLC The volume of air contained in the lungs at the end of a maximal inspiration. TLC= RV+IRV+TV+ERV= 5800 cc Vital Capacity :VC The maximum amount of air that can be exhaled after the fullest inspiration possible( after a maximal inspiration) VC= IRV+TV+ERV = TLC – RV Inspiratory Capacity ( IC ) : The maximum volume of air that can be inspired after a normal expiration : TV+IRV Functional Residual Capacity: FRC The volume of air remaining in the lung at the end of a normal expiration.= RV+ERV 100 Spirometry Parameters Forced Vital Capacity(FVC) The maximal amount of air that can be exhaled forcefully , after a maximal inspiration . The forced expiratory breathing maneuver requires muscular effort.  Ask the subject to inhale as much air as possible . Ask the subject to expel air as much as rapidly as possible. ◦ Peak Expiratory Flow Rate : Use peak expiratory flow meter. Ask the subject to take a deep inspiration and expel as fast possible through the peak flow meter. 101 • Forced Expiratory Volume in One Second (FEV1) The volume of air exhaled during the first second of a forced expiratory maneuver. (3L) With normal lungs and airways you can normally blow out most of the air from your lungs within one second. FEV1/FVC % =75–80% (in healthy adults) FEV1 that Expressed as a Percentage of the Forced Vital Capacity ◦ The value expresses the FEV1 as a percent of the total volume of air that is exhaled. 102 103 Normal spirogram: Volume / time Volume (L) 8 Man 176 cm 76 kg 6 FVC 4 FEV1 2 5 10 Time (s) 15 Restrictive Disease: Fibrosis, Sarcoidosis, Muscular diseases Makes it more difficult to get air in to the lungs.: They “restrict” inspiration. FVC are both reduced, FEV1/FVC % may be increased Obstructive Disease: Asthma, Emphysema. Make it more difficult to get air out of the lungs. FEV1 is diminished (increased airway resistance to expiratory flow) the FVC may be increased : reduced FEV1/FVC % 107 FEF 25-75% =MMEF The mean expiratory flow during the middle half of the FVC MMEF, for maximal mid-expiratory flow). Forced Expiratory Flow This is the average flow of air coming out of the lung during the middle portion of the expiration .  In small airway diseases such as asthma this value will be reduced, perhaps <65% of expected value.    Peak expirotory flow 111