• Written By: Jeffrey Freedman, MD, BCh, PhD, FRCSE, FCS

    This study published in the September issue of Ophthalmology compared the clinical characteristics of glaucoma patients who present with either an initial isolated parafoveal scotoma (IPFS) or an initial nasal step (INS) in which the central or paracentral visual field is unaffected. The authors found that the IPFS group of patients had a significantly lower maximum untreated IOP and a higher frequency of disc hemorrhage (DH) detection than the INS group and a higher prevalence of systemic hypotension, migraine, Raynaud's phenomenon and sleep apnea. The results suggest that IPFS patients, glaucoma suspects or patients with a low maximum untreated IOP or systemic vascular factors should be more carefully observed with a shorter interval between visits and intermittent 10-2 visual fields or more aggressively treated.

    The authors retrospectively examined the records of 69 patients with glaucoma with an isolated IPFS and 53 patients with an isolated INS seen at one glaucoma referral practice during a seven-month period. In patients with an IPFS compared with those with an INS, maximum untreated IOP was 21.6 ± 4.5 vs. 28.3 ± 9.6 mmHg (P < 0.001) and frequency of DH detection was 44 percent vs. 17 percent (P= 0.001). Hypotension, migraine, Raynaud's phenomenon and sleep apnea occurred in 16, 23, 24 and 9 percent of IPFS patients, respectively, compared with 0, 4, 9 and 0 percent of INS patients, respectively (P = 0.001, 0.002, 0.025 and 0.030, respectively). Mean deviation was similar between the two groups (P = 0.346), but pattern standard deviation was significantly greater in the IPFS group than the INS group (P = 0.043).

    The authors say the results suggest that the development of an IPFS may be more associated with IOP-independent risk factors compared with an INS and that pathogenetic mechanisms in addition to or other than IOP may play an important role. They postulate that in the early stage of glaucoma, IOP-independent factors associated with decreased or unstable ocular perfusion may preferentially damage the neuroretinal rim or retinal nerve fiber layer closer to the papillomacular bundle in the inferior half of the optic nerve head or retina, compared with elevated IOP. They conclude that the pattern of the visual field loss may be useful for identifying different glaucomatous pathogenetic mechanisms and underscores the limitations of using terminology, such as normal-pressure glaucoma or high-pressure glaucoma, to identify glaucoma populations with different risk characteristics.