Pulsar Perimetry in the Diagnosis of Early Glaucoma

In a recently published article, Zeppieri and associates affirm that Pulsar perimetry shows lower sensitivity than other procedures for the diagnosis of glaucoma in cases where morphologic defect precedes functional defect (glaucomatous optic neuropathy; GON). However, the optic nerve head size of patients in the GON group is clearly larger (2.13 ± 0.46 mm 2 ) than that of normal reference subjects (1.81 ± 0.51 mm 2 ), which raises the suspicion that many patients in the GON group were not in fact glaucomatous.

This suspicion is heightened by the fact that 43.7% of the group with ocular hypertension (OHT) presented an abnormal disc area, as shown in Figures 3 and 4. The influence of disc area in glaucoma is minimal or irrelevant, and larger disc area is known to be significantly associated with decreased specificity of Heidelberg Retina Tomograph (HRT) results.

It is therefore evident that an abnormal appearance of the optic nerve head due to its size influenced the inclusion of false cases in the OHT group. It is highly likely that the same occurred with the inclusion of patients in the GON group, who presented much greater optic nerve head size and, therefore, more pronounced cupping.

In addition, the “best cut-off” point selected by the authors in their receiver operating characteristic (ROC) curve analysis is, apparently, the point of greatest equilibrium between sensitivity and specificity. The choice of this cut-off point is important since some of the authors’ main conclusions are based on it. Unfortunately, it leads to some clearly biased and erroneous results. For example, in Tables 3 and 4, the cut-off point for the disc area yields a sensitivity of nearly 60% for the diagnosis of glaucoma, which is clearly untenable.

It is widely accepted that the early diagnosis of glaucoma should be established using criteria of high specificity. If not, a large number of normal subjects would be erroneously considered as cases of suspected glaucoma and treated unnecessarily. This error is clearly more serious than delaying the diagnosis of suspected glaucoma, which should be periodically evaluated. A regularly monitored patient can easily be correctly treated as from an early phase of the disease.

Tables 3 and 4 indicate that, for a specificity of 95%, Pulsar proved more sensitive than frequency doubling technology (FDT), even in the GON group, and much more sensitive than GDx, a procedure less dependent on disc area that theoretically should show early alterations in patients with GON. At this level of specificity, the results obtained with HRT, although probably subject to diagnostic bias, are not significantly better than those obtained with Pulsar.

Given these considerations, the authors’ affirmation of GON patients’ being an exception regarding the advantages of Pulsar perimetry for the early diagnosis of glaucoma is probably misguided.

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Jan 16, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Pulsar Perimetry in the Diagnosis of Early Glaucoma
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