Schematic & Reduced Eye.pptx

I am Bagbul Seikh. Department of optometry 3rd sem .Swami Vivekanand university.

1. Visual optics introduction Eye as an optical instrument : The Eye can be compared with a camera – Eyelids - shutter of the camera Cornea & Crystalline lens - focusing system of the camera Iris acts a diaphragm - regulates the size of the aperture (pupil) and therefore the amount of light entering the eye Choroid – formed the darkened interior of the camera Retina – light sensitive plate or film (on which image is formed)

2. Compound optical system of eye A) Corneal portion - Include tear layer (separates air from aqueous humour ) B) Lens portion - Separates aqueous humour from vitreous humour Focusing system: cornea, aqueous humour , crystalline lens & vitreous humour Total dioptric power of eye- +58D - +60D Corneal dioptric power- +43D Crystalline lens power- +15D - +17D

3. Schematic Eye Cardinal Data of the Gullstrand’s schematic eye Principal foci F1 & F2 lie 15.7 mm in front of and 24.4 mm behind the cornea Principal points P1 & P2 lie in the anterior chamber 1.35mm and 1.60 mm behind the anterior surface or cornea Nodal points N1 & N2 lie in the posterior part of lens 7.08mm and 7.33 mm behind the anterior surface of cornea

4. Gullstrand’s data on refractive indices of the components of the optical system of eye are : Cornea- 1.376 Aqueous- 1.336 Lens cortex- 1.386 Lens core- 1.406 Vitreous- 1.336 Gullstrand’s data of radii of curvature of the refractive surfaces are : Anterior surface of cornea – 7.70 mm Posterior surface of cornea – 6.70 mm Anterior surface of lens cortex – 10.00 mm Anterior surface of lens core – 7.91 mm Posterior surface of lens core – 5.76 mm Posterior surface of lens cortex – 6.00 mm

5. Position of optical elements in the eye: Anterior surface of cornea – 0 mm Posterior surface of cornea – 0.5 mm Anterior surface of lens – 3.6 mm Posterior surface of lens – 7.2 mm Refracting power data included in Gullstrand’s schematic eye: Optical System Power (in D) Accommodation relaxed Power (in D) Accommodation maximum Complete optical system of the eye 58.64 70.57 Corneal system 43.05 43.05 Lens system 19.11 33.06

6. Reduced Eye Listing’s Reduced Eye For understanding, Listing simplified the data by choosing single principal point and single nodal point lying midway between two principal points and two nodal points respectively – this is called Listing’s reduced eye. Principal point P lies 1.5 mm behind the anterior surface of cornea and represents the vertex of a single refracting surface whose radius of curvature is 5.7 mm Nodal point N is situated 7.2 mm behind the anterior surface of cornea [at the centre of curvature of single refracting surface (1.5+5.7 =7.2 )] Anterior focal point is 15.7 mm in front of the anterior surface of cornea

7. Posterior focal point (on the retina) is 24.4 mm behind the anterior surface of cornea Anterior focal length is 17.2 mm (15.7 + 1.5) posterior focal length is 22.9 mm (24.4 - 1.5 ) Uniform refractive index – 1.336 Total dioptric power +58.20 [Refractive power = Refractive index / Focal length (in metres )]

8. Donders ’ Reduced eye Converted the cardinal data into round figures In his over simplified reduced eye, eye as a single curved surface The plane of the curved surface is 2 mm behind the cornea with a radius of curvature of 5mm Nodal point is situated 5 mm behind the plane Anterior focal length is 15 mm Posterior focal length is 20 mm Refractive index is 1.336 Total power is +60 D