Comparison of Local Structure–Function Relationships and Dynamic Range in Glaucoma

Miraftabi et al.¹ recently tested the hypothesis that the macular ganglion cell layer (GCL) thickness demonstrates a stronger structure–function relationship, may extend the useful range of macular measurements compared with combined macular inner layer or full thickness, and may be a better outcome measure for detection of glaucoma progression. They found that measuring the GCL did not result in a stronger structure–function relationship with central visual field sensitivity measurements compared with ganglion cell–inner plexiform layer (GCIPL) or ganglion cell complex (GCC) thickness. However, there are several concerns. (1) This study included 98 glaucomatous eyes and 8 normal eyes. The difference of sample size between the glaucoma and the normal control group is great. The authors should provide more details about how the sample size was calculated. (2) The study was a cross-sectional observation study, which could not provide the exact cause-and-effect relationship between structural measures and visual field defect (structure–function relationship). In the recent study from Öhnell et al.,² in eyes with manifest glaucoma, progression in the visual field was detected first more than four times as often as progression in the optic disc. Therefore it will be important to conduct a prospective and longitudinal trial to explore which inner macular parameters are more sensitive for detecting glaucoma and the progression of glaucoma.