Reduced eye

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

1. RAY , ARBIND OPTOMETRIST, SCEh 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.

3. 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

4. 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

5. 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

6. 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

7. 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.

8. 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

9. 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

10. 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

11. 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

12. 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.

13. Q u e stions

14. THANK YOU