Typically, spectral-domain OCT is a clinically useful tool for imaging the retinal nerve fiber layer (RNFL).1 In fact, seven years ago, it was called “the most advanced commercially available application of OCT technology.”1 But a new study is showing that doctors should take a few contingencies into account—and reminder that imaging technologies exist to aid a clinical examination, not replace it.2
According to the Korean Journal of Ophthalmology, “when epiretinal membranes (ERM) occur in glaucoma patients, clinicians should be aware that RNFL thickness measurements obtained with a SD-OCT may underestimate the status of glaucomatous optic neuropathy.”2
In the words of Joseph Sowka, OD, “OCT is not a Silicon Valley Rumplestilskin: You cannot put in straw and get out gold,” he said, in reference to the study at the 2019 American Academy of Optometry conference in Orlando, Florida. “The use and overemphasis of imaging technology to the exclusion of other clinical findings and assessment of risk factors will put you and your patients in peril.”3
The researchers looked at 28 eyes from 28 patients and found the average RNFL thickness increased by a mean of 4.0µm±7.4µm after ERM onset. They noted an increase in the superior, nasal and temporal quadrant RNFL thicknesses. The change in the temporal RNFL thickness was significant. However, the inferior thickness decreased. In the visual field examination, the mean deviation decreased significantly.2
The study suggests that clinicians need to take into account the relationship between ERM and RNFL thickness before using it as a metric of glaucoma progression. Specifically, it outlines three implications of their findings:
- Diagnosing glaucoma in patients with ERM, in which the boundary of the RNFL defect is not clearly demarcated and the glaucomatous visual field defect is not apparent, can be delayed because of peripapillary RNFL thickening caused by ERM, which can obscure diffuse or localized thinning of the RNFL.
- Detection of the glaucomatous progression can be delayed if ERM newly occurs in patients with glaucoma, in which visual field progression is not considerable.
- Patients who undergo vitrectomy and ERM removal may be misdiagnosed with glaucoma if RNFL thinning is detected.
The significant increase in RNFL thickness following the onset of ERM in those with glaucoma means SD-OCT may underestimate disease progression for these patients. This emphasizes the notion that the imaging technology should not be the deciding factor in treatment decisions.
1. Tariq Y, Li H, Burlutsky G, Mitchell P. Retinal nerve fiber layer and optic disc measurements by spectral domain OCT: normative values and associations in young adults. Eye (Lond). 2012;26(12):1563-70.
2. Kim J, Kim K, Kim W, Kim C. Influence of epiretinal membranes on the retinal nerve fiber layer thickness measured by spectral domain optical coherence tomography in glaucoma. Korean J Ophthalmol. 2019;33(5):422-9.
3. Sowka J. Mistakes to avoid in glaucoma. Academy 2019 Orlando.