3. ACKNOWLEDGEMENT:- I would like to express my sincere gratitude and thanks to Dr. Amar Agarwal (Chairman cum Managing Director) and Dr. Athiya Agarwal (Director) of DR AGARWAL EYE HOSPITAL Chennai for giving me this great opportunity to do my internship under their esteemed organization I would also like to express my special thanks to Mrs. Rekha Srivastava (HOD Of Optometrist) who helped me for providing such a good working environment in the hospital. I would also thank to all my teachers of NSHM COLLEGE OF MANGEMANT AND TECHNOLOGY and all team members of Dr. AGARAWAL EYE HOSPITAL Ltd
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6. Visual Field !!!! What is it???? Visual field is defined as that area of vision seen with open eyes. The dimensions of the field of vision are defined relative to fixation.
12. Anatomy of the RNFL Papillomacular bundle Mid-Horz. raphe Arcuate fibers Nasal fibers Optic disc
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14. At the Optic chiasm Secn of Optic N Ant knees of Willbrand Optic Chiasm Optic Tract Post Knees of Willibrand Inferio-tempo fibers Superio-tempo fibers Superio-nasal fibers Inferio-nasal fibers
15. Schematic diagram of visual pathway, including lateral geniculate nucleus (LGN), occipital lobe, and striate cortex (V1)
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17. A Scotoma is an absolute or relative area of depressed visual sensitivity surrounded by normal vision In an absolute scotoma all vision is lost In a relative scotoma a variable amount of vision remains Scotoma
18. Visual Field Changes in Glaucoma Focal damage Relative scotomas Fluctuating scotomas Absolute scotomas Paracentral scotomas (5-15 deg) Nasal steps Arcuate scotomas (Bjerrum’s scotomas) Altitudinal defects General depression in sensitivity is actually very rare in glaucoma and more indicative of cataract, miosis, or other media/refractive issues.
20. A visual field defect is defined as any departure from the normal topography of the “Hill of Vision”. Diffuse Visual field loss: Pre retinal opacities, such as corneal lesion, age related cataract and other media opacities scatter light and reduce light transmission through the eye, thereby causing a generalized reduction in the height of the “Hill of Vision”. Visual Field Contraction: Diseases which damage the peripheral retina, such as Retinitis Pigmentosa, toxic effects of some drugs, cause the circumference of the island of vision to reduce at sea-level. Visual field Defects
26. Other Field Defects Visual field loss may occur due to disease or disorders of the eye, optic nerve, or brain. In humans, confrontational testing and other forms of perimetry are used to detect and measure visual field loss. Different neurological difficulties cause characteristic forms of visual disturbances, including hemianopsias
28. In bitemporal hemianopsia vision is missing in the outer half of both the right and left visual fields. The nasal retina is responsible for carrying the information from the temporal visual field, and it goes on to cross to the other side of the brain at the optic chiasm. When there is compression at optic chias the visual impulse from both nasal retina are affected, so it leads to inability to view the temporal, or peripheral, vision. This phenomenon is known as bitemporal hemianopsia also known as tunnel vision. Bitemporal hemianopsia most commonly occurs as a result of tumors located at the mid-optic chiasm. Since the adjacent structure is the Pituitary gland, some common tumors causing compression are Pituitary adenomas, and Craniopharyngiomas Paris as seen with bitemporal hemianopsia
29. Binasal hemianopsia is the medical description of a type of partial blindness that is associated with certain lesions of the eye, and of the central nervous system, such as congenital hydrocephlus. In binasal hemianopsia vision is missing in the inner half of both the right and left visual fields. Paris as seen with binasal hemianopsia
32. We can take the following values representing intensity in apostilbs and convert them to logarithms. Plz note that higher the dB value, lower the light intensity in asb units and higher the retinal sensitivity.
