This PPT contains: The schematic and Reduced eye The Axes and Angle of the eye

1. The Schematic and
Reduced Eye
Ms. Khushi Kansal
Assistant Professor
Subharti Medical College (Department of Paramedical Sciences)
Swami Vivekanand Subharti University

2. Schematic
Eye
 A schematic eye is a mathematical and physical modal
that represents the basic optical features of the real eye.
 Objectives:- To provide a basis for the theoretical studies
of the eye as an optical instrument, teaching aids in
optics, optometry, ophthalmology, vision, and visual
perception.
 History:- Listing and Gauss while studying refraction by
lens combination, concluded that for a homocentric
lenses system there exist three pairs of cardinal points
 1. two principal foci
 2. two principal points
 3. two nodal points

3. According to
the Gullstrand
model:
 Cardinal data:-
 Principal foci F1 and F2 lie 15.7 mm in front and 24.4
mm behind the cornea.
 Principal points P1 and P2 lie in the anterior chamber
1.35 mm and 1.60 mm behind the anterior surface of
the cornea.
 Nodal points N1 and N2 lie in the posterior part of the
lens 7.08 mm and 7.33 mm behind the anterior
surface of the cornea.
 The total dioptric power of this schematic eye is 58.64D.
Refractive indices:-
Cornea 1.376
Aqueous 1.336
Lens cortex 1.386
Lens Core 1.406
Vitreous 1.336

4.  Radius of curvature of the refractive
surface
 Anterior surface of the cornea 7.70 mm
 Posterior surface of cornea 6.70mm
 Anterior surface of the lens 10.00mm
 Posterior surface of the lens 6.00mm
 Anterior surface of lens core 7.91mm
 Posterior surface of the lens core 5.76mm

5. The Reduced
Eye
 The reduced eye is an idealized Model of the optics
of the human eye. Listing and Donders have
simplified the reduced eye.
 Listing’s Reduced Eye: A single principal point
and a single nodal point lying midway between two
principal points and two nodal points respectively is
called Listing’s reduced eye.

6. Listing’s
Reduced Eye
 Data of Listing’s reduced eye :
 Principle Point (P) lies 1.5 mm behind the anterior
surface of cornea.
 Nodal point (N) is situated 7.2 mm behind the
anterior surface of cornea.
 Anterior focal point (F¹) is 15.7 mm in front of the
anterior surface of the cornea.
 Posterior focal point (F2) s 24.4 mm behind the
anterior surface of the cornea.
 Anterior focal length (f¹) is 17.2 mm (15.7 +1.5)
 Posterior focal point(F2) is 22.9 mm (24.4- 1.5)
 Total dioptric power of the reduced eye is about +60
D ( +43D is cornea and +17D crystalline lens).

7. Donder’s
Reduced Eye
 Donders’ Reduced Eye: The optical system of the
eye is treated as a single article reflecting surface.
This is called Donders’ reduced eye.
 Data of Donders’ reduced eye:
 Principle point lies 2 mm behind the corner with a
radius of curvature of 5mm
 Nodal point is situated 5mm behind the plane.
 Anterior focal(f1) length is a 15 mm •Posterior focal
(f2) length is 20mm Refractive index is 1.336
 Total power is +60D

8. Significance of
the Reduced
Eye:
 Designing the instrument
 Making calculation
 Localizing a foreign body
 Derived formula for the intraocular lens power

10. Axes of the
Eye
1. Optical axis: is the line passing through
the centre of the cornea (P) and the centre of
the lens (N) and meets the retina (R) on the
nasal side of the fovea.
2. Visual axis: is the line joining the fixation
point (O), nodal point (N) and the fovea (F).
3. Fixation axis: is the line joining the
fixation point (O) and the centre of rotation
(C).

11. VisualAngles
1. Angle alpha: It is the angle (ONA) formed
between the optical axis (AR) and visual axis (OF)
at the nodal point (N).
2. Angle gamma: it is the angle (OCA) between the
optical axis (AR) and the fixation axis (OC) at the
centre of rotation of the eyeball (C).
3. Angle kappa: It is the angle (OPA) formed
between the visual axis (OF) and the pupillary line
(AP). The point P on the centre of the cornea is
considered equivalent to the centre of pupil.