Anomalous relation between axial length and retinal thickness in amblyopic children.

PURPOSE: To investigate the relationship between retinal thickness and axial length in amblyopic eyes compared to healthy eyes. METHODS: In this observational, transversal study, 36 amblyopic children and 30 healthy controls underwent full ophthalmological and orthoptic examinations, volume scanning of the macula with spectral domain optical coherence tomography (3D OCT-1000; Topcon Corporation, Tokyo, Japan), and measuring of axial length using the IOLMaster (Carl Zeiss Meditec AG, Jena, Germany). The average pericentral retinal thickness was calculated. RESULTS: A strong correlation was observed between the axial lengths of both eyes in the control group (R = 0.98, P < 0.01) and between the axial lengths of the amblyopic and fellow eye in the amblyopic group (R = 0.77, P < 0.01); the amblyopic and their fellow eyes were significantly shorter than the nonamblyopic control eyes. The pericentral retinal thickness of both eyes of an individual is highly correlated in nonamblyopic controls (R = 0.92, P < 0.01) and in amblyopic children (R = 0.82, P < 0.01). There is no significant difference in mean pericentral retinal thickness between healthy, amblyopic, and fellow eyes. In healthy eyes a moderate inverse correlation exists between axial length and pericentral retinal thickness (R = -0.41, P = 0.02); this relationship was not found in the amblyopic eyes or the normal fellow eye. CONCLUSIONS: In this patient cohort, there was an anomalous relation between the axial length and the pericentral retinal thickness in both amblyopic and their fellow eyes.

Comparison of retinal nerve fiber layer thickness measurements by spectral-domain optical coherence tomography systems using a phantom eye model.

To quantify differences in nerve fiber layer thickness measurements by various spectral-domain optical coherence tomography (SD-OCT) systems, we developed a phantom eye model. We tested twelve SD-OCT systems of four manufacturers. All systems combined overestimated the 49 µm thick phantom RNFL thickness on average by 18 µm. Within brands, thickness measurements differed statistically significant for one Topcon, one RTVue and one Cirrus. Between brands, thickness determined with RTVue and Topcon differed statistically significant from Cirrus and Spectralis. The maximum difference between mean thicknesses is 3.6 µm within brands and 7.7 µm between brands.

Heartbeat-induced axial motion artifacts in optical coherence tomography measurements of the retina.

PURPOSE: To investigate the cause of axial eye motion artifacts that occur in optical coherence tomography (OCT) imaging of the retina. Understanding the cause of these motions can lead to improved OCT image quality and therefore better diagnoses. METHODS: Twenty-seven measurements were performed on 5 subjects. Spectral domain OCT images at the macula were collected over periods up to 30 seconds. The axial shift of every average A-scan was calculated with respect to the previous average A-scan by calculating the cross-correlation. The frequency spectrum of the calculated shifts versus time was determined. The heart rate was determined from blood pressure measurements at the finger using an optical blood pressure detector. The fundamental frequency and higher order harmonics of the axial OCT shift were compared with the frequency spectrum of blood pressure data. In addition, simultaneous registration of the movement of the cornea and the retina was performed with a dual reference arm OCT setup, and movements of the head were also analyzed. RESULTS: A correlation of 0.90 was found between the fundamental frequency in the axial OCT shift and the heart rate. Cornea and retina move simultaneously in the axial direction. The entire head moves with the same amplitude as the retina. CONCLUSIONS: Axial motion artifacts during OCT volume scanning of the retina are caused by movements of the whole head induced by the heartbeat.

Optical phantoms of varying geometry based on thin building blocks with controlled optical properties.

Current innovations in optical imaging, measurement techniques, and data analysis algorithms express the need for reliable testing and comparison methods. We present the design and characterization of silicone elastomer-based optical phantoms. Absorption is included by adding a green dye and scattering by adding TiO(2) or SiO(2) particles. Optical coherence tomography measurements demonstrate a linear dependence of the attenuation coefficient with scatterer concentration in the absence of absorbers. Optical transmission spectroscopy of the nonscattering absorbing phantoms shows a linear concentration dependent absorption coefficient. Both types of samples are stable over a period of 6 months. Confocal microscopy of the samples demonstrates a homogeneous distribution of the scatterers, albeit with some clustering. Based on layers with thicknesses as small as 50 mum, we make multifaceted structures resembling flow channels, (wavy) skin-like structures, and a layered and curved phantom resembling the human retina. Finally, we demonstrate the ability to incorporate gold nanoparticles within the phantoms. In conclusion, our phantoms are easy to make, are based on affordable materials, exhibit well-defined and controllable thickness, refractive index, absorption, and scattering coefficients, are homogeneous, and allow the incorporation of novel types of nanoparticle contrast agents. We believe our phantoms fulfill many of the requirements for an "ideal" tissue phantom, and will be particularly suited for novel optical coherence tomography applications.