M2 Dioptrics Of The Eye Flashcards
Light travels through any even transparent body, such as the atmosphere, in a straight line. But when it meets any change in density, particularly when it has to pass obliquely into a denser medium, the ray is bent so as to run in a direction more perpendicular to the surface of the denser body.
The degree of bending or refraction of the rays depends on the difference in optical density of the two media and the angle at which the ray strikes the surface of the more dense.
Dioptrics of the eye
Components of Dioptrics
Curvature
Thickness
Axial length
Refractive index
Cardinal points of the eye
2 Principal Points
2 Focal Points
2 Nodal Points
point of intersection of the principal plane with the optical axis.
P1 - first principal point
P2 - second principal point
Principal points
points at which light rays arrive parallel to the optic axis are brought to a common focus on the optical axis.
the focus of parallel rays of light after refraction by a lens or reflection by a curve mirror.
F1 - first principal focus (object space)
F2 - second principal focus (image space)
Focal points
emerge from the 2nd nodal point parallel to it’s original direction.
points in the lens on the principal axis from which objects and images appear under the same angle or;
a ray directed to a nodal point at the same angle will exit the lens at the same angle.
N1 - front nodal point
N2 - back nodal point
Nodal points
is an imaginary straight line drawn horizontally, passing through the center of rotation & makes right angle with vertical axis.
X AXIS / TRANSVERSE / HORIZONTAL AXIS
an imaginary straight line drawn from the anterior pole of the eye passing through the nodal point, the center of rotation and terminates at posterior pole of the eye.
Z AXIS / AP AXIS
an imaginary straight line drawn vertically, passing through the center of rotation & makes right angle with horizontal axis.
Y AXIS / VERTICAL AXIS
the line joining the object of regard to the center of rotation of the eye.
FIXATION AXIS
the frontal plane found to be tangential to the chin & super ciliary ridges
Face plane
a frontal plane that contains the centers of rotation of both eyes
Listing’s plane
a line that connects the center of rotation of both eyes
Base line
the plane which includes the baseline & object of regard
Plane of regard
a plane that divides the head into right & left halves.
Median plane
