Identifying and understanding optical coherence tomography artifacts that may be confused with glaucoma / Identificando e compreendendo os artefatos de tomografia de coerência óptica que podem ser confundidos com o glaucoma

ABSTRACT Optical coherence tomography is often used for detection of glaucoma as well as to monitor progression. This paper reviews the most common types of artifacts on the optical coherence tomography report that may be confused with glaucomatous damage. We mainly focus on anatomy-related artifacts in which the retinal layer segmentation and thickness measurements are correct. In such cases, the probability maps (also known as deviation maps) show abnormal (red and yellow) regions, which may mislead the clinician to assume disease is present. This is due to the anatomic variability of the individual, and the normative database must be taken into account.

RESUMO A tomografia de coerência óptica é frequentemente usada para detectar glaucoma, bem como para monitorar a progressão. Este artigo analisa os tipos mais comuns de artefatos no relatório de tomografia de coerência óptica que podem ser confundidos com danos glaucomatosos. Nós nos concentramos principalmente nos artefatos relacionados à anatomia em que a segmentação da camada da retina e as medidas de espessura estão corretas. Nesses casos, os mapas de probabilidade (também conhecidos como mapas de desvio) mostram regiões anormais (vermelho e amarelo), o que pode induzir o clínico em erro ao supor que a doença está presente. Isto se deve à variabilidade anatômica do indivíduo, e o banco de dados normativo deve ser levado em conta.

The Association Between Clinical Features Seen on Fundus Photographs and Glaucomatous Damage Detected on Visual Fields and Optical Coherence Tomography Scans.

PURPOSE: To classify the appearance of the optic disc seen on fundus photographs of healthy subjects and patients with or suspected glaucoma whose diagnosis was based upon visual fields (VFs) and spectral-domain optical coherence tomography (sdOCT) results. PATIENTS AND METHODS: One eye of 100 patients with or suspected glaucoma and 62 healthy subjects were prospectively tested with 24-2 and 10-2 VF and macular and disc sdOCT cube scans. All eyes with or suspected glaucoma had a 24-2 mean deviation better than -6.0 dB and an abnormal appearing disc on stereophotographs. The retinal ganglion cell plus inner plexiform layer (RGC+) from the macular scans and the retinal nerve fiber layer (RNFL) from the macular and disc scans were segmented and converted to probabilities plots. An eye was considered "glaucoma" if the sdOCT probability plots showed an abnormality in a region that corresponded to a defect seen on the 24-2 and/or 10-2 VF total deviation plot. Similarly, an eye was considered "suspect" only if both the sdOCT and VF plots were normal. Healthy subjects (normal VFs and sdOCT) were classified as "controls" and used as reference for comparisons. Glaucoma specialists reviewed the stereophotographs and classified eyes based on the presence of signs suggestive of glaucomatous optic neuropathy. RESULTS: The pattern of clinical signs of glaucomatous optic neuropathy seen on stereophotographs was statistically different between glaucoma (P<0.001) and suspects (P<0.001) vs. controls and explained up to 68% of the total variance of the diagnosis based upon sdOCT and VFs. Vertical cup-to-disc>0.6, focal neuroretinal rim thinning, focal RNFL loss, and violation of the ISNT rule had the best performance to differentiate glaucoma and suspects from controls. Compared with the suspect group, glaucoma eyes (abnormal sdOCT and VF tests) were more likely to have vertical cup-to-disc>0.6 (92% vs. 69%, P=0.003), diffuse rim (53% vs. 9%, P<0.001) and RNFL (61% vs. 26%, P<0.001) thinning, and ß-zone parapapillary atrophy (68% vs. 17%, P<0.001). CONCLUSIONS: Focal and diffuse signs of glaucoma damage seen on stereophotographs often match damage shown on VFs and sdOCT. In addition, damage shown on VFs and sdOCT is often missed during clinical evaluation. Longitudinal studies ought to differentiate focal signs of glaucoma damage seen on stereophotography from false-positives or very early loss.

Evaluation of inner retinal layers in eyes with temporal hemianopic visual loss from chiasmal compression using optical coherence tomography.

PURPOSE: We measured macular inner retinal layer thicknesses using frequency-domain optical coherence tomography (fd-OCT) and correlated these measures with visual field (VF) in eyes with temporal hemianopia from chiasmal compression and band atrophy (BA) of the optic nerve. METHODS: Macular fd-OCT scans and VFs were obtained from 33 eyes of 33 patients with temporal hemianopia and 36 control eyes. The macular retinal nerve fiber layer (mRNFL), combined retinal ganglion cell and inner plexiform layers (RGCL+), and the inner nuclear layer (INL) were segmented. Measurements were averaged for each macula quadrant. Scans were assessed qualitatively for microcysts in the INL. The VF was estimated from the central 16 test points. The two groups were compared. Correlations between VF and OCT measurements were assessed. RESULTS: The mRNFL, RGCL+, and total retinal (TR) macular thickness measurements were significantly smaller in BA eyes than controls. In the nasal quadrants, INL measurements were significantly greater in BA eyes than controls. The mRNFL and RGCL+ measurements had greater discrimination ability than TR measurements in the temporal quadrants. A significant correlation was found between most OCT parameters and their corresponding VF parameters. The strongest association was observed between RNFL and RGCL+ thickness, and VF loss in the corresponding area. The INL microcysts were found in seven eyes with BA, but not in controls. CONCLUSIONS: Band atrophy leads to mRNFL and RGCL+ thinning, and INL thickening, and mRNFL and RGCL+ measurements are correlated strongly with VF loss. Segmented macular thickness measurements may be useful for quantifying neuronal loss in chiasmal compression.

