reduced eye power point presentation for optometry student . actual examination & theory of reduced eye etc.

1. RAY,ARBIND
O P TO M E T R I S T, S C E H
PRINCIPLE OF SCHEMATIC
EYE AND DIFFERENT
PARAMATERS OF IT

2. Schematic eye
 A schematic eye is a mathematical or physical model
that represents the basic optical features of the real
eye
 It provide a basis concept for theoretical studies of
the eye as an optical instrument.

4. Parameters of schematic eye
 Focal ponts F1 and F2 lie 15.7mm infront of and
24.4mm behind the cornea.
 Principal points P1 and P2 lie in the anterior chamber
1.35mm and 1.60mm behind the anterior surface of
cornea.
 Nodalpoints N1 and N2 lie in the posterior part of lens
7.08mm and 7.33mm behind the anterior surface of
cornea.
 Refracting power of complete optical system of the
gullstrand’s schematic eye is 58.64D

5. Cont..
 Gullstrand’s data on refractive indices of the
components of the optical system of eye are as
below;
Cornea 1.376
Aqueous 1.336
Lens cortex 1.386
Lens core 1.406
Vitreous 1.336

6. Cont..
 Gulstrand’s data for radii of curvature of the
refractive surfaces are as below;
Ant. surface of cornea 7.70m
Post.surface of cornea 6.70mm
Ant.surface of lens cortex 10.00mm
Post. surface of lens cortex 6.00m
Ant. surface of lens core 7.91mm
Post. surface of lens core 5.76mm

7. Cont…
 Position of optical elements in the eye is;
Ant. surface of cornea 0mm
Post . surface of cornea 0.5mm
Ant. Surface of lens 3.6mm
Post. Surface of lens 7.2mm

8. The Reduced Eye
 For better understanding of the optics of
eye,therefore for understanding,listing simplifed the
data by choosing single principal point and single
nodalpoint lying midway between two focal
point.this is called listing’s reduced eye.

10. Parameter of Listing’s reduced eye
 Principal point lies 1.5mm behind the anterior
surface of cornea.
 Nodal point is situated 7.2mm behind the anterior
surface of cornea.
 Anterior focal point is 15.7mm in front the anterior
surface of cornea.
 Posterior focal point is 24.4mm behind the anterior
surface of cornea.
 Uniform refractive index is 1.336
 Total dioptric power is +58.20D

11. The refractive power of the reduced eye is calculated
by dividing refractive index by focal length.
 Using the anterior focal length,the power of the eye is
calculated as;
Refractive index of air
F= Anterior focal length in metres
i.e F= 1x100 =58.20D
17.2

12.  Using the posterior focal length,the power of the eye
is calculated as;
F= Refractive index of vitreous
posterior focal length in metres
i.e F= 1.33x1000
22.9 =58.20D

13. Donder’s reduced eye
 Donders converted the cardinal data into round figures,so that they can
be remembered easily.
 In his oversimplified reduced eye,he treated the eye as a single curved
surface with following cardinal data;
 The plane of the curved surface is 2mm behind the cornea with a
radius of curvature of 5mm
 Nodal point is situated 5mm behind the plane
 Anterior focal length is 15mm
 Posterior focal length is 20mm
 Overall Refractive index is 1.336
 Total power is 60D

14. SCHEMATIC VS REAL EYE
 Schematic eye models are approximations to real eyes
 use only spherical surfaces and
 lenses of constant refractive index,
 known as paraxial models.
 Real eyes have aspheric surfaces and a lens with a gradient index.
 Accuracy of schematic eyes can be improved by
 Aspherising one or more spherical surfaces or
 using a gradient refractive index lens or
 both.
 are called ‘finite aperture’ or ‘wide angle’ schematic eyes.

15. Questions

16. THANK YOU