Spark ImageWise 35

Atypical Ganglion Cell Loss in Glaucoma

Dr. Rashmi Nagar, Dr. Prabhat Nangia, Dr. Sarang Lambat, Dr. Vinay Nangia
Suraj Eye Institute, 559 New Colony, Nagpur.

Case Description
A male 53 years of age presented to us with complaints of gradual blurring of vision in both eyes over a period of 1 year. He was a known case of Diabetes mellitus type II, hypertension and primary open angle glaucoma.  Best corrected visual acuity was 6/6, N6 in the right eye (RE) with an addition of +2.25 DS for near vision and 6/9, N6 in the left eye (LE) with an addition of +2.25 DS for near vision. Slit lamp examination showed a normal anterior segment. Intra-ocular pressure was 26mmHg in RE and 30mmHg in LE. He was on four anti-glaucoma medications – Brinzolamide, Brimonidine, Ripasudil and Travoprost. He had no history of cigarette smoking or tobacco chewing.

Figure 1 – Colour fundus photograph of RE shows vertical CDR of 0.7:1. Gunn’s dots are also seen along the superior arcade (yellow arrow).
Figure 2 – Colour fundus photograph of LE shows VCDR 0.8:1 with inferior rim thinning (red arrow) and wedge defect inferior to disc (yellow dashed lines) suggestive of retinal nerve fiber layer defect. Gunn’s dots are seen along the superior arcade (yellow arrows).
Figure 3- Spectral Domain OCT (SD-OCT) circumpapillary RNFL (pRNFL) scan of RE shows mild global RNFL thinning on the graph (D – red arrow).
Figure 4- SD-OCT pRNFL scan of left eye (OS) shows significant RNFL loss infero-temporally and supero- temporally (B – yellow arrows) and severe thinning on thickness map corresponding to sudden drop of RNFL thickness seen as a notch (C – red arrows) on the graph.
Figure 5– SD-OCT posterior pole deviation map of right eye shows unusual ganglion cell layer (GCL) loss (B – blue arrows) supero-nasal, nasal and infero-nasal to the fovea.
Figure 6– SD-OCT posterior pole deviation map of left eye shows extensive GCL loss (B – blue arrows) temporo-superior and temporo-inferior to the fovea.

Discussion

Our patient is a classical case of POAG.  There is presence of significant RNFL loss (Fig. 2 yellow dashed lines and Fig. 4 b, yellow arrows) specially in the LE. The RNFL appears to be normal in the RE (Fig. 3 b,c). However, Fig 3 d shows some global thinning. Do note the presence of Gunn’s dots in both eyes (Fig. 1 and 2. yellow arrows). Gunn’s dots form linear refractile appearance lined along the RNFL pathways.  In the LE it is interesting to note that they are present even after significant RNFL loss. By enhancing contrast, they tend to clinically help in identifying areas of RNFL loss.

In the LE the ganglion cell map shows a classical loss of GCL that matches with the pattern that one expects in a patient with glaucoma. There is also the expected correlation of the GCL loss with the RNFL loss and the area of neuroretinal rim loss. In the RE however, we have already noted that the RNFL is reasonably normal, other than the presence of some global loss. The heat map of the GCL of the RE, instead of showing the expected classical early loss pattern reflected in the temporal and infero temporal area, shows a loss affecting the nasal area (Fig. 5 A blue arrows). Likewise the deviation map of GCL in RE shows naso-superior, nasal and naso-inferior loss of the GCL. Again, this is unlike what we might expect in a patient of glaucoma. We looked at the segmentation of the retinal layers and did not find any error. A GCL loss of this type may occur due to optic disc pathology not of glaucomatous origin.  However, the patient did not give any history or show any clinical signs that may explain this pattern of loss.  We were unable to offer an explanation in this patient for this finding. This tells us that even in a patient with classical POAG, there may be the possibility of a second etiology for optic disc damage, which may add to the apparent glaucomatous changes.

In some patients we may not be able to solely depend on clinical findings since they may not give complete and accurate information about the extent of damage. Therefore, further detailed investigations may help in elucidating the diagnosis and planning of management in optic disc pathology.

ReadWise

  1. Hammer DX, Liu Z, Cava JA, Carroll J, Saeedi O. On the axial location of Gunn’s dots. American journal of ophthalmology case reports. 2020 Sep 1;19:100757. https://doi.org/10.1016/j.ajoc.2020.100757
     
  2. Graham SL, Bennett L, Wechsler D. Patterns of ganglion cell loss, influence of scan area and OCT segmentation strategies in detection of glaucoma. Investigative Ophthalmology & Visual Science. 2016 Sep 26;57(12):849-.  
    https://iovs.arvojournals.org/article.aspx?articleid=2559650

Correspondence 

Dr Vinay Nangia
MS, FRCS, FRCOphth
Director 
Suraj Eye Institute
Nagpur
Email –education@surajeye.org

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