The document describes the optical properties of the human eye. It compares the eye to a camera and describes the key optical elements like the cornea, lens, iris, and retina. It discusses the compound optical system of the eye and provides data on refractive indices and radii of curvature from Gullstrand's schematic eye model. It also describes reduced eye models proposed by Listing and Donders that simplify the eye's optics using single refractive surfaces and focal points.

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