Eyeball Images Download
MUNEHARU KAMADA
These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.
Your eyes also need tears to work correctly.
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As we go past eyelids, the next component is the circular frontage of the spherical eyeball, termed as cornea. Cornea is the first optical component of the eye machinery, dealing first-hand with the incoming light. Its function is of a primary filter, before passing on the light to the lens and retina.
The central portion of the front of the eyeball is termed as iris. Iris is a pigmented structure. Eye color (black, brown, blue etc.) is defined by the pigmentation of iris. The central aperture of iris is called pupil.
Located right behind the pupil is the transparent structure termed as the lens, responsible for correct focusing of the visuals. It is flexible in nature, and adjusts according to the external lighting. The lens is encapsulated in a thin transparent body, and is connected with the eyeball by a pair of muscles. It refracts the light, and helps in focusing it correctly to the back of the eyeball (retina).
Retina is the innermost layer of the eyeball structure. Retinal membrane can be imagined as the wall on which the images are projected. The light passing through cornea, pupil, and lens gets focused on the retinal membrane. In addition to tissue components, retina is made up of two types of cells: rod cells and cone cells. The former are considered to be responsible for dim light vision, whereas the latter are considered to be responsible for bright light vision. Cones play a critical role in perception of the images with sharp contrast. Deficiency of either type of cells would cause abnormalities in the ocular function.
Choroid is the middle layer of the eyeball wall, sandwiched between retina and sclera. It also helps in clarity of vision by absorbing excess light. The muscles which attach sclera to the iris are termed as ciliary body, which play a role in flexible focusing of the image through the lens.
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A surgical simulator with elaborate artificial eyeball models has been developed for ophthalmic surgeries, in which sophisticated skills are required. To create the elaborate eyeball models with microstructures included in an eyeball, a database of eyeball models should be compiled by segmenting eye structures based on high-resolution medical images. Therefore, this paper presents an automated segmentation of eye structures from micro-CT images by using Fully Convolutional Networks (FCNs). In particular, we aim to construct a method for accurately segmenting eye structures from sparse annotation data. This method performs end-to-end segmentation of eye structures, including a workflow from training the FCN based on sparse annotation to obtaining the segmentation of the entire eyeball. We use the FCN trained on the slices sparsely annotated in a micro-CT volume to segment the remaining slices in the same volume. To achieve accurate segmentation from less annotated images, the multi-class segmentation is performed by using the network trained on the preprocessed and augmented micro-CT images; in the preprocessing, we apply filters for removing ring artifacts and random noises to the images, while in the data augmentation process, rotation and elastic deformation operations are performed on the sparsely-annotated training data. From the results of experiments for evaluating segmentation performances based on sparse annotation, we found that the FCN trained with data augmentation could achieve high segmentation accuracy of more than 90% even from a sparse training subset of only 2.5% of all slices.
"Floaters" and flashes are a common sight for many people. Floater is a catchall term for the specks, threads, or cobweb-like images that occasionally drift across the line of vision. Flashes are sparks or strands of light that flicker across the visual field. Both are usually harmless. But they can be a warning sign of trouble in the eye, especially when they suddenly appear or become more plentiful.
A floater is a tiny cluster of cells or fleck of protein lodged in the vitreous humor. This clear, stable gel, which looks like raw egg white, supports and fills the rear two-thirds of the eyeball (see "The inside story"). The vitreous provides a pathway for light coming into the eye through the lens. The vitreous connects to the retina, the patch of light-sensitive cells along the back of the eye that captures images and sends them to the brain via the optic nerve.
Methods: In this prospective observational study participants underwent orbital MRI during central, right, left, up, and down gazing. MRI scans were processed using self-developed software; this software enabled 3D MR image reconstruction and the superimposition of reconstructed image sets between different gazes. After acquiring the coordinates of the eyeball centroid in each gaze, the changes in centroid coordinates from central gaze to the other gazes were estimated, and correlations with associated factors were evaluated.
