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Module 1: Entoptic phenomena Came from the Greek word ENT which means “within”, and Optic means the eye , phenomena which means events that are observable. This phenomenon has given early scientists to observe and study the structures of the human eye, to detect errors and understand how the human eye works. First described by Johann Purkinje in the 1800s. A.) Phenomena caused by Transparent Media source of discomfort and alarm to the patient but it does not interfere with vision.
**2. Blue Field
2.** lens - radiating streaks. - due to suture line in A phenomenon consists of seeing tiny bright spots that rapidly move in squiggly lines , 3. Physiological Halo – caused by radial arrangement of lens fibers, less bright than pathologic halo, smaller angular diameter (7- degrees) 4. Pathological Halo – caused by accumulation of mucus and debris in the corneal tear film for patients with conjunctivitis, IOP increase in glaucoma, keratopathy. **B.) Vascular and Circulatory Phenomena
- Floaters/Muscae Volitantes** Seen by the patient as small specks or dots (single round globules) that can be seen against a bright background like diffusely illuminated wall or the blue sky. especially when looking into the bright clear blue sky or an open field of snow. They are thought to be due to the movements of white cells in the capillaries near the macula. 3. Purkinje Tree Images of the retinal blood vessels. The image is very transient and can be prolonged only by setting the source light in constant motion. **C.) Phenomena Associated with Central Vision
- Haidinger's Brush** Observed when viewing a large diffusely illuminated blue field through a polarizer. Appears as a pair of yellow, brush like shapes which seems to radiate from the point of fixation. it can be used in selecting and creating Radiating lines Star like pattern
eccentric fixation. Caused by the preferential absorption of blue light by the xanthophyl pigment in the fovea.
2. Maxwell's Spot An entoptic phenomenon in which the subject can observe a dark or grayish spot in the visual field which correspond to the fovea. **D.) Phenomena Associated with Retinal Distension or other Retinal Activity
- Phosphene** horns around the point of fixation. observed by using a glowing tinder taken from a fire. 3. Photopsia/Moore's Lightning Streak Named after Moore. An entoptic phenomenon consisting of a flake of lightning. Seen most often in the temporal visual field. Sometimes accompanied by the simultaneous development of a shower of small vitreous opacities. Module 2: Pupil LESSON #1 Pupil Size Measurement A phenomenon characterized by the experience of seeing light without light entering the eye. Produced by an inadequate retinal stimulus. A dark circular spot in the visual field. Rubbing, closing, or putting pressure in the eye can activate the ganglion cells in the retina, which the brain is required to interpret as a visual signal. seeing waves of color and patterns of black and white. 2.Blue Arcs of the Retina The visual phenomenon usually referred to as "the reddish-blue arcs and the reddish-blue glow of the retina". Entoptic images influenced by the distribution of the retinal nerve fibers. It can be seen as two faint blue transient arcs bowed like a pair of normal illumination, the average adult’s pupil size measures around 3.5 mm but can range from 1.0 mm to 10 mm and decreases as one ages due to senile miosis.2 Pupils should be within 1 mm in size of each other. A fully dilated pupil is typically in the 4 to 8 millimeters in size, while a constricted pupil is in the 2 to 4 mm range. 3 Important Parts in Examining the Pupil Check for pupil size in light and dark (looking for difference in size) Check for a reaction to light in each eye. Check for a Relative Afferent Pupil Defect (RAPD)
2. Emotions Parts of the brain that help us feel and decode emotion as well as mentally focus can make pupils widen. - A study showed that when people listened to emotionally charged sounds (a baby laughing or crying) versus sounds that were considered neutral (routine office noise), their pupils became bigger. - Researchers have found that when we must think very hard because a task is difficult or new to us, our pupils dilate — and the harder the task, the more they dilate. - Most people have pupils that are only a couple of millimeters wide and symmetrical (meaning both eyes have the same size pupil). A small subset, however, naturally have one pupil that’s bigger than the other. But pupils aren’t static. - Under certain conditions — including those that are environmental, psychological, and medical — it’s completely normal for your pupils to change size, getting either smaller or bigger depending on the circumstance. You need healthy pupils to see properly. LESSON # 2 Interpupillary Distance Inter-pupillary Distance (IPD) is the distance measured in millimeters (Links to an external site.) between