It gives an idea about generalized depression. Point by point difference from expected value for age-related normal individuals. The greyscale gives a good tool for patient explanation about the disease per se. In glaucoma the diagnosis is never made depending on greyscale. This particular zone is more useful from neuro-ophthalmology point of view with their typical patterns. The machine according gives a colour coding to each point according to the actual perimetry results. The machine flags with “XX” sign if the reliability criteria are outside normal limit, but it don’t mean that particular HVF is of no use. Foveal threshold gives agood idea about visual acuity and two should be always compared. A printout with high false-negative values shows a typical “CLOVERLEAF PATTERN”. If patient is not responding to even at the previously determined threshold stimuli, it is known as false negative. If patients respond without even seeing the visual stimuli the machine flags the same in the false-positive column. If the patient responds to such stimuli, the machine flags the same as fixation loss. The machine gives intermittent stimulus to the previously determined BLIND SPOT, where the patient is not supposed to be responding. This area which gives us an idea about the reliability criteria. This program is used to look for advanced glaucomatous damages. The points are all aligned two degrees apart and not arranged over the horizontal and vertical meridian. This HVF testing program is more commonly used for early detection of glaucoma.ġ0-2 program measures 10 degree temporally and nasally and tests total 68 points. These are used for general screening and neurological conditions.Ģ4-2 test excludes the peripheral points of the 30-2 program except for the nasal one. The points are not arranged over the horizontal and vertical meridian. The program tests total 76 points 6 degrees apart from each other. We should also note the pupil diameter in this column, as optimum pupil diameter required to perform a good HVF test is 2.5mm to 3 mm.ģ0-2 test measures 30 degrees temporally and nasally. Patient’s date of birth is also entered in this zone, which is pretty important as the machine compares the data with the age-matched normative database. It gives us the idea about the test performed (24-2 or 30-2), the name of the patient, visual acuity, size of the stimulus. Whereas in case of severely depressed visual acuity patient’s size V stimuli are used most frequently.įor easier understanding of the HVF printouts, we would like to divide the printout into 8 segments as shown in (FIG 3) ZONE-1 The most common stimulus used is size III. SIZE OF STIMULUS - In HVF machine it is from size I to size V. The Threshold point for each retinal point can be determined by bracketing technique. THRESHOLD- it is the dimmest target perceived with 50 % probability for a fixed retinal point. 0 dB corresponds to the maximum brightness of the stimulus that can be produced by the perimeter (10,000 asb) and 51dB to the weakest intensity possible (0.08 asb).įig 2 shows the association between light intensity and retinal sensitivity. The DECIBEL (db) unit is used to denote retinal sensitivity. Stimulus Intensity- this variable and for HVF it is from maximum 10000 asb to minimum 1asb. In case of Humphrey visual field it is 31.5 apostilbs (asb) Background Luminance- the background luminance is constant for each machine. We will be discussing about how to evaluate the Humphrey visual field (HVF).īefore delving deep into the Humphrey field testing, we should know few basic points which will keep on revolving during the whole discussion. Bjerrum’s screen, Goldmann, Lister perimetry) There are mainly two types of perimetry test: Perimetry is the measurement of “Hill of Vision” in terms of establishing the patient’s differential light sensitivity. The hill is highest at fixation, where the visual sensitivity is highest and as we go peripherally the height of hill decreases due to decreasing visual sensitivity in the periphery.īased on this principle the modern visual field testings are operated. The limits of visual field for each fixing eye is 60 degrees superiorly and nasally, 75 degrees inferiorly and 110 degrees temporally.įig 1 shows the normal island of vision as described by TRAQUAIR. Visual field is the part of environment that is visible to the steadily fixing eye.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |