Abstract
PurposeTo present a novel non-parametric algorithm for detecting the position of the human eye limbus in three dimensions and a new dynamic method for measuring the full 360° visible iris boundary known as white-to-white distance along the eye horizontal line.MethodsThe study included 88 participants aged 23 to 65 years (37.7±9.7), 47 females and 41 males. Clinical characteristics, height data and the apex coordinates and 1024×1280 pixel digital images of the eyes were taken by an Eye Surface Profiler and processed by custom-built MATLAB codes. A dynamic light intensity frequency based white-to-white detection process and a novel three-dimensional method for limbus detection is presented.ResultsEvidence of significant differences (p<0.001) between nasal-temporal and superior-inferior white-to-white distances in both right and left eyes were found (nasal-temporal direction; 11.74±0.42 mm in right eyes and 11.82±0.47 mm in left eyes & superior-inferior direction; 11.52±0.45 mm in right eyes and 11.55±0.46 mm in left eyes). Average limbus nasal-temporal diameters were 13.64±0.55 mm for right eyes, and 13.74±0.40 mm for left eyes, however the superior-inferior diameters were 13.65±0.54 mm, 13.75±0.38 mm for right and left eyes, respectively. No significant difference in limbus contours has been observed either between the nasal-temporal direction (p = 0.91) and the superior-inferior direction (p = 0.83) or between the right (p = 0.18) and left eyes (p = 0.16). Evidence of tilt towards the nasal-temporal side in the three-dimensional shape of the limbus was found. The right eyes mean limbus contour tilt around the X-axis was -0.3±1.35° however, their mean limbus contour tilt around the Y-axis was 1.76±0.9°. Likewise, the left eyes mean limbus contour tilt around the X-axis was 0.77±1.25° and the mean limbus contour tilt around the Y-axis was -1.54±0.89°.ConclusionsThe white-to-white distance in the human eye is significantly larger in the nasal-temporal direction than in the superior-inferior direction. The human limbus diameter was found not to vary significantly in these directions. The 3D measures show that the limbus contour does not lay in one plane and tends to be higher on the nasal-inferior side of the eye.
Highlights
The human eyeball casing consists of two connected components; the cornea and the sclera
The white-to-white distance in the human eye is significantly larger in the nasal-temporal direction than in the superior-inferior direction
The 3D measures show that the limbus contour does not lay in one plane and tends to be higher on the nasal-inferior side of the eye
Summary
The human eyeball casing consists of two connected components; the cornea and the sclera. The sclera efficiently handles the forces applied by the extraocular muscles during eye movement without distorting the corneal surface. The limbus is commonly known as the edge of the cornea where it joins the sclera, it may be defined in different ways according to its identification method. With regards to the eye surface profile, the limbus is defined as a smooth transition zone with a more obtuse curvature from the cornea to the sclera [6]. Because it is relatively close to the transparent zone of the cornea, the limbus border is frequently approximated to the visible iris boundary. The iris lies in a different plane a few millimetres away from the limbus plane with no direct contact between them apart from the connection through the ciliary muscles
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