Comparison of optical coherence tomography findings in a patient with central retinal artery occlusion in one eye and end-stage glaucoma in the fellow eye.

This case describes a patient with chronic central retinal artery occlusion in one eye and end-stage traumatic glaucoma in the fellow eye. Optical coherence tomography (OCT) of the macula of the chronic phase of central retinal artery occlusion of the right eye indicated loss of the normal foveal depression, extensive inner retinal atrophy, and marked retinal thinning. In contrast, scans of the left eye with end-stage glaucoma demonstrated an intact foveal depression and limited retinal thinning. The pattern of macular OCT findings in this patient illustrates distinguishing features between chronic central retinal artery occlusion and chronic optic neuropathy due to end-stage glaucoma.

INTRODUCTION

Previous studies have highlighted the distinguishing characteristics of macular optical coherence tomography (OCT) of central retinal artery occlusion (CRAO) and chronic optic neuropathy (CON).1–4 Typical macular OCT findings of late-stage CRAO include extensive inner retinal atrophy, loss of the normal foveal depression, loss of the normal stratification of the inner retinal layers, and significant thinning of the retina. In contrast, CON is characterized by relative preservation of the foveal depression and stratification of the inner retinal layers, only limited atrophy of the inner retina, and mild thinning of the retina.1 However, these studies used comparative groups of different patients, unlike this educational case where the two conditions presented in the same patient representing, to our knowledge, the only case with an internal control in peer reviewed literature.

CASE REPORT

A 72-year-old male with non-insulin-dependent diabetes mellitus, hyperlipidemia, and a previous endarterectomy for occlusion of the left carotid artery presented for evaluation. His past ophthalmologic history included exotropia, penetrating traumatic glaucoma resulting in pseudophakia in the left eye, bilateral diabetic retinopathy with bilateral macular edema, and panretinal photocoagulation of the right eye. The penetrating trauma occurred approximately 50 years prior to presentation when he sustained an intraocular metallic foreign body in his left eye that was treated with emergent lensectomy and sector iridectomy. He remained aphakic with a visual acuity of 20/400 in the left eye until age 61 when a posterior chamber intraocular lens was implanted, improving his visual acuity to 20/40. Significant visual field defects and optic nerve head cupping were seen on examination, and the patient was diagnosed with traumatic glaucoma secondary to the remote metallic foreign body injury managed with ophthalmic medications and Baerveldt tube implantation. At the time of presentation, visual acuity of the left eye was 20/80 and his glaucoma reached end-stage with an almost total cupping, a residual island of central visual field, and a relative afferent pupillary defect.

Two years prior to presentation, the patient developed superior hemiretinal vein occlusion (HRVO) with cystoid macular edema in the right eye. Immediately following the occlusion, the visual acuity of the right eye decreased from 20/30 to 20/400, and significant edema was noted on exam and on OCT scans (central subfield macular thickness was 651 μm). He received three intravitreal injections of bevacizumab as well as focal macular laser, resulting in a significant improvement in macular edema (224 μm) and visual recovery (20/100). No evidence of glaucoma was present in the right eye prior to the HRVO event, as demonstrated by the absence of suggestive findings on visual field testing or optic nerve head findings on funduscopy.

Several months after resolution of HRVO, the patient experienced sudden visual loss in the right eye due to acute CRAO that manifested with retinal whitening, a cherry-red spot, and delayed arterial filling on fluorescein angiography. Immediate anterior chamber paracentesis was performed and intravenous tissue plasminogen activator was administered, but vision did not recover. During the process, the patient was evaluated with macular OCT of both eyes before the onset of acute CRAO [Figure 1] and upon follow-up visits [Figure 2], allowing for comparison of the macular OCT findings between chronic CRAO and CON due to end-stage glaucoma.

Figure 1

Stratus time domain optical coherence imaging prior to onset of central retinal artery occlusion in the right eye. (a) Preservation of the stratification of the inner retinal layers is noted in the right eye, and the central subfield thickness measures 224 μm. (b) In the left eye, the inner retinal layers are collapsed into a single thick hyperreflective band bordered externally by the hyporeflective inner nuclear layer. The central subfield thickness measures 231 μm. Note intact foveal depression in both eyes despite end-stage glaucoma in the left eye

Figure 2

Spectralis spectral domain optical coherence imaging and funduscopy 16 months following central retinal artery occlusion. (a) Note the absence of foveal depression and stratification of inner retinal layers in the right eye. The inner retina is collapsed into a single thick hyperreflective band. The central subfield thickness measures 204 μm. (b) Left eye discloses similar features to those shown in figure 1b, and the central subfield thickness is 284 μm. (c) Retinal nerve fiber layer (RNFL) analysis of both eyes. Note the marked decrease in RFNL thickness of both eyes. (d) Right eye fundus photograph shows narrowed arterioles, scarring secondary to panretinal and macular photocoagulation, optociliary shunt vessels, and absence of optic nerve head cupping. (e) Left eye fundus photograph shows nearly complete optic nerve head cupping with relative preservation of the retinal vascular caliber

In the right eye, a third-generation time domain OCT (TD-OCT Zeiss Stratus, Model number 3000, Carl Zeiss AG, Jena, Germany) was performed prior to the acute CRAO. Stratus TD-OCT demonstrated a central subfield (CSF) thickness of 224 μm (the normal CSF thickness on Stratus TD-OCT was 212±20 μm),5 as well as an intact foveal depression [Figure 1a]. Four months after the retinal artery occlusion, Stratus TD-OCT yielded a CSF thickness of 162 μm and demonstrated significant retinal thinning and loss of the foveal depression. In the left eye, several Stratus TD-OCT studies prior to presentation demonstrated an intact foveal depression despite end-stage glaucoma [Figure 1b], and the CSF thickness ranged from 213 μm to 260 μm.