the centers of the pupils (Links to an external site.) of the eyes. This measurement is different from person to person and also depends on whether they are looking at near objects or far away. Monocular PD refers to the distance between each eye and the bridge of the nose which may be slightly different for each eye due to anatomical variations. METHODS: 1. ANATOMICAL METHOD reference points - centers of the pupil - temporal pupillary margin of one eye to the nasal margin of the other eye - temporal limbus of one eye to the nasal limbus of the other eye 2. PHYSIOLOGICAL / CATOPTRIC METHOD - makes use of the catoptric images (reflection of light on the cornea) - measure the distance between the corneal reflexes of the 2 eyes 3. PHOTOGRAPHIC - for patients with nystagmus
MODULE 3: Pupillary Reflex Pupillary light reflex (PLR) is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the pupil and the eye, thereby assisting in adaptation to various levels of lightness/darkness. A greater intensity of light causes the pupil to constrict (miosis/myosis) (allowing less light in), whereas a lower intensity of light causes the pupil to dilate (mydriasis, expansion) (allowing more light in). Thus, the pupillary light reflex regulates the intensity of light entering the eye. LESSON # 1 Direct and Consensual Reflex Test Indirect / Consensual Pupillary Light Response is the quantity and quality of the change in size of the pupil of one eye when light is placed on the retina of the opposite eye. Direct Pupillary Light Response is the quantity and quality of the change in the size of the pupil when light is placed on the retina of that eye. The principal censor for the pupillary light response is the photopic system (the cones); therefore, the light on the foveal area will be the main determinant of the response of the pupil. Pupillary Near Response is the quantity and quality of change in the size of the pupil when fixation is change from distance to near, or from near to distance. The pupil is the dark circular opening in the center of the iris and is where light enters the eye. By analogy with a camera, the pupil is equivalent to aperture whereas the iris is equivalent to the diaphragm. It may be helpful to consider the Pupillary reflex as an 'Iris' reflex , as the iris sphincter and dilator muscles are what can be seen responding to ambient light. Whereas the pupil is the passive opening formed by the active iris. Pupillary reflex is synonymous with pupillary response, which may be pupillary constriction or dilation.
how they respond to a light shone in one eye at a time. The test can be very useful for detecting unilateral or asymmetrical disease of the retina or optic nerve (but only optic nerve disease that occurs in front of the optic chiasm). The physiological basis of the RAPD test is that, in healthy eyes, the reaction of the pupils in the right and left eyes are linked. In other words, a bright light shone into one eye leads to an equal constriction of both pupils. When the light source is taken away, the pupils of both eyes enlarge equally. This is called the consensual light reflex. To understand how the pupils react to light, it is important to understand the light reflex pathway. This pathway has two parts. AFFERENT part of the pathway (red) refers to the nerve impulse/message sent from the pupil to the brain along the optic nerve when a light is shone in that eye. EFFERENT part of the pathway (blue) is the impulse/message that is sent from the mid- brain back to both pupils via the ciliary ganglion and the third cranial nerve (the oculomotor nerve), causing both pupils to constrict, even though only one eye is being stimulated by the light. MODULE 4 Preliminary Examinations and Confrontation Test Visual Acuity is the clarity or sharpness of vision. The visual acuity test is used to determine the smallest letters you can read on a standardized chart (Snellen chart) or a card held 20 feet (6 meters) away. Special charts are used when testing at distances shorter than 20 feet (6 meters). Some Snellen charts are video monitors showing letters or images.
**1. It is the ability to see 2 separate objects as separate.
- It is the power or the ability of the eye to see clearly and to discriminate the contours and details of an object.
- Determined by the smallest retinal image the form of which can be appreciated and is measured by the smallest object which can be clearly seen at a certain distance. Purpose:** refraction and prescribing decisions monitoring ocular health VA measurement applied to vision standards. Eye Dominance / Dominant Eye can vary from person to person. One person may have strong degree of dominance in one eye, while another person may have an eye with a lesser difference in dominance from the other eye. Cover Test differential diagnosis of HETEROPHORIA from a HETEROTROPIA. A simple, mainly objective test which is the cornerstone of the investigation of STRABISMUS.
