Ophthalmic Surgery, Lasers and Imaging Retina

Clinical Science 

Characterization of Artifacts Associated With Multicolor Confocal Scanning Laser Ophthalmoscopy

Henry L. Feng, MD; Sumit Sharma, MD; Sandra Stinnett, PhD; Sanjay Asrani, MD; Prithvi Mruthyunjaya, MD, MHS

Abstract

BACKGROUND AND OBJECTIVE:

To characterize the appearance of three types of artifacts observed on multicolor confocal scanning laser ophthalmoscopy (cSLO).

PATIENTS AND METHODS:

Retrospective review of 159 eyes of 96 consecutive patients from the Duke Eye Center who underwent multicolor cSLO with spectral-domain optical coherence tomography (SD-OCT). Infrared (IR), green, blue, and multicolor reflectance images were evaluated for artifacts with corresponding SD-OCT scans available for reference.

RESULTS:

Multicolor cSLO artifacts were detected in 23.3% (37 of 159) of eyes and comprised three main patterns: spot, wisp, and net. Only three instances of these artifacts were detected on IR reflectance versus 34, 37, and 35 instances on green, blue, and multicolor reflectance, respectively. Artifacts were observed in 0% of eyes with clear lenses, 27.7% of eyes with cataracts, and in 20.8% of eyes with posterior chamber intraocular lenses.

CONCLUSION:

Awareness of spot, wisp, and net artifacts when interpreting multicolor cSLO images may facilitate the identification of true retinal pathology.

[Ophthalmic Surg Lasers Imaging Retina. 2017;48:810–815.]

Abstract

BACKGROUND AND OBJECTIVE:

To characterize the appearance of three types of artifacts observed on multicolor confocal scanning laser ophthalmoscopy (cSLO).

PATIENTS AND METHODS:

Retrospective review of 159 eyes of 96 consecutive patients from the Duke Eye Center who underwent multicolor cSLO with spectral-domain optical coherence tomography (SD-OCT). Infrared (IR), green, blue, and multicolor reflectance images were evaluated for artifacts with corresponding SD-OCT scans available for reference.

RESULTS:

Multicolor cSLO artifacts were detected in 23.3% (37 of 159) of eyes and comprised three main patterns: spot, wisp, and net. Only three instances of these artifacts were detected on IR reflectance versus 34, 37, and 35 instances on green, blue, and multicolor reflectance, respectively. Artifacts were observed in 0% of eyes with clear lenses, 27.7% of eyes with cataracts, and in 20.8% of eyes with posterior chamber intraocular lenses.

CONCLUSION:

Awareness of spot, wisp, and net artifacts when interpreting multicolor cSLO images may facilitate the identification of true retinal pathology.

[Ophthalmic Surg Lasers Imaging Retina. 2017;48:810–815.]

Introduction

Multicolor confocal scanning laser ophthalmoscopy (cSLO) is a novel imaging modality on a commercially available optical coherence tomography (OCT) system (Spectralis; Heidelberg Engineering, Heidelberg, Germany) that utilizes three discrete lasers to simultaneously capture data from various structures of the ocular fundus. Infrared (IR) reflectance has the potential to visualize retinal pigment epithelium (RPE), drusen, and choroidal abnormalities. Green reflectance highlights hemorrhages and retinal vasculature, whereas blue reflectance produces detailed images of surface retinal pathology such as epiretinal membranes and nerve fiber layer defects.1,2 Recent studies aimed at characterizing specific retinal conditions on multicolor cSLO continue to elucidate the clinical applications of this technology.3,4 Despite these advances, experience with multicolor imaging remains relatively limited, and the interpretation of these images still requires thorough inspection in addition to cross referencing with other imaging techniques.2

The identification of artifacts associated with a novel imaging modality is clinically important to minimize interpretive errors that may generate undue concern. It is well-known that artifacts can appear on other modalities such as color fundus photography5 and spectral-domain OCT (SD-OCT);6 however, artifacts seen on multicolor cSLO are not well documented. Pang and Freund7 recently introduced hyperreflective “ghost maculopathy” as one artifact associated with near-IR and multicolor imaging that occurs in a proportion of pseudophakic patients. This study aims to characterize three additional artifacts that have been observed on multicolor cSLO to improve the utility and reliability of this novel imaging technique.

Patients and Methods

Patients

This retrospective study examined 159 eyes of 96 consecutive patients from the Duke Eye Center Retina and Glaucoma Service who underwent multicolor cSLO with SD-OCT during a single session over a 6-month period for a variety of retinal and optic nerve conditions. Prior approval was obtained from the Duke University Institutional Review Board and the requirement for informed consent was waived. This study complied with the Health Insurance Portability and Accountability Act of 1996 and followed the tenets of the Declaration of Helsinki.

