Spark ImageWise 41

Cotton wool spots

Dr. Rashmi Nagar, Dr. Prabhat Nangia, Dr. Sarang Lambat, Dr. Vinay Nangia 
Suraj Eye Institute, 559, New Colony, Sadar, Nagpur- 440001.

Case Description:
A male 71 years of age, came with complaints of blurring of vision in both eyes for a duration of 1 year. He was a known case of Diabetes mellitus. His best corrected visual acuity was 6/18, N10 in the right eye (RE) and 6/9, N6 in the left eye (LE). Slit lamp examination showed grade 1 nuclear sclerosis in both eyes. Intra-ocular pressure on Goldman applanation tonometry was found to be 18 mmHg in both eyes.
Fundus examination revealed posterior polar cotton wool spots (CWS) with dot and blot hemorrhages in both eyes. Few flame-shaped hemorrhages were also seen in the LE.

Figure 1 – Colour fundus photograph of RE shows a large cotton wool spot (red arrow) which is seen causing an RNFL defect (blue arrows) and another resolving cotton wool spot (yellow arrow) which is causing the beginning of an RNFL defect just adjacent to it (black arrow), not reaching the disc.
Figure 2 – Colour fundus photograph of LE shows cotton wool spots (red arrows), dot and blot hemorrhages (yellow arrows), flame shaped hemorrhages (green arrows) and a vertical cup to disc ratio (VCDR) of 0.4
Figure 3– Spectral Domain OCT (SD-OCT) circumpapillary RNFL (pRNFL) scan of RE (A) shows normal RNFL.
Figure 4– SD-OCT pRNFL scan of left eye (OS) shows RNFL thinning (B – yellow arrows and D – red arrows).
Figure 5 – Right eye – Line scan through the cotton wool spot shows edema of the RNFL (A and B – yellow arrows).
Figure 6 – Right eye – Line scan through the same spot (A and B – yellow arrows) shows RNFL damage along with ischemia of the inner retinal layers (B – red arrows).
Figure 7 – Left eye – Line scan through the cotton wool spot shows edema of the RNFL (A and B – yellow arrows).
Figure 8
– Left eye – Line scan through the same spot (A and B – yellow arrows) shows RNFL damage along with ischemia of the inner retinal layers (B – red arrows).

Discussion:
         
Cotton wool spots are non-specific and occur in many retinal vascular conditions. They are localized accumulations of axoplasmic debris within adjacent bundles of ganglion cell axons, and are thought to occur after arteriolar occlusion at the borders of large ischemic areas.1 Our patient was a diabetic and we would expect cotton wool spots in diabetic patients. While it has been stated that cotton wool spots may not be considered to be retinal nerve fiber layer infarcts, we may point out the clinical findings in our subject relative to cotton wool spots.

Fig. 1. shows a red arrow indicating a bright large cotton wool spot.  As we trace this area to the optic disc, we do see a classical retinal nerve fiber layer defect delineated with cyan arrows. Below this CWS is another smaller CWS which is relatively pale (Fig. 1. yellow arrow). Just adjacent to this is an area indicated by a black arrow where can just make out the loss of RNFL which has not reached the disc as yet.

In Fig 4.B – yellow arrow and Fig. 4.D – red arrow indicates the swelling of the RNFL since the line scan passes adjacent to the cotton wool spot seen in Fig 4.A – cyan arrow. 

It is apparent that cotton wool spots are significantly indicative of ischemia. It is also evident, that there must be considerable damage to the ganglion cells, causing retrograde axonal loss as seen clinically with evident RNFL loss in Fig. 1 (cyan arrows). We further did repeat scans of both eyes over a period of 5 months since the patient came with decreased vision in both eyes associated with macular oedema. 

Right eye SD-OCT line scan through the cotton wool spot shows a relatively hyper-reflective oval area involving all the inner retinal layers and impinging on the outer nuclear layer (Fig. 5 A and B – yellow arrows). It is reasonably well demarcated. The retina peripheral to this shows some thinning clinically. On follow-up scan 5 months later, (Fig. 6 A and B – yellow arrows) we find that the size of the cotton wool spot has reduced, however the ischemia related changes peripheral to the CWS have increased showing thinning of inner retinal layers (Fig. 6 B – red arrows). Left eye SD-OCT line scan through the cotton wool spot shows the initial appearance of the CWS (Fig. 7 A and B – yellow arrow) and Fig 8 (A and B yellow arrows) shows the changes in the CWS spots and the ischemic area (Fig. 8 B – red arrows) peripheral to it at 5 months follow–up. 

It is evident that CWS are indicative of significant ischemia. These patients may not be lost to follow up and should be followed up on a regular basis, especially in view of the possible changes that may result with devastating consequences for the macula if the cotton wool spots are close to it and also for the retinal as a whole. CWS may be a harbinger of bad news for our patients and for us.

Readwise:

  1. McLeod D. Why cotton wool spots should not be regarded as retinal nerve fibre layer infarcts. British Journal of Ophthalmology. 2005 Feb 1;89(2):229-37. 10.1136/bjo.2004.058347
  2. Gomez ML, Mojana F, Bartsch DU, Freeman WR. Imaging of long-term retinal damage after resolved cotton wool spots. Ophthalmology. 2009 Dec 1;116(12):2407-14. https://doi.org/10.1016/j.ophtha.2009.05.012

Correspondence

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

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