Relatively less affected VF structures were the arcuate two region in normal-tension eyes and central regions of PACG and high-tension eyes. Photo: Joseph Sowka, OD. Click image to enlarge.

Research conducted in China recently assessed patterns of field loss that may appear distinct by glaucoma classification. A total of 48 primary angle-closure glaucoma (PACG) eyes were enrolled with controls of primary open-angle glaucoma and normal-tension glaucoma matched for age, sex and mean deviation of visual field (VF) defect.

VF was assessed using the 24-2 test, and defects were classified into six patterns using the Ocular Hypertension Treatment Study’s classification system. Variables included were three disease stages (early, moderate and advanced) and five separate hemifield regions guided by the Glaucoma Hemifield Test.

The study researchers found the PACG group to have a greater rate of partial arcuate VF defects than the other two groups. Specifically, mean total deviation was worst in this group in the nasal hemifield test region in the inferior hemifield, followed by the arcuate one, arcuate two, paracentral and central regions. Indicative of irregular vision, the central region’s mean total deviation was much better than all other regions. The superior hemifield in the PACG group yielded a similar trend that was not observed in the VF hemifields of the high-tension and normal-tension groups.

A partial arcuate was the most common type of field defect in PACG eyes, while altitudinal and partial arcuate defects were most common in high-tension open-angle eyes and arcuate defects were most common in normal-tension eyes. Based on these findings, the authors noted that “the differences in the pathogenic mechanisms of glaucomatous optic neuropathy between PACG and primary open-angle glaucoma may play a role in this discrepancy in VF defects.”

This potential difference in pathogenic mechanisms is also highlighted by their observation that PACG and high-tension eyes typically had more diffused VF loss than normal-tension eyes. However, it should be noted that among the regions within almost every hemifield in the three subtypes, the nasal region was more depressed than others, indicating that the most significant VF damage was done to this area.

According to the authors, VF defect location is related to structural changes of the optic nerve head caused by glaucoma. The VF defects seen in the superior and inferior nasal regions of the Glaucoma Hemifield Test indicate inferotemporal and superotemporal glaucomatous damage to the optic nerve head, respectively, according to the Garway-Heath structure-function map. Along with this, glaucomatous damage occurs preferentially in the inferotemporal and superotemporal optic nerve head sectors.

The researchers highlighted that since normal-tension and high-tension glaucoma eyes had higher pattern standard deviation than seen with PACG eyes, this “suggests that the VF defect in POAG eyes is more localized than in PACG eyes at the same level of overall VF damage.”

Normal-tension eyes had higher pattern standard deviation than those with high-tension for a given mean total deviation, meaning normal-tension eyes display localized VF defects more than their high-tension counterparts. To this, the researchers concluded that “primary glaucoma with lower IOP tends to produce more localized field defects than cases with higher pressure.”