33. High dB value High Retinal sensitivity It means more attenuation of light intensity stimulus which results in projecting If retinal points respond to this less intensity of light stimulus, it indicates Low intensity of light stimulus
34. Low dB value Low Retinal sensitivity It means less attenuation of light intensity stimulus which results in projecting If retinal points respond to this high intensity of light stimulus, it indicates High intensity of light stimulus
35. Threshold, Supra threshold & Infra threshold The threshold is the physiological capacity to detect a stimulus at a given location under specified conditions. If a particular intensity of light is shown 100 times and if it is appreciated 50 times and that particular intensity of light is termed as Threshold . If the stimulus intensity is seen 90% of times, it is termed as Supra threshold and if it is seen 15% of times, it is termed as Infra threshold
38. Staircase Method Stimulus Sensitivity Stimulus presentation no. 4 dB stepping 2 dB stepping Seen Points Unseen Points
39. Physiological Parameters : The parameters for most automated perimeters are loosely based on the “ Hill of Vision” where the following is taken as the usual standard of reference: • For central 5 deg low to mid 30 dB • For 5 deg to 30 deg mid to upper 20 dB • For beyond 30 deg teens to low 20 dB
40. One level supra threshold strategy In its simplest form, one level strategy, stimuli of constant luminance are presented at selected locations across the visual field. However, it is known that the Hill Of Vision declines in sensitivity with increasing eccentricity from the fovea. It is therefore, possible that a stimulus which is just supra threshold in the periphery of the visual field may result in small relative defects being missed at the fovea or vice-versa
41. Gradient-adapted threshold strategy Here the stimulus luminance is automatically modified to be brighter at more peripheral locations and dimmer centrally, the supra threshold level will take into account the normal shape of the “Hill of Vision” and the technique will yield equal sensitivity for scotoma detection across the visual field. In consequence, adapting stimulus luminance across the “Hill of Vision” is more sensitive at defect detection than One level Strategy . This approach is called a gradient adapted Supra threshold strategy and is dependent upon the knowledge of “Hill of Vision” in a standard normal observer.
42. Humphrey Automated Visual Field Tests Threshold Tests Screening Tests * Central Tests Peripheral Tests Specialty Tests Central 30-2 Central 24-2 Central 10-2 Macular progm. Peripheral 60-4 Nasal step Temporal crescent Neurological 20 Neurological 30 *Discussed on the next slide
43. Humphrey Automated Visual Field Tests Threshold Tests Screening Tests * Glaucoma [Armaly central, Armaly full field, Nasal step] [Central-40/76/80/166] Central 30 deg test Full field tests [Full field-81/120/246 ] Peripheral [Peripheral-68]
56. Stimulus duration – 200 miliseconds, shorter than the latency of involuntary eye movements (250ms), so patient will not have time to look towards the target
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60. Reading and Interpreting the Printout: Single Field Analysis 1.) FIXATION LOSSES: The Humphrey field analyzer periodically checks the patient's fixation by presenting stimuli within their blind spot (Heijl-Krakau Technique). When the number of fixation losses is greater than 20%, a symbol (XX) will appear next to the fixation losses to alert the doctor there is reason for concern. 2.) FALSE NEGATIVE ERRORS: A brighter stimulus is presented at a test point in the field that was earlier reported, as being seen, having "Normal Sensitivity" but now the patient does not respond to the bright stimulus. High, false negative scores might indicate fatigue or inattentive patient. 3.) FALSE POSITIVE ERRORS: The projector makes a noise when it moves and the patient responds to the sound though no stimulus has been presented. The patient is responding to outside factors or trying to out guess when the stimulus will be presented. A high false positive score indicates that the patient is "Trigger Happy.
63. Fluctuating Factors 1.)Short-Term: Relative normality is less than 3dB when the same point is tested twice and is usually between 1dB and 2dB during a given test period . There are two reasons for an abnormal Short-Term Fluctuation (SF), inattentive patient or a patient with a diseased visual system. LOW FLUCTUATION: < 1.5 dB NORMAL FLUCTUATION 1.5dB TO 2 dB MEDIUM FLUCTUATION >2 dB BUT < 3 dB HIGH FLUCTUATION >3 dB 2.) Grayscale - Is for the patients benefit; for their interpretation or understanding. Represents tested points and non-tested intermediate points , which have been assigned values, interpolated from surrounding points. It tells the doctor nothing about the depth of a scotoma. 3.) Total Deviation - These numeric values represents the difference in decibels between the patient's test results and the expected age-corrected normal values at each test point in the visual field. The plot just below this finding are graytone (symbols) which shows the statistical significance for a given test value. These are based on the deviation from expected normal patient threshold profiles. The darker the pattern (symbol) the more significant the deviation from the expected threshold 4.) Pattern Deviation - This plot is similar to the Total Deviation except the STATPAC attempts to adjust the analysis of the test results for any overall changes in the height of the measured hill of vision caused by say cloudy media , cataracts or small pupils . Hence, this numeric pattern deviation plot shows the deviation in decibels from the age-corrected normal values, adjusted for any shifts in overall sensitivity. The plot just below this finding are again graytone (symbols) which show the statistical significance of the results at each point. The darker the pattern (symbol) the more significant the deviation from the expected threshold. 5.) Probability of Abnormality - The P value represents the probability whereto a patients findings have deviated from the expected normal values. The probability statements is based on the Hill Of Vision distribution seen in the normal population. This P value is computed from the total deviation and the pattern deviation plots. P<1% means that this deviation happens in less than 1% of the normal population and must be consider highly suspicious.