PHORIA – Tendency of the eye to deviate. TROPIA – Actual deviation of the eye. Corneal Light Reflex Test test for strabismus in which the Px fixates at a penlight and the examiner notes the position of the reflection formed by the two corneas. Determines presence of strabismus at near and px’s fixation behavior. How is Vision determined? (Types of Visual Acuity) Measured or determined by the smallest object or line that can be seen clearly and distinguished at a certain distance. It is taken: VA - monocularly and binocularly. NORMAL - better than 20/ STANDARD/ OPTIMAL - VA is 20/ SUBSTANDARD - VA is between 20/25 to 20/ SUBNORMAL - VA is poorer than 20/ If 20/200 cannot be read: FINGER COUNTING (FC) HAND MOVEMENT AT 1M(HM) LIGHT PROJECTION WITH ACCURATE LOCALIZATION LIGHT PERCEPTION (LP/NLP) Clinical Methods Testing central vision with a standard chart Subnormal VA: patient slowly moves toward the chart until the largest letter can be read. The numerator of the Snellen fraction becomes the shortened distance, and the denominator refers to the smallest letter read on the chart. If no letters can be read at any distance, the examiner then asks the patient to Count Fingers at progressively shorter distances. If counting finger is not possible, one checks for the perception of Hand Motions, then Light Perception with Accurate Localization, Light Projection with Localization, and finally, No Light Perception. VA Notation
- English acuity 2. Metric acuity 3. Decimal acuity
- Percentage acuity 5. LogMar ENGLISH METRIC DECIMAL PERCENTAGE 20/200 6/60 .10 10% 20/100 6/30 .20 20% 20/70 6/21 .2875 28.75% 20/50 6/15 .40 40% 20/40 6/12 .50 50% 20/30 6/9 .6667 66.67% 20/25 6/7.5 .80 80%
The term tropia is used to define the direction of the strabismus (or misalignment). For example, an exotropia means that the misalignment occurs due to one eye deviating outwards. An esotropia is a deviation inwards. Vertical misalignment is also possible: hypertropia means deviated upward and hypotropia means deviated down. Note the direction: Orthophoria – no movement detected. If the eye moves inward as the follow eye is uncovered, an exophoria is present. If the eye moves outward as the fellow is uncovered, an esophoria is present. If the eye moves down as the fellow eye is uncovered a hyperphoria is present in that eye. If the eye moves up as the fellow eye is uncovered, a hypophoria is present in that eye. LESSON # 4 Corneal Light Reflex Test It is a convenient test for determining the presence of strabismus at near. A squint, or strabismus, is a condition in which the eyes do not align properly. One eye turns inwards, upwards, downwards, or outwards, while the other one focuses at one spot. can be constant or intermittent. This usually occurs because the muscles of the extraocular muscles, are not working together. As a result, both eyes are unable to look at the same spot at the same time. It can also happen because a disorder in the brain means that the eyes cannot correctly coordinate. Strabismus also makes binocular vision impossible, so it is harder for the person to appreciate depth perception. Signs and symptoms in children one of the eyes does not look straight ahead. A minor squint may be less noticeable. infants and newborns may go cross- eyed, especially if they are tired. This does not mean that they have a squint. If a child has one eye closed, or turns their head when looking at you, this could be a sign of double vision (Links to an external site.), and a possible squint. Strabismus is normally either present at birth or it develops in the first 6 months after birth. if untreated, it can lead to amblyopia (Links to an external site.), or “lazy eye,” in which the brain starts ignoring input from one of the eyes. the brain ignores one of the eyes to avoid double vision. a squint that was treated successfully in childhood returns later in adulthood. TREATMENT
- Eyeglasses or contact lenses
- Prism lenses
- Vision therapy
- Eye muscle surgery PREVENTION Strabismus cannot be prevented. Complications can be prevented if detected early enough. At the minimum children should be screened for eye health before 6 months of age and again between 3-5 years (Links to an external site.). Corneal reflex can be; If there is normal alignment, the reflection will appear in the same position in each pupil.
If there is misalignment of the eyes, the location of the corneal reflex will appear asymmetric and “off center” of the pupil in the deviating eye. The relative difference in the position of the reflex will be in the opposite direction as the eye deviation. For example, in an esotropia (where there is inward deviation of the eye), the light reflex will appear outwardly displaced from the center of the pupil; in a hypertropia (where there is an upward deviation of the eye) the light reflex will appear inferiorly displaced from the center of the pupil. The corneal reflex will be located slightly nasal (approximately .5mm) to the center of the pupil. This is because the line of sight makes a small angle (about 5 degrees) with the pupillary axis. The angle measured from the entrance pupil of the eye, is called the angle lambda. If strabismus exists , the corneal reflex will be located toward the nasal edge of the pupil (exotropia) or toward the temporal edge of the pupil (esotropia), superior (hypotropia), inferior (hypertropia). Recording: CENTRIC OR ECCENTRIC Amblyopia – another term for lazy eye. LESSON # Diplopia Test Diplopia Condition in which a single object is perceived as 2 objects rather than as one (double vision).
1. Physiologic Diplopia - A diplopia occurring in normal binocular vision for non-fixated objects whose images stimulate disparate pts on the retina outside of the panum’s area. 2. Distal Diplopia - Is the physiologic diplopia for objects beyond the point of binocular fixation.