Imaging Parameters

Fundus imaging was performed using the Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany). Settings used for image acquisition were similar to those described in our previous study involving multicolor imaging.8 Briefly, SD-OCT scans of the posterior pole (30° × 25° cube, 61 horizontal B-scans, automatic real-time [ART]9) were acquired using an 870 nm superluminescent diode during the same session as multicolor cSLO imaging. SD-OCT acquisition speed was 40,000 A-scans per second, with a scan depth of 1.9 mm, axial resolution of 3.87 μm, and lateral resolution of 11.68 μm under high-speed settings. Wavelengths for HRA+OCT multicolor cSLO were 488 nm, 518 nm, and 820 nm for the blue, green, and infrared scanning lasers, respectively. Multicolor cSLO scan angle was 30°, laser power 25%, and ART 25. Pseudo-color channels, contrast, brightness, and sharpening parameters were not altered manually in any of the images evaluated in this study.

Two retina specialists (PM, SS) and a glaucoma specialist (SA) identified atypical patterns or artifacts after evaluating IR, green, blue, and multicolor cSLO images with corresponding SD-OCT scans available for reference. Descriptive statistics were performed to determine the frequency of artifacts identified on SD-OCT and on each laser reflectance image.

Results

Multicolor cSLO artifacts were detected in 23.3% of eyes (37 of 159) and were divided into three patterns (spot, wisp, and net artifacts) observed on IR, green, blue, and multicolor reflectance images (Table). In all eyes where an artifact was observed on cSLO imaging, no corresponding hyper- or hyporeflective foci were detected on SD-OCT, and no corresponding abnormalities were documented on dilated fundus exam performed by a trained expert.

Artifact Frequency on Multicolor Imaging

Table:

Artifact Frequency on Multicolor Imaging

Spot artifacts were most frequently visualized on blue reflectance as circular hyporeflective foci with well-circumscribed hyperreflective borders (Figure 1) often located within the macula. There was minimal interindividual variability in the morphology, reflectivity, and location of these spots. Wisp artifacts were observed with equal frequencies on green, blue, and multicolor reflectance, appearing as curvilinear hyperreflective filaments with some variability in thickness (Figure 2). Net artifacts were most frequently observed on blue and multicolor reflectance as a hyperreflective reticular lattice of polygonal rings (Figure 3). Overall, the fewest number of artifacts were detected on IR reflectance.

The appearance of spot artifacts on infrared (IR), green (G), blue (B), and multicolor (MC) reflectance with corresponding spectral-domain optical coherence tomography.

Figure 1.

The appearance of spot artifacts on infrared (IR), green (G), blue (B), and multicolor (MC) reflectance with corresponding spectral-domain optical coherence tomography.

The appearance of wisp artifacts on infrared (IR), green (G), blue (B), and multicolor (MC) reflectance with corresponding spectral-domain optical coherence tomography.

Figure 2.

The appearance of wisp artifacts on infrared (IR), green (G), blue (B), and multicolor (MC) reflectance with corresponding spectral-domain optical coherence tomography.

The appearance of net artifacts on infrared (IR), green (G), blue (B), and multicolor (MC) reflectance with corresponding spectral-domain optical coherence tomography.

Figure 3.

The appearance of net artifacts on infrared (IR), green (G), blue (B), and multicolor (MC) reflectance with corresponding spectral-domain optical coherence tomography.

Lens status was associated with detected artifacts. Overall, the lens was characterized as being clear in 13.8% of eyes (22 of 159), with any detectable cataract in 40.9% of eyes (65 of 159), and with a posterior chamber intraocular lens (PC-IOL) in 45.2% of eyes (72 of 159). No eyes had an anterior chamber intraocular lens in our study. Of the 72 eyes with PC-IOL's, 18% (13 of 72) had some degree of posterior capsular opacification (PCO), and 20.8% (15 of 72) had an open posterior capsule. No artifacts were detected in eyes with clear lenses. A total of 23 artifacts (12 spot, three wisp, and seven net) were observed in 27.7% of eyes (18 of 65) with cataracts, and a total of 15 artifacts (seven spot, one wisp, and seven net) were observed in 20.8% of eyes (15 of 72) with PC-IOL's. Three spot artifacts were detected in 23.1% of eyes (three of 13) with PCO, and two artifacts (one spot, one wisp) were detected in 13.3% of eyes (two of 15) with an open posterior capsule.

In several instances, repeated acquisitions were conducted during a single imaging session after allowing the patient to blink. The successive images revealed a combination of shifting in artifact location, attenuation of prior artifacts, as well as the emergence of new artifacts (Figure 4). In some cases, artifacts were completely eliminated in successive images.

Blue reflectance images demonstrating changes in spot (1A and 2A) and net (1B and 2B) artifacts after patient blinking.

