The document discusses various optical aberrations of the normal eye that cause imperfect focusing of light onto the retina. It describes lower order aberrations like myopia, hyperopia and astigmatism as well as higher order aberrations involving issues like blurred vision. Specific aberrations covered include chromatic aberration due to different focal lengths for different wavelengths of light, spherical aberration due to peripheral rays focusing at different points than paraxial rays, coma affecting point sources of light, and oblique aberration influencing image quality through spherical lenses. While the eye possesses these aberrations, their effects are generally negligible for functional vision due to compensating factors in the eye.

1. OPTICAL ABERRATIONS OF THE
NORMAL EYE
Presented by :
ANUSKA CHAKRABORTY
23401721014
Visual Optics
234-NSHM COLLEGE OF MANAGEMENT
& TECHNOLOGY, KOLKATA

2. Optical Aberrations are the Imperfections of the Eye
that light is unable to Focus onto the Retina effectively
• Refractive errors (myopia, hyperopia and astigmatism) are the
most common ocular aberrations
• Lower Order Aberrations – Myopia, Hypermetropia & Astigmatism
• Higher Order Aberrations – Diplopia, Contrast Issues, Glare, Limited
Night Vision, Blurred Vision
• Chromatic Aberration – Defects due to White light
• Monochromatic Aberration – Defects due to Monochromatic Lights

3. Diffraction of Light
• Bending of Light
caused by the rim of a
Lens or Light falls at
peripheral border of
Pupil
• Airy Disc : Light brought
to a focus doesn’t come
to a point,creates
blurred disc of light
surrounded by several
Bright & Dark bands
• Inversely
proportionate with

4. Spherical Aberrations
• Incoming Light
rays are not
focusing in a
single point
• Spherical lens
refracts
Peripheral rays
more strongly
than Paraxial rays
• Directly
proportionate
with Pupil size

5. Chromatic Aberrations
• A failure of lens to focus
all colors to the same
point
• Eye is Myopic for Violet &
Hypermetropic for Red
Lights
• Achromatic Lens is
designed to bring two
wavelengths into focus on
a same plane(retina)
• Directly proportionate
with the Refractive
index of the Lens

6. Decentring
• The surfaces of
Cornea & Lens are
not centered on a
common (visual)
axis
• Report: Cornea’s
centre of curvature
is situated about
0.25mm below the
axis of the lens

7. Oblique Aberration
• Influences the image
quality of spherical
lenses
• When a wearer looks
at an angle through
the lens, there is a
deviation occurs
which he perceives as
blur
• Directly
proportionate with
the Dioptric power of
Lens

8. Coma
• Dominant
aberration of
human eye
• Due to the
different areas of
Lens light focuses
different points on
retina
• Produces in the
image plane a
‘Coma Effect’ from
a point source of

9. Eyes are not optically perfect. Fortunately, the eye
possess those imperfections to so small a degree that, for
functional purposes, their presence are negligible.
• Cutting off peripheral rays by iris
• High refractive index of core of nucleus of lens than peripheral
cortex
• Low sensitivity of peripheral retina
• Stiles – Crawford effect, more sensitivity of retina for perpendicular
rays than oblique rays

10. References: ‘OPTICS & REFRACTION’ by AK KHURANA and images credit Google