- Proximal Diplopia - for objects nearer than point of binocular fixation Procedures:
- Look at a distant object with both eyes open.
- While fixating that object, put your index finger about 6 inches in front of your face.
- You will see two index fingers (one from the left eye's image and one from the right).
- If only one index finger is seen, suppression is present preventing the images from one eye from reaching the conscious level. Recording:
- Formation of two image: DIPLOPIA (PRESENT)
- Formation of one image: DIPLOPIA (ABSENT) MODULE 5 COLOR VISION
make a color match on an anomaloscope, a device specifically used to distinguish the various color deficiencies. The patient must adjust the ratio of red and green lights to match a yellow light in terms of hue, brightness and saturation. Type of color deficiencies MONOCHROMACY A. Monochromats have an absence of two or all three cone photopigments. 2 types:
1. ROD monochromat has no functioning photopic system. Persons with rod monochromatism generally have macular dysfunction, nystagmus, and low vision. 2. CONE monochromat has one functioning cone photopigment of the photopic system. Persons with cone monochromatism may be further characterized as red, green or blue monochromats. The red or green monochromat has reduced but adequate visual acuity while the blue monochromat has very poor visual acuity. B. Dichromats have an absolute defect or complete absence of one portion of the cone pigment system. In all dichromats there is a neutral point within the spectrum. Under photopic conditions, it is the point that appears achromatic. There is no hue present at the neutral point because it is the position where the remaining 2 photopigments are balanced. 3 types (pia = abnormality) 1. Protanopia is an abnormality of erythrolabe. There exists a major luminosity loss on the red end of the spectrum. These individuals experience color confusions or difficulty discriminating between green, yellow and red. For example, the color red is perceived as a darker color perhaps similar to brown. Finally, their spectral sensitivity shifts towards shorter wavelengths. 2. Deuteranopia is an abnormality of chlorolabe. There is a luminosity loss in the green portion of the spectrum. These individuals experience color confusions or difficulty discriminating between green, yellow and red (Fig.11.4b). Their spectral sensitivity does not shift 3. Tritanopia is an abnormality of the cyanolabe. There exists a major luminosity loss on the blue end of the spectrum (Fig.11.5b). Their spectral sensitivity shifts towards longer wavelengths. ANOMALOUS TRICHROMACY Anomalous Trichromats have a partial defect or alteration of one portion of the cone photopigment system. Anomalous Trichromacy
- Is the most common category of color blindness. It is an impairment of normal color vision, not a complete loss. * This occurs when one of the cones is altered in its spectral sensitivity. It can be red/green or blue/yellow depending on which cone is altered. * The ability of anomalous trichromats to distinguish between hues is better than dichromats but still not normal.
3 forms of Anomalous Trichromacy: 1.Protanomalous trichromacy "red - weakness"
- Any redness seen in a color by a normal observer is seen more weakly by the protanomalous viewer, both in terms of its "coloring power" (saturation, or depth of color) and its brightness.
- Red, orange, yellow, and yellow green appear somewhat shifted in hue ("hue" is just another word for "color") towards green, and all appear paler than they do to the normal observer.
- The redness component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component.
- Hence, to him the color that normals call "violet" may look only like another shade of blue.
2. Deuteranomalous Trichromacy It is a type of anomalous trichromatic vision in which the green-sensitive cones have decreased sensitivity. It is an X-linked trait, affecting about 5% of white males and 0.25% of females in the United States, and is the most common color vision deficiency. It is an inherited disorder of color vision , caused by a gene located on the X chromosome, in which a person has all three of the retinal pigments in the cones, but the sensitivity of the green-sensitive cones is decreased. A color-defective male always inherits his deficiency from his mother, who usually has normal color vision and is therefore a carrier of the defect. She may have received her color- deficiency gene from either her father (but only if he was color defective), or from her mother (who could have been a carrier herself, or rarely, who was color-defective). 3. Tritanomalous Trichromacy It is a rare type of anomalous trichromatic vision in which the third, blue-sensitive, cones have decreased sensitivity. Less than about 0.01% of people affected by it. However, it is known that reds and greens are unaffected, and some yellows may be visible on the lower end of the spectrum with this disorder.
- Plates 14 to 15 are hidden design plates with normal, not being able to see a number but color deficient.
- Plates 16 to 17 are diagnostic plates which help determine the severity of the deficiency.
