Winter 2011 Insert Winter 2011 Insert

Case Studies

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Case No.1 Early Perimetric Glaucoma
Figure 1A shows the Humphrey Field Analyzer (HFA; Carl Zeiss Meditec, Inc., Dublin, CA) visual field single field analysis report for a 34-year-old man with early glaucoma and an abnormal Glaucoma Hemifield Test (GHT) on Swedish Interactive Threshold Algorithm (SITA) Standard.

The GHT is an automated, empirically derived algorithm that detects up-down asymmetry and symmetrically depressed visual field abnormalities.1 By comparing five corresponding sectors from the superior and inferior hemifields, the GHT serves as a sensitive indicator of focal visual field loss. Analysis of this patient’s glaucomatous visual field (Figure 1A) shows only two significantly (P < .5%) depressed points on the total and pattern deviation plots. Although only a small region of the field is depressed, these two points are deeply depressed at 12 dB and 9 dB below the ageadjusted normal, as seen on the total deviation plot. The fixation losses, false positive and false negative errors are all within acceptable limits, and the gaze tracker demonstrates steady fixation. The prior SITA Standard test from several months earlier was completely normal, and fluctuation between normal and abnormal results may occur in early perimetric glaucoma.2 Note that the Visual Field Index (VFI) is still high at 96%, demonstrating that very little field loss is required in order for the GHT to become abnormal. The mean deviation is still in the positive range at +0.13 dB, indicative of the overall preserved hill of vision. The focal superior defect has distorted the shape of the hill of vision, however, causing the pattern standard deviation to be 2.92 dB, a value found in less than 2% of the normal population. The patient was informed that a small region of the superior visual field demonstrates characteristic visual field loss from glaucoma.

Figure 1B presents the bilateral Cirrus HD-OCT (Carl Zeiss Meditec, Inc.) optic nerve head (ONH) and retinal nerve fiber layer (RNFL) analysis. There is a good structure-function relationship between the inferior RNFL defect and the superior scotoma. Interestingly, the superior RNFL defect is not accompanied by an inferior perimetric deficit, indicating that a region of preperimetric neuropathy has been detected by the sensitive optical coherence tomography RNFL deviation map.

Case No.2 Moderate Glaucomatous Field Loss
Figure 2A shows the results of SITA Standard testing for a 26-year-old man with juvenile primary open-angle glaucoma.

The fixation losses and the false positive and false negative errors are all within acceptable limits. The gaze tracker demonstrates steady fixation with a brief period of unstable gaze about three-quarters of the way through the test. The GHT is outside normal limits. The total deviation plot reveals a paracentral superior arcuate scotoma with a more peripheral inferior arcuate scotoma, each respecting the horizontal meridian. Although a dense paracentral focal defect is present, the central visual acuity is unaffected, as reflected by the patient’s 20/15 visual acuity and by the normal foveal sensitivity value of 41 dB.

The presence of superior and inferior hemifield defects in addition to the paracentral vision loss would place this visual loss in the moderate category, despite the seemingly high VFI value of 90%. The mean deviation is abnormal but still modest at -3.14 dB, but it is smaller than the pattern standard deviation at 5.99 dB, likely because the dense superior paracentral scotoma has distorted the shape of the hill of vision. The patient was informed that there is damage to both the superior and inferior visual field and that the superior damage is approaching his central vision and must be carefully monitored.

A strong structure-function relationship is seen on comparison with the Cirrus HD-OCT (Figure 2B).

Case No.3 Advanced Glaucoma
A 64-year-old woman presented with blurred vision in her left eye and was found to have both cataract and glaucoma in this eye. Her visual acuity was 20/50 and could not be improved with refraction. The reliable HFA 24-2 demonstrated both superior and inferior arcuate scotomata that involved her central field, with the GHT outside normal limits.

Of greatest concern was the total deviation plot demonstrating four depressed points surrounding fixation along with the foveal sensitivity value of 22 dB (a value found in less than 0.5% of the normal population). The mean deviation was -7.78 dB, and the pattern standard deviation was 10.57 dB. The VFI is 65% in this case, and it is notable that, in this particular patient, the majority of the visual loss has occurred in the central visual field. To further investigate the central field, a central 10-2 threshold test was performed, which revealed a small central/temporal island of remaining vision.

The SITA Standard strategy and stimulus size III were chosen in order to take advantage of the normative database that allows us to review the total and pattern deviation plots. Although the total deviation plot might seem to leave open the possibility of preserved fixation, the reduced foveal sensitivity on both examinations strongly suggests that the patient’s visual acuity was reduced from glaucoma. In this clinician’s experience, it is unlikely that glaucoma patients with reduced foveal sensitivity will regain normal visual acuity after cataract extraction. Although this does not always preclude cataract extraction, this finding can provide valuable insight and may help manage expected outcomes in advanced glaucoma. The patient was informed that significant visual field loss, most likely from glaucoma, was affecting her central vision.

Nathan M. Radcliffe, MD, is the director of the glaucoma service and an assistant professor of ophthalmology at Weill Cornell Medical College, New York-Presbyterian Hospital, New York. He has served on the speaker’s bureau for Carl Zeiss Meditec, Inc. Dr. Radcliffe may be reached at (646) 962-2020;

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