A 46 year old Caucasian female was referred in to the office from a colleague for evaluation of visual disturbances in the right eye more so than the left. She first noticed this approximately 3 months earlier, and the visual disturbance has remained stable. She described the problem as a yellowish ‘blind spot’ slightly to the right of fixation. During her evaluation with the first provider, Amsler grid testing did demonstrate some metamorphopsia OD. At the same time, she was noting an increase in the frequency of her headaches, along with the onset of some right sided ear and jaw pain. After evaluation evaluated by her PCP, she was referred to ENT and for an MRI. The MRI was normal, and the ENT visit happened to coincide with the day of our first visit, having seen the ENT first who diagnosed TMJ right side greater than left. Other than oral contraceptives and ibuprofen PRN, she was taking no medications and reported no allergies to medications. Given her demographics and some ‘normal’ stressors in her life, a tentative diagnosis of CSR was made based upon the history.

At the visit to my office the first day, visual acuities were 20/20-1 OD and OS. Pupils were ERRLA and there was no afferent pupillary defect. Applanation tensions were 14mmHg OD and 15 mmHg OS at 4:14PM. A slit lamp examination of the anterior segments was unremarkable.

The patient was dilated in the usual fashion and macular OCT images were obtained. They showed no evidence at all of CSR, nor any other overt retinal pathology. Her optic nerves were healthy with plush, well perfused neuroretinal rims. The retinal vasculature was unremarkable, as were the crystalline lenses and the peripheral retinas. Given the lack of OCT findings consistent with metamorphopsia, the patient was scheduled for threshold field studies the following morning.

24-2 visual fields were preformed as directed the following morning, and there were some scattered central defects seen OS>OD, none of which respected the vertical nor horizontal midlines. Given the history of having had a normal MRI, I asked the patient to pick up the MRI scans (CD form) from the imaging center, and bring them back to me for my review. I also asked that the visual field studies be repeated. The patient complied with these requests, and the follow up 24-2 visual fields were similar to the first set of fields, though both central defects were less pronounced and were not indicative of bilateral prechiasmal lesions, nor chiasmal or retro chiasmal lesions. When I reviewed the MRI images, the only item I noted that was not in the radiology report was a partially empty sella. All else looked normal to me, but radiology is not my specialty. A quick phone call to the radiology department and a review by the interpreting radiologist confirmed all was in fact normal. He did mention that the sella was consistent with partial empty sella findings, which are normal in a perimenopausal woman.

Hummmmm…..The retina looks fine. The optic nerves look fine, the neuroimaging looks fine, pupils are fine, but there is a visual defect.

Let’s run a 3rd visual field, this time a 10-2 threshold strategy, and reassess the OCT’s again, this time using a neuro profile. The neuro profile OCT scans on the Heidelberg Spectralis do a couple of things differently. First is the fact that the RNFL circle scans of 3 different diameters stratify out the papillomacular bundle, emphasizing those fibers that are often affected in optic nerve disorders. And secondly, the macular scans are vertically oriented, rather than the traditional horizontal scans.

The 10-2 visual field demonstrated similar non neurological field deficits, similar to the first two sets of field studies. On close examination of the OCT scans this day, the problem became evident. And actually, truth be told, these findings were consistent with the clinical findings and history to this point:acute macular neuroretinopathy.

AMN is a condition that is usually unilateral that typically affects younger women. Its etiology has not been fully elucidated, but it is believed to be a result of microvascular focal ischemia in areas of the deep retinal capillary plexus due to microthrombosis. This proposed microthrombosis has been associated with autoimmune disorders, as well as following COVID 19 infections as well as following COVID 19 vaccinations1. The visual defects may last for months or be permanent.

Given the involvement of the deep capillary plexus, the OCT findings are found in the outer plexiform layer, as shown in Figure 1 below. Note in particular how subtle these findings are, and therefore relatively easily missed on quick OCT review. Your first view of the scans in Figure 1 will most likely elicit a response from you that they look normal. And it does, but not exactly. Also note that in Figure 1, we are looking at the first set of OCT scans taken of this patient, which are the traditional horizontally oriented scans. On quick view, it does in fact appear normal.

Figure 1: This is the first OCT image obtained of the patient’s left eye. Note the relatively normal findings. Anatomically, this B scan was obtained slightly superior to the foveal center.

What defect you ask? The tip off was the neuro OCT macular scan, where the B scans are taken vertically. On close viewing of those scans, since you are essentially comparing anatomy above and below the horizontal raphe, the asymmetry between the superior deep retinal plexus and that of the inferior deep retinal plexus temporal to the fovea was obvious.

Figure 2 below is the same exact scan as Figure 1, but with the affected area identified by the red circle. Note the hyperintensity of the focal edema associated with AMN. It is subtle no doubt, but it is definitely present. Of course in this scan, we are comparing nasal and temporal (to the fovea) layers of the retina, and there are normally anatomical differences between them, especially in the RNFL. The defect is classic with AMN, as is the history and the findings.

Figure 2 is the same image as Figure 1, but with the area of hyperintensity of the outer plexiform layer, which is believed to be focally ischemic in AMN.

Fundus autofluorescence is sometimes helpful in identifying this condition, as can be fluorescein angiography and OCT angiography.

This condition is similar to PAMM (paracentral acute middle maculopathy), though PAMM typically affects the inner nuclear layer (INL) as opposed to the outer plexiform layer (OPL). Both PAMM and AMN are believed to be related to each other and are indicative of microthrombosis. They may be manifestations of the same disease1,2.

Figure 3 is the OCT A through the OPL layer. Note the asymmetry of the vascular density above as opposed to below the horizontal raphe adjacent to the fovea.

Subtle retinal findings such as those seen in AMN and PAMM are often impossible to see in vivo, and can also be challenging to identify even with OCT imaging. They are subtle, and close scrutiny of various OCT segments/scans is crucial to finding these lesions, as a single scan printout may very well not show these defects at all. Great image acquisition and high resolution OCT scanning can make all the difference in subtle findings such as these.

By and large, from a disease perspective, OCT has played its biggest role in the posterior segment. In retinal and in particular macular diseases, the utilization of OCT technology has played a huge role in improving visual outcomes.

Some conditions are readily visible clinically in vivo, such as macular edema, and those conditions are confirmed, quantified and modified with OCT imaging. But sometimes, there are subtle conditions that are simply not seen without OCT technology assisting in the evaluation. And even then, some of those conditions are very subtle, as in this case of AMN.

While initially this seemed as though this would be a straightforward case of CSR, being able to adapt and consider other differentials is always important in clinical care. Having the technology to evaluate the patient certainly helps as well. Instead of CSR in the right eye, AMN was found in the left eye, affecting the visual field just right of fixation, leading the patient, and me initially, to believe the problem was in the right eye.

 

REFERENCES:

1. Munk M, et al. New associations of classic acute macular neuroretinopathy. Br J Ophthalmol 2015; 306845.

2. Yu S, et al. The spectrum of superficial and deep capillary ischemia in retinal artery occlusion. Am J Ophthalmol 2015;159(1):53–63.e1-2.