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1. Three or more non-edge points in the pattern deviation plot with sensitivity reduce to level of p < 5% or worse, with at least one point <1%

2. Glaucoma hemifield test is outside normal limits. 3 Corrected pattern standard deviation p <5%

Criteria should be fulfilled on at least two occasions

Non-characteristic visual field defects (Figs 9.8 to 9.11) must be substantiated by clinical examination of the retina and optic nerve head. The first visual field test in an inexperienced patient should be taken with caution. After first test the patient becomes more proficient; the resulting improvement in the visual field is known as learning curve. It is, therefore, desirable to test two or more visual fields before proper interpretation. To be clinically significant, the visual field should be reproducible.

While assessing single field printout, the presence of miotic pupil and media opacities should be taken into consideration because they can cause generalized depression of visual field. The interpretation should also include allowance for artifacts such as position of the patient, correcting lens (Fig. 9.12), drooping of the lid and prominent brow. It is not rare to find that visual field changes in neurological disorders (Fig. 9.13) may mimic the glaucomatous field defects.

The visual field examination is a useful tool to study the course of an eye disease as well as to monitor the therapy. Periodic visual field testing is usually recommended for all glaucoma patients especially with a view to evaluate the desired target intraocular pressure. In spite of good control of the pressure, the patient’s visual fields may show deterioration on follow-up (Fig. 9.14) while in some patients the fields remain stationary (Fig. 9.15). Assessment of progression is difficult because of the long-term fluctuations. One needs to repeat the field test when in doubt. In clinical practice the recent fields are compared with the earlier baseline fields to judge the progression.

Conclusion

In conclusion automated perimetry is an extremely useful tool which has also become the standard technique for evaluating the visual field in patients with glaucoma or glaucoma suspects. Interpretation of the results is difficult and requires experience in addition to a detailed understanding of the underlying principles of automatic static perimetry and the applied statistical analysis.

A word of caution is necessary. Automated perimetry should never be used in isolation. Treatment of patients requires combining the results of automated perimetry with an

Fig. 9.8: Humphrey single field 24-2 SITA standard test of the left eye of a 53 year old patient. Reliability factors

have been expressed as a percentage. The visual field is markedly depressed in the inferior hemisphere on the gray scale and total deviation plot. Anderson’s criteria are fulfilled. The height of the hill island of vision represented by the mean deviation is significantly reduced. Clinical correlation with the amount of optic disk cupping is necessary to determine the cause of such a defect

Fig. 9.9: Humphrey single field 30-2 full threshold test of the left eye of a 64 year old patient. High false positives

are bracketed. The gray scale and the total deviation plot show a marked depression of the visual field. However, only a cluster of points on the pattern deviation plot (p<2%) in the central 10 degrees are seen. No probability symbols are seen alongside the CPSD and the Glaucoma Hemifield test is showing a borderline/generalized reduction in sensitivity

Fig. 9.10: Octopus 1-2-3 seven in one single field printout of the left eye of a 61 year old male patient showing an early inferonasal step. There are a number of adjacent points in the inferonasal quadrant on the corrected probability plot, depressed to 5%, one of which is depressed to less than 1%. The left part of Bebie’s curve shows a localized depression. The corrected loss variance is 8.4. This field needs to be correlated clinically

Fig. 9.11: Octopus 1-2-3 seven in one single field printout of the left eye of a 61 years old male patient to assess

fixation characteristics. Here the catch trials are suggestive of poor reliability. The gray scale and comparisons are suggestive of depression of the inferior part of the 10 degrees being tested. Within the central 4 degrees of this program, each point is 0.7 degrees apart. This helps to assess fixation characteristics better. One of the four fixation points is depressed p < 2%. The Bebie’s curve is initially suggestive of normal points corresponding to the superior part of the field. A sudden drop in Bebie’s curve is due to the cluster of depressed points in the inferior part of the field. The CLV is also significant. This field is suggestive of extensive damage in the inferior hemisphere which is threatening fixation and needs to be correlated clinically

Fig. 9.12: Humphrey single field 24-2 full threshold test of the left eye of a 52 years old patient. A ring scotoma

on the gray scale and the pattern deviation plot is evident. Anderson’s criteria are also fulfilled. Such visual field loss could be due to glaucoma or retinitis pigmentosa. However, the fundus findings were normal and on repeating the field test (with proper positioning of the lens) the changes in the pattern deviation plot disappeared (Lens rim artifact)

Fig. 9.13: Humphrey single field 30-2 full threshold test of the right eye of a 59 years old patient. The gray scale and the total deviation plot show a depression of the visual field. Here the gray scale shows a marked temporal depression as is evidenced on the pattern deviation plot. Such defects which respect the vertical meridian are neurological in origin. In this patient the other eye also showed a temporal hemianopia

examination of the complete eye especially the retina, optic nerve and visual pathway.

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