Spectral domain OCT (SD-OCT, Heidleberg HRA-OCT Spectralis, Heidelberg Engineering, Inc., Vista, CA, USA) was performed 16 months following the acute event. The CSF thickness measurements were 204 and 284 μm in the right and left eyes, respectively (the normal CSF thickness value on Spectalis SD-OCT was 270±22 μm),6 consistent with the thickness disparity between the two eyes shown on Stratus TD-OCT. In addition, extensive retinal thinning with loss of stratification of the inner retinal layers and the foveal depression was noted in the right eye [Figure 2a], in contrast to the left eye where relative preservation of the stratification of the inner retinal layers and the foveal depression was evident [Figure 2b]. Diffuse retinal nerve fiber layer (RNFL) loss was evident in both eyes but was worse in the right [Figure 2c]. The global average value was 26 μm in the right eye and 53 μm in the left. At the time of the most recent OCT assessment, the visual acuity remained stable in the left eye (20/80), while the visual acuity of the right eye had not improved (2/200 E) since the occlusive event. Fundus photographs of the right eye revealed narrowed arterioles secondary to the occlusive event, panretinal and macular photocoagulation scars, optociliary shunt vessels, and absence of optic nerve head cupping [Figure 2d]. In the left eye, significant optic nerve head cupping with relative preservation of the retinal vascular caliber is evident, consistent with the diagnosis of glaucoma [Figure 2e].

Of note is that, with respect to the quantitative OCT data obtained, all line scans were reviewed for edge detection errors particularly in the CSF. A study was deemed unreliable when more than two out of six macular line scans included edge detection errors within the CSF. Regarding qualitative OCT data such as the stratification of the retinal layers, retinal atrophy and the contour of the foveal depression, only line scans with good signal strength allowing for adequate interpretation of such data were analyzed.

DISCUSSION

The pattern of macular OCT findings in this patient exemplifies the distinguishing features of CRAO and CON described by Ghazi et al.1 Results from the patient's recent SD-OCT scans of the right eye [Figure 2a] closely match those of the TD-OCT found in the chronic CRAO group from that study. As noted above, the patient was also followed with TD-OCT following CRAO which, similar to SD-OCT studies, demonstrated a substantial decrease in central subfield thickness (162 μm). However, the SD-OCT CSF thickness value was significantly higher in comparison (204 μm). This apparent discrepancy between post-CRAO CSF thickness values is explained by the distinct measurement protocols used by each system's software, with the Spectralis OCT typically calculating higher CSF values than Stratus OCT.56

The patient developed CRAO and end-stage traumatic glaucoma in eyes that are developmentally and genetically similar. Each of the patient's eyes, therefore, serves as a control for the other and further validates the use of OCT in differentiating chronic CRAO from CON. This case thus demonstrates that extensive inner retinal atrophy with disruption of the normal stratification of the inner retinal layers, loss of the normal foveal depression, and marked thinning of the retina are findings of chronic CRAO as opposed to CON, where the atrophic changes of the inner retina are limited and the foveal depression is preserved.

These differentiating OCT features are a reflection of the specific blood supply and the distinct changes in retinal histology that occur in chronic CRAO and CON. Since the central retinal artery and its branches supply only the inner retina, the atrophy and loss of stratification seen in chronic CRAO is limited to this layer of the retina and does not extend to the outer retina, which receives its blood supply from choroidal circulation. The disappearance of the foveal depression on OCT occurs because loss of the inner retina in chronic CRAO also involves the para-foveolar slope, leaving intact only the outer layers of the foveola itself. In contrast to chronic CRAO, inner retinal atrophy seen in optic neuropathy is limited to the nerve fiber and ganglion cell layers. Therefore, macular OCT demonstrates milder retinal thinning and relative preservation of the foveal depression and stratification of the inner retinal layers [Figure 2b].

The patient's remote ophthalmic history of bilateral diabetic retinopathy with associated diabetic macular edema, along with his more recent history of HRVO in the right eye treated by macular laser therapy and subsequent intravitreal bevacizumab injections for associated macular edema, represent potential confounders for the macular OCT findings in that eye. However, the chronology of events demonstrates that the macular thinning was unrelated to the diabetic macular edema or to the resolution of the HRVO and macular edema following treatment, and that it occurred only following the onset of the acute CRAO episode. The Stratus TD-OCT scan of the right eye shown in Figure 1a was performed several months after the patient's final treatment with bevacizumab for macular edema and just one month prior to the onset of CRAO. At this time, TD-OCT displayed a normal CSF thickness with preservation of the inner retina and foveal depression. The CSF thickness drastically decreased following the CRAO event with associated loss of the inner retina and foveal depression as seen in Figure 2a. In addition, previous studies have suggested that macular atrophy as imaged by OCT is unlikely to result from prior treatments of macular edema in venous occlusive disease.78

CRAO and chronic optic neuropathy are most often diagnosed based on history and exam findings such as optic nerve appearance. In CRAO, for example, pallor of the nerve is commonly seen, whereas CON associated with glaucoma demonstrates progressive cupping of the disc. However, some patients with CRAO may be difficult to diagnose on clinical grounds alone, especially in the absence of retinal vascular emboli.9 These cases may be confused with certain types of CON (especially those that rarely display optic disc cupping such as nonarteritic anterior ischemic optic neuropathy10 ) due to similarities in clinical features including visual acuity and field loss, an afferent pupillary defect, and funduscopic findings such as optic nerve head pallor and vascular thinning. Macular OCT findings as described here may differentiate between chronic CRAO and CON in challenging situations. This, in turn, may guide the diagnostic work-up and treatments that are drastically different between the two entities.