Figure 4.

Blue reflectance images demonstrating changes in spot (1A and 2A) and net (1B and 2B) artifacts after patient blinking.

Discussion

Multicolor cSLO technology is an adjunctive imaging technology that provides a pseudo-color representation of the fundus to complement cross sectional OCT imaging. Recognizing imaging artifacts is important for the clinician to accurately identify disease pathology. We have identified three new artifacts associated with multicolor cSLO imaging (wisp, spot, and net) in nearly a quarter of imaged eyes. IR reflectance, a more commonly utilized imaging modality, had the lowest prevalence of spot, wisp, and net artifacts. Notably, only three instances of these artifacts were detected on IR reflectance versus 34, 37, and 35 instances on green, blue, and multicolor reflectance, respectively. This difference in frequency of observed artifacts with the newer multicolor cSLO technology highlights the importance of recognizing artifacts to avoid confusing such findings for true pathology.

Although cSLO is less prone to light scattering than color fundus photography, light must still pass through multiple ocular media prior to reflection and ultimately detection. Thus, the origin of spot, wisp, and net artifacts may arise from any potential sources of light scattering along the laser's path. It is well-known that colloidal light scattering is more pronounced at lower wavelengths of the visible spectrum. Given that none of the artifacts were detected in phakic eyes with clear lens status, it is possible that the presence of cataracts or a PCIOL increases the scattering of green and blue wavelengths relative to IR wavelengths.

The artifacts observed in this study also changed or disappeared with patient blinking and consecutive imaging. This suggests that these new artifacts may also be derived from tear film light scattering that is more pronounced in the blue and green wavelengths. As a result, patients with an irregular tear film may be more prone to developing the artifacts described in this study. Taken together, it is possible that patients with clear lenses also have a lower incidence of corneal abnormalities, which may account for the lack of artifacts seen in eyes with clear lenses.

Although we did not have color fundus photographs for comparison, the absence of corresponding findings on dilated fundus exam performed by a trained expert and changes in appearance with serial imaging support the artefactual nature of these findings on multicolor cSLO. Although the experienced clinician may easily recognize protruding eyelashes or motion abnormalities as benign, artifacts that mimic true findings risk being misinterpreted and could potentially result in unnecessary concern, superfluous diagnostic testing or improper management. Macular spot artifacts can colocalize with other true pathologic processes. For example, we have previously described the development of hyporeflective spots in the macula that appeared in four eyes following pars plana vitrectomy with internal limiting membrane peeling.8 However, these irregularities correlated precisely with well-demarcated inner retinal defects on SD-OCT (Figure 5). In contrast to spot artifacts, the morphology of these true inner retinal alterations is ovoid rather than round, and the lesions appear to follow the nerve fiber layer in an arcuate distribution.8–11 Additionally, the evaluation of epiretinal membranes, which are typically well visualized on multicolor cSLO,4 may be confounded by superimposed net artifacts that obscure the degree and extent of pathology.

Blue reflectance images of inner retinal alterations (A) with corresponding spectral-domain optical coherence tomography (SD-OCT) compared to spot artifacts (B) with corresponding SD-OCT.

Figure 5.

Blue reflectance images of inner retinal alterations (A) with corresponding spectral-domain optical coherence tomography (SD-OCT) compared to spot artifacts (B) with corresponding SD-OCT.

Awareness of spot, wisp, and net artifacts on multicolor cSLO will facilitate more accurate interpretations of multicolor images and reduce the likelihood of further unnecessary clinical testing.

References

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Artifact Frequency on Multicolor Imaging

FindingSD-OCT (%)IR (%)G (%)B (%)MC (%)
Spot Artifact0 (0)2 (1.3)17 (10.7)19 (11.9)17 (10.7)
Wisp Artifact0 (0)1 (0.6)4 (2.5)4 (2.5)4 (2.5)
Net Artifact0 (0)0 (0)13 (8.2)14 (8.8)14 (8.8)
Authors

From Rutgers Robert Wood Johnson Medical School, Piscataway, NJ (HLF); Duke Eye Center, Duke University, Durham, NC (HLF, S Sharma, S Stinnett, SA, PM); Cole Eye Institute, Cleveland Clinic Foundation, Cleveland (S Sharma); and Byers Eye Institute, Stanford University, Palo Alto, CA (PM).

Dr. Asrani receives lecture honoraria from Heidelberg Engineering. The remaining authors report no relevant financial disclosures.

Address correspondence to Prithvi Mruthyunjaya, MD, MHS, Byers Eye Institute at Stanford, 2462 Watson Court, Palo Alto, NC 94303; email: Prithvi9@Stanford.edu.

Received: January 30, 2017
Accepted: July 19, 2017

10.3928/23258160-20170928-05

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