I have read with great interest the recent articles regarding the glaucoma diagnostic ability of macular ganglion cell-inner plexiform layer (GCIPL) thickness as determined by optical coherence tomography (OCT) published in
Investigative Ophthalmology & Visual Science.
1–3 The studies reported that the macular GCIPL thickness showed good glaucoma diagnostic ability. According to my clinical observations, GCIPL abnormality was found in various ocular conditions, including myopia, macular degeneration, epiretinal membrane (ERM), and compressive optic neuropathy due to pituitary gland tumor, as well as glaucoma. Given that these conditions can cause visual field defects, and can present simultaneously with glaucoma, identifying different patterns of macular GCIPL abnormalities in various ocular conditions may enhance glaucoma diagnostic ability by using GCIPL thickness measurement.
In early stages of glaucoma, macular GCIPL thinning is predominantly located in the inferotemporal or superotemporal area around the horizontal raphe.
4 Thinning of GCIPL associated with myopia is mainly located in the inferior or superior area, and presents as a horizontal crescent-shaped abnormal area.
4 It should be noted that in very high myopia, the entire macular area appears as an abnormal GCIPL area, making it difficult to interpret. In conditions with early macular degeneration, GCIPL thinning is observed around the fovea with a ring-shaped abnormal area (
Fig., first column). The epiretinal membrane can cause thinning or thickening of macular GCIPL with irregular patterns (
Fig., second and third columns). Thickening of GCIPL associated with ERM can lead to misidentification of GCIPL thinning associated with glaucoma (
Fig., third column). Further, severe ERM can cause errors in segmentation algorithm of GCIPL thickness measurement. When pituitary gland tumor compresses the optic chiasm, subsequent macular GCIPL thinning can be presented as a vertical half-moon–shaped abnormal area in the nasal area of the macula, which can be distinguished from the glaucomatous changes owing to its specific feature (
Fig., fourth column). In addition to these conditions, other retinal disorders and optic neuropathies, such as diabetic retinopathy, retinal vein occlusion, retinitis pigmentosa, ischemic optic neuropathy, and optic neuritis also cause GCIPL thinning or thickening. However, these conditions do not show specific patterns. Therefore, it is difficult to characterize the pattern of GCIPL abnormality in these conditions.
Taken together, any macular abnormalities can affect GCIPL thickness assessment by OCT. Thus, when investigating macular GCIPL thickness for the detection of glaucomatous changes, it should be interpreted with caution.