Ординатура / Офтальмология / Английские материалы / A Visual Field Evaluation with Automated Devices 2nd edition_Reddy_2006

CLASSIFICATION OF VISUAL FIELD PRINTOUTS 71

HUMPHREY VISUAL FIELD TEST PRINTOUTS

WITHOUT STATPAC ANALYSIS

So far, we have discussed Humphrey visual field test printouts with STATPAC analysis. Now we will be discussing the Humphrey visual field printouts without STATPAC analysis. They are as follows: 1) visual field testing with stimulus Size V, 2) Macular program printout and 3) Nasal step printout

FIGURE 3.31

In three-in-one printout, we will have

1.Gray scale

2.Raw data

3.Defect depth plot (The defect depth is the difference between the expected threshold value and

measured threshold value).

The numbers which appear outside each quadrant of the numeric grid are called “Quad Totals” and represent a summation of the threshold values determined in each Quadrant. These numbers which even in normals will not be the same in each quadrant, can be useful in comparing several tests on the same patient over time. These numbers are helpful in absence of statistical assistance.

CLASSIFICATION OF VISUAL FIELD PRINTOUTS 73

THREE -IN- ONE PRINTOUT MACULA THRESHOLD TEST

SITA strategies are not available to the macula threshold test. So, they have to be tested with full threshold or FASTPAC strategies.

Because of lack of normative data to the tests conducted with macular program point pattern STATPAC can not analyse the raw data of these tests. So we don’t see total deviation plots, pattern deviation plots, global indices and GHT analysis in the printout formats. STATPAC analysis is not required to the macular threshold test because we conduct this test in advanced cases of glaucoma. That is why normative data is not stored for macular threshold tests.

FIGURE 3.33

In three-in-one printout, we will have

1.Gray scale

2.Raw data

3.Defect depth plot (The defect depth is the difference between the expected threshold value and measured threshold value.

The numbers which appear outside each quadrant of the numeric grid are called “Quad Totals” and represent a summation of the threshold values determined in each Quadrant. These numbers which even in normals will not be the same in each quadrant, can be useful in comparing several tests on the same patient over time. These numbers are helpful in absence of statistical assistance.

Interpretation4 of Single Field

Analysis Printout

INTERPRETATION OF SINGLE FIELD ANALYSIS PRINTOUT 75

Step 1: Verify whether the patient data and the test data are properly fed to the field analyzer by the technician. This information fed to the field analyzer should be like that exactly given in the order form for visual field testing.

Step 2: Decide whether the test is reliability or not and the selection of test is proper or not.

WHEN WE SAY THE TEST IS NOT RELIABILITY

Step 3: The measured foveal sensitivity correlates with visual acuity, it indicates the refractive error correction for near vision is correct.

Step 4: Importance of location of blind spot. Confirm the normal position of the blind spot. (See Page no. 38)

Step 5: Analysis of total deviation probability plot and pattern deviation probability plot and their correlation with mean deviation index, pattern standard deviation and GHT analysis.

During the analysis of total deviation and pattern deviation probability plots usually we encounter the following situations.

1.Localized defect in the total deviation probability plot and almost similiar defect in the pattern deviation probability plot. We see this type of defects in pure cases of early glaucomatous optic nerve damage and retinal pathology.

2.Generalized defect in the total deviation probability plot and localized defect in the pattern deviation probability plot. We see this type of defects in irregular generalized field defects produced by cases of cataract associated with glaucoma.

3.Generalized defect in the total deviation probability plot and no defect in the pattern deviation probability plot. we see this type of defects in media opacities—cataract, small pupil, refractive errors, advanced glaucoma and optic neuritis.

INTERPRETATION OF SINGLE FIELD ANALYSIS PRINTOUT 77

Generalized defect in the total deviation probability plot and localized defect in the pattern deviation probability plot as shown in the following examples.

FIGURE 4.3

FIGURE 4.4

When the TDPP is showing generalized depression and pattern deviation probability plot is showing a localized defect, it indicates that the loss of retinal sensitivity is irregular in nature. The mild to moderate defects are eliminated and the deep defects are highlighted in the pattern deviation probability plot. In the situation we will have high MD value and high PSD value. GHT: Outside normal limits. This type of defects are usually seen in combined cases of cataract and glaucoma.

INTERPRETATION OF SINGLE FIELD ANALYSIS PRINTOUT 79

LOCALIZED FIELD DEFECT - (BOTH THE PROBABILITY PLOTS LOOK SIMILAR - WHY?)

When there is a localized field defect the total deviation probability plot and the pattern deviation probability plot almost look alike. From this we understand that there is no change in the numerical values of total deviation numerical plot when it is converted to pattern deviation numerical plot by the addition of the threshold value that converts the seventh best retinal sensitivity point of TDNP to 0 deviation. This is only possible when the threshold value that converts the total deviation numerical plot to pattern deviation numerical plot should be either 0 or very small numerical value. So by adding this minimal value to all the points in TDNP. There will not be much change in their deviation values and hence their P values of PDNP.

1. In this case the retinal sensitivity values of TDNP are varying from 2 to -29 dB.

2. The 7th best retinal sensitivity point in TDNP - (+1).

3. The threshold value that converts the seventh best retinal sensitivity value to 0 deviation is added to all the points in the total deviation numerical plot to convert it to pattern deviation numerical plot is (-1).

4. To convert total deviation numerical plot to pattern deviation numerical plot, -1 dB is added to all the deviation values of the total deviation numerical plot. So the measured retinal sensitivity at each point is changed by -1 dB only, in the pattern deviation numerical plot. Because there is no significant change in the deviation values of pattern deviation numerical plot from the deviation values of total deviation

FIGURE 4.7 numerical plot, their probability plots look similar.

When there is a localized field defect the some part of retina is normal. So the seventh best retinal sensitivity value in the total deviation numerical plot is either 0 or minimal deviation from normal. So to make the seventh best retinal sensitivity in TDNP to 0 or normal, the threshold value needed is almost negligible. When this minimal threshold value is added to all the values in the total deviation numerical plot almost similar numerical values appear in the pattern deviation numerical plot. This is the reason why the numerical values of both total deviation and pattern deviation are similar and so the probability plots also look similar.

Actually the pattern deviation plots are created to highlight the localized scotomas masked by generalized depression. When a localized scotoma is already seen in total deviation probability plot there is no need to see the pattern deviation probability plot. Even if you see, it will be similar to total deviation probability plot. Why they look alike is already discussed.

Only when there is generalized depression in total deviation probability plot, we see the pattern deviation probability plot to know whether there are any localized field defects masked by generalized depression. When there is a localized scotoma in the total deviation probability plot, there is no need to see the pattern deviation probability plot.