Visual field
- 1. Visual field
- 2. Definition The visual field refers to the total area in which object can seen in the side vision while you focus your eyes on a central point
- 3. Hill of vision • Hill of vision is a 3D graph of visual sensitivity. • The peak corresponds to fixation where visual sensitivity is greater and height of hill of vision decrease towards periphery that is the central fovea will have maximum vision and periphary will have less vision.
- 4. Normal limits • 60°superiorly • 60°nasally • 75°inferiorly • 100°temporally • The macula corresponds to the central 13°of the visual field.The fovea to the central 3° of visual field
- 5. Examination of the visual field 1) Confrontation test : In confrontation procedure examiner sits opposite or confronts the patient and is concerned mainly detecting restrictions in the outer limits of visual field. Procedure: • Patient should have his/her back to the light and should face examiner at distance of about 1m. • Uniform dark background should be present behind the examiner • Patient uses the examiner open eye as a fixation target. • With the patient fixating examiner eye the test object is moved inward from periphary in an arc stimulating the curve of imaginary perimeter
- 6. • Patient is instructed to rotate their eyes to fixate the moving object but they should not move their head to follow the target. • The patient is asked to report when he/she first see the object. • This test is usually done in 8 half meridian that is 0,45,90,125,180,225,270,and 315.
- 7. 2)Tangent screen: Tangent Screens are used to develop a map of a patient’s visual field. This map can then be used to diagnose various disease conditions of the eye including ocular hysteria, eye-lid droop. These instructions are intended to describe examination of the patient and not the diagnostic part of the testing process. Procedure : • The tangent screen is a flat,usually black surface used to measure central 30°of visual field • The bjerrum screen is made of black matte material and stiched with radial lines at 15°intervals and circles at 5°intervals. • The patient is seated in a manner that positions the eyes one meter from the screen and such that they are at eye level with the center of the tangent screen target. The lights are dimmed and one eye is occluded. • The patient is instructed to maintain gaze on the white button in the center of the screen.
- 8. • Starting with the top center radian, the examiner makes the object appear and moves it slowly towards the center. The object should not be more than 1-2 inches from the screen but it is recommended that the object do not touch the screen to avoid damaging the felt screen. • The patient is asked to report when the object disappears . At the specific point where the object disappears, a black pin is inserted into the screen to mark that point. The examiner continues to move the object slowly towards the center and the patient is asked to report when the object re- appears. At the specific point where the object re-appears, a black pin is inserted into the screen to mark that point. • The process continues all the way to the lower extremity of the radian with the patient indicating appearance (or disappearance) of the object on that radian.
- 10. 3)Amsler chart: • It was designed by marc amsler • The grid chart evaluates the central 10°visual field • It is a diagnostic tool that is used mainly in screening detection and monitoring macular diseases Procedure : • Each chart has an overall size of 10cm vertically and horizontally and each small square measures 5mm in each direction • When viewed at a distance of 28-30cm,the entire chart subtend an angle of 1 degree There are 7types of amsler chart:
- 11. 1. Chart-1: • It is commonly used.It comprises a high contrast white grid on a black background. • This is arranged in 20 horizontal and 20 vertical rows making 20 square each • Used in relative and absolute scotoma
- 12. 2. Chart 2: • It is similar to chart 1 but has diagonal lines. • Used for patient having central scotoma. • Patient is asked to look where two line would cross.
- 13. 3. Chart -3: • It is a red grid on black background • Used to investigate scotoma for colour • This chart can also be used to differentiate patient with functional vision loss as from malingering with the conjunction of red- green lenses. • The red grid may allow detection of artificial monocular field /vision loss.
- 14. 4. Chart -4: • Has white dot on black background • Designed detect scotomas only • This chart does not has line to distort instead it consist of small white dots randomly distributed over a blackground.
- 15. 5. Chart -5: • has white parallel lines on the black background • Lines are oriented horizontally to detect metamorphopsia resulting from retinal and choroidal disorders • This design make the chart to rotate the chart to any meridian to check for irregularities in particular area.
- 16. 6. Chart – 6: • Has black parallel lines an white background • To detect metamorphoria • Central lines are close together enclosing more detailed evaluation
- 17. 7. Chart -7: • Similar to chart 1 but contain smaller squares in central 8° • Mainly suitable for vision disturbance from macular disease,especially early is the course of disease
- 18. Perimetry :Perimetry is the systematic measurement of visual field function. a) Static perimetry: • Static perimetry tests different locations through out the field at a time. • First a dim light is presented at a particular location • If the patient does not see the light it is made gradually brighter until it is seen • This procedure is then repeated at several other locations until the entire visual field is tested.
- 19. b) Kinetic perimetry: • Kinetic perimetry uses mobile stimulus moved by an examiner such as in goldmann kinetic perimetry • Single test light of constant size and brightness is used • The test light is moved towards the centre of vision from the periphery until it is first detected by the patient • This is repeated by approaching the centre of vision from different directions • This procedure is repeated using different test light that are larger or brighter than the original test light • It is useful for mapping visual field sensitivity boundaries.