- Plates 18 to 24 are tracing plates which may be used for individuals who are illiterate or children. Recording the findings: The grading criteria is defined as: Normal: < or = to 4 errors out of 17 plates Failure:
or = to 5 errors out of 17 plates
The examiner records the results by noting the # correct/total # plates followed by type of plates used. The missed plates & numbers called may also be noted to help determine the color vision defect. e.g. 7/7 OD, 7/7 OS Ishihara e.g. 12/17 OD, 11/17 OS Ishihara If possible, the type of color vision defect is determined and noted using the Score Chart provided in the lecture FARNSWORHT D COLOUR ARRANGEMENT TESTS The most common are the Farnsworth D- 15 and Farnsworth-Munsell 100 Hue. They are generally used once the pseudoisochromatic plates are failed or if the examiner would like to further qualify a color deficiency. Arrangement tests classify color vision deficits as protan, deutan or tritan, but they are unable to distinguish dichromats from anomalous trichromats. A score sheet is used to record the order of the patient’s arrangement of hues in relation to their correct sequence. Once the sequence is recorded it is then placed on an analysis graph. The color deficiency will parallel the axis of color confusion. The Farnsworth D-15 consists of 16 colored caps. The 16 different colors are selected from the Munsell system color circle. The chosen color samples are equally spaced around the Munsell system color circle. Therefore, distinction between bordering caps is quite clear to the person with normal color vision. Persons with severe color vision defects have major color confusions and will make significant arrangement errors when performing the test. Persons with mild color vision defects have minor color confusions and will generally not make significant arrangement errors when performing the test. Consequently, the Farnsworth D-15 is used to differentiate between severe color deficiencies in which the patient fails and mild to moderate color deficiencies in which the patient passes. Procedure:
- The test is performed monocularly.
- The patient is seated with caps placed 50 cm away & views the caps at a 60 degrees angle. The proper light source
- illuminates from above the test.
- The patient is to select the cap that looks the most like the fixed cap (reference cap) and place it next to it in the box. The patient then selects from the remaining caps the one that looks the closest to the
one just placed in the box and continue until all caps are in the box. There is no time limit imposed for this test.
- The examiner scores the test by recording the cap sequence on a standard recording sheet (provided in the lecture). A failure is recorded as 2 crossings on the diagram. Crossings require the caps to be placed at least 4 numbers apart. Once the graph is plotted, the examiner must determine which index line is closely parallel to the patient’s error crossing(s). OTHER CAUSES OF COLOR DEFICIENCY Other Causes of Color Vision Deficiency 1. Medications Acquired color vision deficiencies can be due to the toxicity of medications (Plaquenil, antidepressants like Prozac, oral contraceptives like Nolvadex, etc.). 2. Chronic illnesses which can lead to color blindness include Alzheimer's disease, diabetes mellitus, glaucoma, leukemia, liver disease, chronic alcoholism, macular degeneration, multiple sclerosis, Parkinson's disease, sickle cell anemia and retinitis pigmentosa. 3. Medications & Health such as antibiotics, barbiturates, anti- tuberculosis drugs, high blood pressure medications and several medications to treat nervous disorders may cause color blindness.
- Industrial or Environmental Chemicals such as carbon monoxide, carbon disulphide and some containing lead can also cause color blindness.
- Age in people over 60 years of age physical changes can occur, which might affect a person's capacity to see colors. Unlike inherited color blindness , acquired color blindness can vary over time. Symptoms may be mild and remain stable or they can be severe and progress to more serious forms of color blindness, such as monochromatism, very quickly. Often the cause of color blindness determines how severe the symptoms will be. AFTERIMAGES An After- image is a type of optical illusion in which an image continues to appear briefly even after exposure to the actual image has ended. You have probably noticed this effect a number of times. If you have ever stared for a long time at a fixed point and then suddenly shifted your gaze somewhere else, then you probably noticed a brief afterimage effect in which you continued to see the original stimulus. Learn more about what afterimages are and why they happen. Types of After Images There are two major types of after- images: positive after images and negative after- images. In some instances, the colors of the original stimulus are retained. This is known as a positive afterimage. In other cases, the colors may be reversed. This is known as a negative afterimage.
much darker than the stimulus. Glancing at the bright midday sun or the glare of bright headlights at night are two instances that might produce this type of after-image. This brief exposure to an intense source often produces a positive afteri-mage. Prolonged exposure to a colored stimulus , even if the surrounding conditions are equally well-lit. Staring at an image in a book for 60 seconds or so before turning to stare at a blank, light- colored wall can produce this type of afterimage. This prolonged exposure to a colored stimulus often results in a negative afterimage.