64. Global Indices 1.) Mean Deviation or Defect (MD) - The (MD) is the mean difference in decibels between the "normal" expected hill of vision and the patient's hill of vision. if the deviation is significantly outside the norms, a P value will be given. Example: P< 0.5% means that less than 0.5% of the normal population showed a (MD) larger than the value found for this test. This index is a measure of overall depression, elevation of the field or significantly deep losses in one part of the field and not in others. 2.) Pattern Standard Deviation (PSD) - This is a measurement of the degree which the shape of the patient's measured field or hill of vision departs from the "NORMAL" age-corrected reference field model. The value is expressed in decibels and any value of 2dB or greater will have a (P) value next to it indicating the significance of the deviation. 3.) Short-Term Fluctuation (SF) - This is what the Field Analyzer has been testing all along. It is simply an index of the consistency of the patients responses during the field testing. This value is obtained when ten (10) pre-selected points are tested twice and the difference, in decibels, of the patient's responses are compared. 4.) Corrected Pattern Standard Deviation (CPSD) This is a calculated measurement in decibels of how much the total shape of the patient's hill of vision deviates from the shape of the "NORMAL" hill of vision for the patient's age, after being corrected for intra-test variability. In calculating the (CPSD) the STATPAC attempts to determine if the irregularities in the hill of vision are real by removing the short-term fluctuation (SF), which may mask a relative scotoma .
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69. With severe glaucoma it is displayed severe visual field loss on 24-2.Fixation appears to split from above Pts are 3° apart from the pt of fixn
70. 10-2 allows better evaluation of juxtafoveal area Pts are 1.2° apart from the pt of fixn
71. FASTPAC is used when SITA is not available and when the patient is showing fatigue-artifacts
72. as of ’91 showing overall depression Still showing marked fatigue artifact Almost normal VF with few scatterred dep pts
73. Inf NeuroRetinal Rim thinning 18mins 25secs 7mins 54secs Overall constriction of VF Superior arcuate defect correlating with disc findings
76. Glaucoma Hemifield Test • In glaucoma, the upper and lower hemispheres of the field are often significantly different. •• Points within the visual field are grouped together into 5 smaller zones with mirror images of one another above and below the horizontal meridian. Probability values are used rather that threshold values. The mirror images are compared to one another. There are 5 possible interpretations of the results that are printed.
77. GHT Indicators 1. GHT outside normal limits: if the difference between the mirror image zones would be expected in less than 1% of the normal age-matched population, this message will appear. 2. GHT borderline: The same as above except that for the comparison between zones, the probability only has to be at the 3% level and the pair at the 1% level. 3. General reduction of sensitivity: Here the criteria for a localized depression are absent and the general height adjustment yields a result in which the best part of the field is depressed to a degree that would be expected in less than 0.5% of the age-matched population. 4. Abnormally high sensitivity: If the patient's threshold values are higher than those occurring in less than 0.5% of age-matched normals, this message will appear. The best part of the field is more sensitive than that of 99.5% of the normal age-matched population. This will supersede all other messages and indicates that the patient's responses are unreliable. 5. Within normal limits: None of the above criteria are met
78. Diagnosing Glaucoma with Visual Fields: (Anderson Criteria) · GHT outside normal limits on 2 consecutive fields · Cluster of 3 or more non-edge points on the pattern defect at p < 5% with 1 point at p < 1% over 2 consecutive fields · CPSD < 5% over 2 consecutive fields · Moderate loss defined as MD between 6 and 12 dB · Severe loss defined as > 12 dB defect on MD · A value of “0” within the central 5% of fixation is considered severe
79. These are modified bar graphs of threshold values. The differences between the expected and measured values are calculated and ranked. The box represents the range of deviation for the middle 70% of stimulus locations, i.e. the standard deviation.The upper tail represents the range of 15% best stimulus locations and the lower tail the range of 15% worst stimulus locations. Serial Field Analysis (Box Plotting)
80. 1.) Overall shape of the box, how elongated or compact it is. 2.) The location of the three dark lines inside the box that indicate the median. 3.) The length of the upper and the lower tail. 4.) Length of the box proper. 5.) The top and bottom end points of a line along which a box lies. 6.) The position of the box plot in relation to decibel scale. Interpretation of Box Plotting
81. · Artifacts · Trial lens rim artifacts · Eyelids and brows · Refraction scotoma · Wrong fixation target · Dim light bulb · Inexperienced perimetrist · Inexperienced patient and learning curve · Cataract progression · Long-term fluctuation Challenges to Interpretation:
Trigger happy patient – believes that he must push the button veryu quickly, may be even during the 0.2 sec interval while the light is still on.he needs to know that the machine waits for a time to receive a response after the brief stimulus.
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