- 20. HFA • The process of measuring the visual field is known as perimetry, which involves the mapping of the visual field using a perimeter. • This is an instrument that enables the projection of a known visual stimulus at a fixed distance from the eye within a bowl of calibrated luminance.
- 21. • Humphrey field analyser is based on the Swedish Interactive Threshold Algorithm (SITA). • The tests 10-2, 24-2, 30-2 can be performed in either SITA-Fast or SITA-Standard. SITA-Fast is a quicker method of testing. It produces similar results compared to SITA-Standard. • It tests the visual field monocularly with a testing distance of 30cm. • The result of the analyser identify the type of visual field defect. • It provides information regarding the location of any disease or lesions in the visual field.
- 22. RELIABILITY INDICES There are several reliability indices that are commonly used to give guidance regarding a patients performance. • These include : 1. FIXATION LOSS 2. FALSE POSITIVE 3. FALSE NEGATIVE
- 23. 1). FIXATION LOSSES (FL) : • The fixation loss rate provides an estimation of how steadily an eye fixates during a visual field test. • It is recorded when the patient responds to a stimulus that is projected on to area of there blind spot. • If the patient responds positively to the stimulus, it is assumed that the patient wasn’t fixating appropriately. • Fixation losses are flagged frequently when the blind spot has not been mapped accurately. • Fixation loss should not exceed more than 30% .
- 24. • GAZE TRACKER : • Gaze tracker monitors eye fixation through out the visual field test . • It is displayed as a bar chart on the monitor and the print out. • Upward deflections indicate eye movements and downward deflections are recorded when the position of the eye cannot be determined or when there was a blink.
- 25. 2. FALSE POSITIVE: • It is indicates a “trigger happy” patient who is responding when no stimulus is presented. • It is evaluated either by monitoring for responses when one is not expected or by going through the process of preventing a target and having the patient respond to the sound when no target is actually presented. • Normally false positive should be less than 15% if false positive is greater than 33% the result should be discarded and the field test is repeated. • Other indications include :- high mean sensitivity, white areas on the grey scale print out and larger defects on the pattern deviation plot than the total deviation plot.
- 26. 3. FALSE NEGATIVE : • False negative errors recorded when the patient fails to respond to brighter stimulus (9dB). • It should be less than 20% • High false negative scores indicates that the patient is fatigued, in attentive, malingerer, or has genuine significant visual field loss and also in glaucoma patients.
- 28. SINGLE FIELD ANALYSIS • The HFA single field analyses is designed to assist in the interpretations and identification of visual field defects . • Along with the patients demographic data and reliability parameters , • It includes: The sensitivity level for each location in dB. Grey scale display . Global indices. Glaucoma hemifield test. Total deviation in dB. Pattern deviation in dB.
- 29. 1) NUMERICAL DISPLAY: • It represents raw values of patient’s retinal sensitivities at specific retinal points in dB. • Higher numbers equate to higher retinal sensitivities . • Sensitivity is greater in the central field and decreases towards the periphery . • Normal values are approximately 30dB. 2) GREY SCALE: • A graphical representation of the numerical display allowing for easy interpretation of the visual field loss . • Low sensitivities are indicated by the dark area and higher sensitivities are represented with a lighter tone. • This scale is used to demonstrate vision changes to the patient but not used for diagnostic purpose.
- 31. GLOBAL INDICES 1) MEAN DEVIATION It is a measure of average sensitivity. It is useful to monitor the overall change in the visual field. It is derived from the total deviation . A negative value indicates field loss while a positive value indicates that the field is above average. p value is given if the global indices is abnormal. Eg: p<2% , it means less than 2% of the population has a vision loss worse than measured.
- 32. 2) PATTERN STANDARD DEVIATION; • It is derived from pattern deviation. • It highlights only focal loss. • It is a measure of the non-uniformity in the shape of the hill of vision. 3) SHORT TERM FLUCTUATIONS • It is a measure of the intra test variance. • It has to be a little clinical value. • It is not calculated when using SITA.
- 33. 1) TOTAL DEVIATION : • It compares the result with an age related normal population at specific retinal points. • Negative values indicate lower than normal sensitivity. Positive values indicate higher sensitivity. And zero indicate no change. • The normal range is greatest in the periphery than centrally. 2) PROBABILITY DISPLAY • It provides the statistical display that demonstrates the percentage of normal population who measures below the patient’s value at specific retinal point.
- 34. GLAUCOMA HEMIFIELD TEST • It provides assessment of the visual field where glaucomatous damage is often seen. • It compares five corresponding and mirrored areas in the superior and inferior visual fields. • The visual field result can be:- Outside normal limits: significant difference in superior and inferior fields. Borderline: suspicious difference. Within normal limits: no difference.
- 37. When to perform? • Patients with central vision loss, non refractive reduced vision , scotoma. • Glaucoma • Neurological disease:- headache, tingling and numbness of limbs. • Retinal disease:- macular degeneration • A risk of developing drug related retinopathy
- 38. Evaluation of visual field 1) Instrument variables stimulus size stimulus duration stimulus color 2) Patient variables learning fatigue pupil size refractive error media opacities age
- 39. thank you