Outer Retinal Tubulation
Dr. Rashmi Nagar, Dr. Sarang Lambat, Dr. Prabhat Nangia, Dr. Vinay Nangia
Suraj Eye Institute, 559, New Colony, Sadar, Nagpur- 440001.
Case Description
A male, 50 years of age came to our institute with complaints of blurring of vision for distance and near for the past 2 years. His best corrected visual acuity was 6/12, N10 in both eyes. Slit lamp examination showed pseudophakia in right eye and early cataract in left eye. Intra-ocular pressure was 20 mmHg in both eyes. He was a known case of Hypertension, Diabetes mellitus and Ischemic heart disease. On dilated fundus examination and colour fundus photography multiple drusen and patches of geographic atrophy were seen in both eyes. Spectral domain optical coherence tomography confirmed the clinical findings.
Figure 1(b) – Colour fundus photograph of LE shows multiple whitish-yellow spots in the macula suggestive of drusen (green arrows) and patches of geographic atrophy (red arrows).
Figure 3b – Infrared photograph of the right eye showing the locations of different ORTs (black circle – ORT No.1, cyan circle – ORT No.2, yellow circle – ORT No.3, blue circle – ORT No.4, pink circle – ORT No.5 and red circle – ORT No.6).
Figure 3c – OCT line scan passing through the ORT No.1 at section 32/61 of the posterior pole scan.
Figure 4b – OCT line scan passing through ORT No.1 at section 32/61 of the posterior pole scan.
Figure 4c – OCT line scan passing through ORT No.1 at section 33/61 of the posterior pole scan.
Figure 4d – OCT line scan passing through ORT No.1 at section 34/61 of the posterior pole scan.
Note: The line scans in the posterior pole scan are counted from below upwards.
Areas of loss of external limiting membrane and the photoreceptors (blue arrows) with distortion of the outer retinal layers are also seen.
Figure 6d – Scan at section 40/61 shows a small hypo-reflective lesion is seen surrounded by a hyperfluorescent ring suggestive of an ORT, a spot of hyper-reflectivity is also seen in the center – ORT No.4 (blue arrow).
Figure 6f – Scan at section 47/61 shows a small hypo-reflective lesion is seen surrounded by an incomplete hyperfluorescent ring suggestive of an ORT in formation – ORT No.5 (pink arrow).
Figure 6h – Scan at section 21/61 shows a small hypo-reflective lesion is seen surrounded by a hyperfluorescent ring suggestive of an ORT, a spot of hyper-reflectivity is also seen in the center – ORT No.6 (red arrow).
Figure 7b – Inner horizontal and vertical dimensions of the ORT No. 1 were measured to be 109 microns and 56 microns respectively.
Discussion
The process of ORT formation likely begins with outward folding of photoreceptors at the junction of intact and disrupted IS/OS, and eventual formation of a long ovoid tubular complex which, over time, may reassemble into smaller round rosettes. A similar mechanism due to degeneration in Geographic Atrophy may play a role in development of ORTs in such patients.
In AMD patients who have undergone anti-VEGF therapy, only minimal change has been noted in the size and shape of the tubular structures after treatment. The eyes which had ORT related to AMD, poor visual acuity and poor response to therapy has been noted. Eyes with ORT are also seen to show slower enlargement of geographic atrophy. ORTs are seen to remain stable over time and do not require any treatment. It is important to diagnose ORT, since they can be confused with intra-retinal or sub-retinal fluid since they do not require any treatment.
In our patient, we found the presence of 6 ORTs in the RE. The patient had Geographic atrophy and associated drusen. There was no presence of wet AMD. The number of ORTs found in one eye was rather high. Note the distribution of the ORTs on the colour photos and on the infrared image (Figure 3a and 3b). The ORT No. 1. was the biggest and the most visible (Fig.3a – black circle and Fig.3c – yellow arrow). The predominant distribution was superior to the fovea. The left eye did not show any obvious ORTs. ORTs have been visualized on the OCT to form a circle with a hyperreflective border and a hypo reflective center. The evolution of the rosette from the origins described above, would indicate, that there would be several stages before the photoreceptors get organized as a typical ORT. Therefore, it is possible that evolving ORTs or aborted ORTs may not be recognized and may be atypical but may indicate a part of same spectrum of pathology. However, the behavior of photoreceptors as a response to retinal degeneration and atrophy shows varying responses. i.e., that not all disorganization of the photoreceptors will result in typical ORT formations. What may be important is to consider the disorganization of the photoreceptors in such situations, even if one does not find evidence of an ORT as an indicator of the severity of the retinal disease.
In our patient, the biggest ORT was ORT No.1. It extended from line scan 31/61 to 34/61. Using the posterior pole scanning, the sections showed a variation in the height and width of the ORT along different line scans. We attempted to draw the ORT and the shape was that of a spindle (Fig.8) arranged so that the longer length of the spindle was along the vertical axis i.e.from superior to inferior on the retina and the shorter diameter of the spindle was along the horizontal axis on the retina. The lowest section of ORT No.1 section 31/61 shows a hyper reflective inferior tip of the spindle (Fig 4a yellow arrow). Fig 4b, Section 32/61 shows widest dimension of the tubule. Fig 4c, Section 33/61 shows an incomplete tubule with two prominent hyper reflective spots and Fig 4d, Section 34/61 also shows a tubule formation. The ORT No.1 was not visible beyond these sections superior and inferiorly. Calculating the space between the posterior pole scans we calculated the length of the spindle of the tubule to be 484 microns.
The asymmetry of the frequency of ORT presence in the RE versus the LE is difficult to explain. There may also be ORTs in evolution, but because they may not have the particular shape that has been described, we may not have considered their presence or recognized them as such. One may like to think, whether the ORT is a random development or is a biomarker for such patients regarding their further visual and pathologic progress. Perhaps a further detailed study including more subjects with adequate follow up may help. At least in this subject, there was a significant degree of geographic atrophy in both eyes. But clinically and on autofluorescence there were larger areas of atrophy in the RE compared to the LE. It may be important to note that ORTs may look like an area of fluid accumulation, which may lead to inadvertent treatment with anti-VEGF injections. They can be differentiated from the latter by the presence of a reasonably well-defined and hyper-reflective rim.
ReadWise:
1. Goldberg NR, Greenberg JP, Laud K, Tsang S, Freund KB. Outer retinal tubulation in degenerative retinal disorders. Retina (Philadelphia, Pa.). 2013 Oct;33(9):1871. doi:10.1097/IAE.0b013e318296b12f
2. Zweifel SA, Engelbert M, Laud K, Margolis R, Spaide RF, Freund KB. Outer retinal tubulation: a novel optical coherence tomography finding. Archives of ophthalmology. 2009 Dec 14;127(12):1596-602. doi:10.1001/archophthalmol.2009.326
3. Litts KM, Messinger JD, Dellatorre K, Yannuzzi LA, Freund KB, Curcio CA. Clinicopathological Correlation of Outer Retinal Tubulation in Age-Related Macular Degeneration. JAMA Ophthalmol. 2015;133(5):609–612. doi:10.1001/jamaophthalmol.2015.126
4. Lee JY, Folgar FA, Maguire MG, Ying GS, Toth CA, Martin DF, Jaffe GJ, CATT Research Group. Outer retinal tubulation in the comparison of age-related macular degeneration treatments trials (CATT). Ophthalmology. 2014 Dec 1;121(12):2423-31. https://doi.org/10.1016/j.ophtha.2014.06.013
Dr Vinay Nangia
MS, FRCS, FRCOphth
Director
Suraj Eye Institute
Email – education@surajeye.org