Technical advancements in magnetic resonance imaging (MRI) now enable the in-depth and non-invasive study of eye movement in living subjects (9, 10). MRI provides high soft tissue contrast along with high spatial resolution in multiple planes (11), enabling the anatomical structure of the orbit to be visualized in detail. Therefore, MRI has contributed to the investigation of functional eyeball position and the determination of the effect of EOMs during gaze shifts (12). Moreover, the digital reconstruction of MRI images enables the analysis of complex 3D eye movements during visual gaze (13).
Schematic figure of the MR images acquisition setup (A) in a axial view and (B) in a sagittal view. Small blue circles indicate the fixation targets. Fixation targets are on the inside of the scanner bore and the bore diameter is 60 cm. Fixation targets are placed at a 30 angle of the gaze when assessing horizontal movements and a 20 angle of the gaze when assessing vertical movements.
Quantitative measurement of the movement of the eyeball centroid. For the primary position (central gaze), the extracted outline of the eyeball image is marked with a yellow line and the centroid of the eyeball is marked with a yellow dot. In horizontal gaze, the eyeball outline is marked with a pink line and a red dot indicates the centroid of the eyeball. The centroid, which is the geometrical center of the extracted eyeball, was automatically obtained in the form of x, y, and z coordinates. In the superimposed image, which was adjusted using static tissues, the distance of centroid movement was obtained using the distance formula, and the direction of centroid movement was calculated with the arctangent formula. The blue arrow indicates the movement of the centroid.
Schematic figure showing the values used in image analysis. To evaluate the positional change of the eyeball, we measured the distance (d) and direction (θ) of eyeball centroid movement between the primary position (black dot) and each secondary position (white dot). In horizontal gaze, axial plane (X-Y plane) images were used and the appropriate x and y coordinates were calculated to determine the distance and direction of eyeball translation. In vertical gaze, sagittal plane (Y-Z plane) images were used, and y and z coordinates were calculated. The red arrow indicates centroid movement.
Schematic figures to represent the mean distance and direction of centroid movement in horizontal eye movements. The mean distance of centroid movement was 0.69 0.27 mm in abduction and 0.68 0.27 mm in adduction. The eyeball moved in the direction of the gaze during horizontal gaze.
Superimposed MR images showing the translatory movements of the eyeball. The yellow and red dots indicate the centroid of the eyeball in the primary and secondary positions, respectively. The blue arrow indicates the movement of the centroid of each eyeball. Eyeballs move toward the gaze direction in the axial plane during horizontal gaze. (A) When the subject looks to the right, the centroids of both eyeballs translate to the right. (B) Similarly, when the subject looks to the left, the centroids of both eyeballs translate to the left. The translatory movement of the eyeball in the sagittal plane is in the opposite direction to the gaze during vertical gaze. (C) The eyeball is translated downwards when looking upwards, and (D) translated upwards when looking downwards.
The eye is suspended in the orbit surrounded by soft fat pads; this allows it to translate to some extent, as one can verify by pushing on the eye through the eyelid (3). However, most studies of eye movement have only examined rotational movements about a fixed center of rotation. Previous studies have reported that the eyeball can be well-approximated as a spherical joint with its center fixed in the head, such that only rotations around three orthogonal axes passing through the center of the eye need to be considered (7). Von Noorden also concluded that translatory movements may be disregarded from a practical standpoint (5). Unfortunately, despite acknowledging the occurrence of eyeball translation, they assumed that it is a negligible part of eye movement; thus, most researchers have studied only the rotational components of the entire eye movement pattern. The advantage of this assumption is that it is easier to approach eye movement and to apply basic physiological laws of motion to the complex ocular kinematics. However, our results show that the eyeball not only rotates, but also changes in position. We demonstrated a significant change in the coordinates of the centroid of the eyeball in all gaze directions. These findings suggest that the movement of the eye, like other rigid bodies, is dictated by the basic kinetics of rotational and translatory movement.
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