Pattern electroretinogram in neuromyelitis optica and multiple sclerosis with or without optic neuritis and its correlation with FD-OCT and perimetry.

PURPOSE: To evaluate the ability of transient pattern electroretinogram (PERG) parameters to differentiate between eyes of patients with neuromyelitis optica (NMO), longitudinally extensive transverse myelitis (LETM), multiple sclerosis with optic neuritis (MS + ON), multiple sclerosis without optic neuritis (MS - ON), and controls, to compare PERG and OCT with regard to discrimination ability, and to assess the correlation between PERG, FD-OCT, and visual field measurements (VFs). METHODS: Visual field measurements and full-field stimulation PERGs based on both 48- and 14-min checks were obtained from patients with MS (n = 28), NMO (n = 20), LETM (n = 18), and controls (n = 26). In addition, FD-OCT peripapillary retinal nerve fiber layer (RNFL) and segmented macular layer measurements were obtained and their correlation coefficients were determined. RESULTS: Compared to controls, PERG amplitude measurements were significantly reduced in eyes with NMO and MS + ON, but not in eyes with LETM and MS - ON. PERG amplitudes were significantly smaller in NMO and MS + ON eyes than in MS - ON eyes. PERG and OCT performance was similar except in NMO eyes where macular thickness parameters were more efficient at detecting abnormalities. A significant correlation was found between N95 amplitude values and OCT-measured macular ganglion cell layer thickness, total retinal thickness, and temporal peripapillary RNFL thickness. PERG amplitude was also significantly associated with VF sensitivity loss. No statistically significant difference was observed with regard to the best-performing parameters of the two methods. CONCLUSIONS: Pattern electroretinogram measurements were able to detect RNFL loss in MS + ON and NMO eyes, with a performance comparable to OCT. PERG amplitude measurements were reasonably well correlated with OCT-measured parameters.

The pupil light reflex in Leber's hereditary optic neuropathy: evidence for preservation of melanopsin-expressing retinal ganglion cells.

PURPOSE: To investigate the pupillary light reflex (PLR) of patients with severe loss of vision due to Leber's Hereditary Optic Neuropathy (LHON) in the context of a proposed preservation of melanopsin-expressing retinal ganglion cells (mRGCs). METHODS: Ten LHON patients (7 males; 51.6 ± 14.1 years), with visual acuities ranging from 20/400 to hand motion perception and severe visual field losses, were tested and compared with 16 healthy subjects (7 males; 42.15 ± 15.4 years) tested as controls. PLR was measured with an eye tracker and the stimuli were controlled with a Ganzfeld system. Pupil responses were measured monocularly, to 1 second of blue (470 nm) and red (640 nm) flashes with 1, 10, 100, and 250 cd/m² luminances. The normalized amplitude of peak of the transient PLR and the amplitude of the sustained PLR at 6 seconds after the flash offset were measured. In addition, optical coherence topography (OCT) scans of the peripapillary retinal nerve fiber layer were obtained. RESULTS: The patient's peak PLR responses were on average 15% smaller than controls (P < 0.05), but 5 out of 10 patients had amplitudes within the range of controls. The patients' sustained PLRs were comparable with controls at lower flash intensities, but on average, 27% smaller to the 250 cd/m² blue light, although there was considerable overlap with the PLR amplitudes of control. All patients had severe visual field losses and the retinal nerve fiber layer thickness was reduced to a minimum around the optic disc in 8 of the 10 patients. CONCLUSIONS: The PLR is maintained overall in LHON patients despite the severity of optic atrophy. These results are consistent with previous evidence of selective preservation of mRGCs.

Evaluation of inner retinal layers in patients with multiple sclerosis or neuromyelitis optica using optical coherence tomography.

PURPOSE: To evaluate the thickness of the inner retinal layers in the macula using frequency-domain optical coherence tomography (fd-OCT) in patients with demyelinating diseases. DESIGN: Cross-sectional study. PARTICIPANTS: A total of 301 eyes of 176 subjects were evaluated. Subjects were divided in 5 different groups: controls, neuromyelitis optica (NMO), longitudinally extensive transverse myelitis (LETM), multiple sclerosis with a history of optic neuritis (MS-ON), and multiple sclerosis without a history of optic neuritis (MS non-ON). METHODS: The individual layers from macular fd-OCT cube scans were segmented with an automated algorithm and then manually hand-corrected. For each scan, we determined the thickness of the retinal nerve fiber layer (RNFL), the combined retinal ganglion cell and inner plexiform layers (RGCL+), and the inner nuclear layer (INL). MAIN OUTCOME MEASURES: Macular RNFL, RGCL+, and INL thickness. RESULTS: The RNFL was significantly thinner than in controls for all patient groups (P ≤ 0.01). Macular RGCL+ thickness was significantly thinner than in controls for the NMO, MS-ON, and MS non-ON groups (P<0.001 for the 3 groups). The INL thickness was significantly thicker than in controls for the patients with NMO (P = 0.003) and LETM (P = 0.006) but not for those with MS-ON or MS non-ON. Although the RNFL and RGCL+ were not significantly different between the NMO and MS-ON groups, the patients with NMO had a significantly thicker INL than the patients with MS-ON (P = 0.02). CONCLUSIONS: Macular RNFL and RGCL+ demonstrate axonal and neural loss in patients with MS, either with or without ON, and in patients with NMO. In addition, the INL thickening occurs in patients with NMO and patients with LETM, and study of this layer may hold promise for differentiating between NMO and MS.