Outer Retinal Tubulation Update
Rachel T. Samouha, OD
Outer retinal tubulation (ORT) is a structure identified on spectral-domain optical coherence tomography (SD-OCT) in patients with degenerative retinal disorders. It is characterized by round or ovoid hyporeflective tubular spaces surrounded by hyperreflective borders found in the retinal outer nuclear layer on the B-scan of SD-OCT.1 ORTs are often misinterpreted as cystic areas of intraretinal or subretinal fluid, thus leading to unnecessary treatment.
The pathogenesis of outer retinal tubulation formation is not completely understood but is known to involve injury to the photoreceptors and retinal pigment epithelium (RPE). Reorganization of remaining or degenerating photoreceptors and/or external limiting membrane (ELM) occur as a response to injury, where cells fold inward in an attempt to connect viable tissue.2,3 Schaal et al studied the histological foundation of ORTs and classified the structures into four phases based on the contents found within the tubule walls. The phases were categorized as nascent, mature, degenerate, and end stage, where the makeup of the lumenal wall contained outer segments (OS) and inner segments (IS) of photoreceptors, IS only, degenerating or no IS, or Muller cells forming ELM, respectively. ORTs have also been documented to exist in either a closed or open configuration.2 The lumen of outer retinal tubulations may consist of hyperreflective material on SD-OCT, corresponding to RPE cells, lipofuscin, or mitochondria.2
ORTs were originally observed in advanced stages of age-related macular degeneration (AMD) in patients with presentations of severe photoreceptor loss, choroidal neovascularization (CNV), and geographic atrophy. However, various retinal degenerations, dystrophies, and disorders have been associated with the presence of these tubular structures including degenerative myopia, gyrate atrophy, Bietti crystalline dystrophy, Best disease, retinitis pigmentosa, Stargardt disease, acute zonal occult outer retinopathy, retinal detachment, and numerous other conditions.4,5,6
In eyes with outer retinal tubulations that concurrently received treatment with intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections, the majority of the tubular structures have been documented to remain stable over time; however, some ORTs have been recorded to transiently collapse with anti-VEGF treatment.1,7 It has been hypothesized by Zweifel et al that this phenomenon may occur secondary to incidental fluid leakage from an underlying CNV into the tubule due to occasional communication between ORTs and the subretinal space. Espina et al disagree with this theory since this evolvement manifested in eyes with closed ORT configurations (described by Schaal et al); rather, they believe that ORTs may periodically contain vascular-related structures that temporarily respond to anti-VEGF treatment. Spontaneous collapse of ORTs may also occur, independent of treatment with anti-VEGF.7
It is of clinical significance to be able to differentiate outer retinal tubulations from areas of intraretinal or subretinal fluid. ORTs are commonly misconceived as cystoid macular edema (CME). Fundamental markers that may help to avoid formation of this error include recognition of the hyperreflective border enveloping the outer retinal tubulations as well as the location of ORTs within the outer nuclear layer; CME does not comprise of a hyperreflective boundary and is usually localized at or above the outer plexiform layer.
In conclusion, outer retinal tubulations are structural findings characterized on SD-OCT that occur in the setting of advanced stages of degenerative retinal disease affecting the outer retina and RPE. ORTs must be distinguished from other masqueraders as they do not require treatment with anti-VEGF unless fluid is present.
- Zweifel, S. A., Engelbert, M., Laud, K., Margolis, R., Spaide, R., & Freund, B. (2009). Outer Retinal Tubulation A Novel Optical Coherence Tomography Finding. Archives of Ophthalmology, 127(12), 1596-1602.
- Schaal, K. B., Freund, K. B., Litts, K. M., Zhang, Y., Messinger, J. D., & Curcio, C. A. (2015). Outer Retinal Tubulation In Advanced Age-Related Macular Degeneration: Optical Coherence Tomographic Findings Correspond to Histology. Retina, 35(7), 1339-1350.
- Preti, R. C., Govetto, A., Filho, R. G., Zacharias, L. C., Pimentel, S. G., Takahashi, W. Y., Monteiro M. L. R., Hubschman, J. P., Sarraf, D. (2018). Optical Coherence Tomography Analysis Of Outer Retinal Tubulations, Sequential Evolution and Pathophysiological Insights. Retina, 38(8), 1518-1525.
- Braimah, I. Z., Dumpala, S., & Chhablani, J. (2017). Outer Retinal Tubulation In Retinal Dystrophies. Retina, 37(3), 578-584.
- Rousso, L. A., Rodman, J. A., Sutton, B., & Shechtman, D. L. (2017). Outer Retinal Tubulation: A Case Series. Optometry and Vision Science, 94(3), 423-431.
- Seidman, C., Kiss, S., & Orlin, A. (2019). Outer Retinal Tubulations In Chronic Rhegmatogenous Retinal Detachment. Retinal Cases & Brief Reports, 13(1), 47-49.
- Espina, M., Arcinue, C. A., Ma, F., Camacho, N., Barteselli, G., Mendoza, N., Ferrara, N., Freeman, W. R. (2015). Outer retinal tubulations response to anti-VEGF treatment. British Journal of Ophthalmology, 100(6), 819-823. doi:10.1136/bjophthalmol-2015-307141
About the Author:
Dr. Rachel T. Samouha is an optometrist who graduated from the State University of New York College of Optometry. She is currently an Assistant Clinical Instructor at the State University of New York College of Optometry where she is completing a residency in Ocular Disease.