Quantitative Analysis of Fundus-Image Sequences Reveals Phase of Spontaneous Venous Pulsations.

PURPOSE: Spontaneous venous pulsation correlates negatively with elevated intracranial pressure and papilledema, and it relates to glaucoma. Yet, its etiology remains unclear. A key element to elucidate its underlying mechanism is the time at which collapse occurs with respect to the heart cycle, but previous reports are contradictory. We assessed this question in healthy subjects using quantitative measurements of both vein diameters and artery lateral displacements; the latter being used as the marker of the ocular systole time. METHODS: We recorded 5-second fundus sequences with a near-infrared scanning laser ophthalmoscope in 12 young healthy subjects. The image sequences were coregistered, cleaned from microsaccades, and filtered via a principal component analysis to remove nonpulsatile dynamic features. Time courses of arterial lateral displacement and of diameter at sites of spontaneous venous pulsation or proximal to the disk were retrieved from those image sequences and compared. RESULTS: Four subjects displayed both arterial and venous pulsatile waveforms. On those, we observed venous diameter waveforms differing markedly among the subjects, ranging from a waveform matching the typical intraocular pressure waveform to a close replica of the arterial waveform. CONCLUSIONS: The heterogeneity in waveforms and arteriovenous phases suggests that the mechanism governing the venous outflow resistance differs among healthy subjects. TRANSLATIONAL RELEVANCE: Further characterizations are necessary to understand the heterogeneous mechanisms governing the venous outflow resistance as this resistance is altered in glaucoma and is instrumental when monitoring intracranial hypertension based on fundus observations.

Visualization of fundus vessel pulsation using principal component analysis.

PURPOSE: Spontaneous venous pulsation is one of the clinical signs with which to rule out elevated intracranial pressure and papilledema. More subtle pulsatile retinal movements are difficult to observe because of eye movements. Recording a fundus movie and aligning (registering) the images helps, but the images still contain distracting microsaccadic distortions and noise. The authors hypothesized that addressing these latter points should allow observation of minute pulsating features in fundus movies. METHODS: Principal component analysis (PCA), a basic form of blind source analysis, is applied to recorded fundus image sequences. The authors demonstrate this method in 5-second image sequences acquired with a near-infrared SLO (HRA+OCT Spectralis). The images are first registered to correct for eye drift, then microsaccade-distorted images are rejected, and the remaining image sequence is decomposed into principal components. Finally, a movie is constructed using the first five principal components (these had pulsatile features). RESULTS: Each of the processing steps (registration, cleaning, PCA filtering) improves the detection of pulsatile features, ultimately allowing clear visualization of spontaneous venous pulsation. Depending on the subject, additional features can be observed: pulsation amplitude of the arterial tree of approximately 10 µm, pulsation of arterioles down to 70-µm diameter, complete venous collapse, overall optic nerve head tissue pulsation, and mechanical links between veins and arteries. CONCLUSIONS: By disentangling pulsatile motion from other dynamic components of retinal images, unprecedented resolution in physiologic motion of retinal vessel structure is achievable.

Multifocal electroretinographical changes in monkeys with experimental ocular hypertension: a longitudinal study.

PURPOSE: To study the time course of changes in the multifocal electroretinograms (mfERG) in monkeys with experimental ocular hypertension (OHT). METHODS: The mfERGs were recorded in 12 eyes out of 6 monkeys. Two baseline measurements were used to quantify the reproducibility, the inter-ocular and the inter-individual variability of the ERG signals. Thereafter, the trabeculum of one eye of each animal was laser-coagulated in one to three sessions to induce OHT. ERG measurements were repeated regularly in a period of 18 months and the changes in ERG waveforms were quantified. RESULTS: All animals displayed OHT (between 20 and 50 mmHg) in the laser-coagulated eyes. An ERG change was defined as the sum of differences during the first 90 ms between the laser-coagulated eye and the same eye before laser coagulation and between the laser-coagulated eye and the non-treated fellow eye. Three animals displayed significant changes for nearly all retinal areas and all stimulus conditions. The three remaining animals displayed significant changes only in one comparison, indicating very mild changes. The data indicate that a high stimulus contrast is more sensitive to detect changes, probably because of a better signal-to-noise ratio. Moreover, the comparisons with the fellow eye are more sensitive to detect changes than comparisons with the measurements before laser-coagulation. CONCLUSIONS: OHT does not always lead to ERG changes. Comparisons with fellow eyes using high contrast stimuli are more sensitive to detect changes related to OHT.