What is optical and lens aberration? What are the types of the aberration and how to treat and correct them?

1. Aberration
By: Asmaa J. Abdalwahid
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2. • Aberration occurs when the incident light fails to focus at a single
point.
• The aberration types are:
1. Monochromatic aberrations (can be produced with a single wavelength of
light):
• Spherical Aberration
• Coma
• Oblique Astigmatism
• Power Error (Field Curvature)
• Distortion
2. Chromatic aberration (occur only with polychromatic light).
Aberration
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3. Monochromatic aberrations
• They called monochromatic aberrations, since they occur
independently of color.
• The 5 Seidel aberrations are spherical aberration, coma, oblique
astigmatism, curvature of field (power error), and distortion.
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* Peripheral rays are those that enter the lens nearer the edge
of the lens.
* Paraxial rays are those that pass through the central area of
the lens.
Peripheral rays

4. Monochromatic aberrations
Aberration orders:
According to the orders of aberrations,
2nd order aberrations are errors which
are corrected by the written ophthalmic
eyeglass prescription using sphere and
cylinder lenses.
Those aberrations classified as 3rd order
and up are referred to as higher order
aberrations
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Order Aberration
1st Prism
Low
order
2nd Defocus (spherical refractive
error) and astigmatism
3rd Coma and trefoil
High
order
4th Spherical aberration
5th – 10th
Higher order irregular
aberrations (not present in
spherical surfaces)

5. Monochromatic aberrations
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1. Spherical aberration
Occurs when the incoming light rays focus at
different points when they pass through a spherical
surface.
Peripheral rays refract more than the paraxial rays,
so they will focus at different Points.
It can be reduced by reducing pupil size, and correct
by aspherical lens.
Spherical aberration
Aspherical lens

6. Monochromatic aberrations
2. Coma
It results when the light rays are oblique with respect to the optical axis.
A point image is blurred into a comet shape when rays from an off-axis object
point are imaged by different zones of the lens.
It causes a high image asymmetry and deformity.
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7. Monochromatic aberrations
2. Coma
When the tip of the comet is pointed toward the optical axis, the coma is said
to be positive, and when it is pointed away, the coma is negative.
As spherical aberration, coma can be minimized by smaller pupil size, and by
aspherical lens.
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8. Monochromatic aberrations
3. Oblique Astigmatism
When a small bundle of light strikes the
spherical surface of a lens from an
angle, oblique astigmatism causes the
light to focus as two line images,
known as the tangential and sagittal
images, instead of a single point.
If we focus the sensor for the sagittal
plane, we see circles become ellipses in
the tangential direction and vice versa.
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9. Monochromatic aberrations
4. Field Curvature
Field curvature aberration describes the fact that parallel rays reaching the
lens from different directions do not focus on a plane, but rather on a curved
surface. The image plane for a flat object is curved, resulting in curvature of
field.
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10. Monochromatic aberrations
5. Distortion
Geometrical deformation of an image.
It occurs because there is a different
magnification at different areas of the periphery
of the lens in proportion to the distance of those
areas from the OC of
the lens.
- Barrel distortion: occurs because
minification in the periphery of a minus lens
is greater than in its center.
- Pincushion distortion: results from greater
magnification in the periphery of a plus lens
compared to its center.
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Barrel
(occurs in negative lens)
Pincushion
(occurs in positive lens)

11. Chromatic Aberration
Transverse (Lateral) Longitudinal (Axial)
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The failure of a lens to focus all colours in the same plane is known as chromatic
aberration.

12. Chromatic Aberration- Longitudinal
Longitudinal chromatic aberration occurs when each colour focus on
different point on the optical axis. This is because of the dioptric difference
between the colours.
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13. Chromatic Aberration- Lateral
Lateral chromatic aberration is expressed either as differences in image
magnification or differences in prismatic effect.
1. Magnification Differences: A magnification difference is the difference in size between
the images formed by two different wavelengths, such as red and blue.
2. Differences in Prismatic Effect: When quantified by prismatic effect, the lateral
chromatic aberration of a prism is the difference in prismatic effect for light of two
different wavelengths.
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14. Chromatic Aberration
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The patient is not looking through the optical
centers of the lenses, but above them, this
may result in lateral chromatic aberration
that reduces visual acuity.
Chromatic aberration increase with:
- High powered lens
- High indexed lens
- Low Abbé value
- The more distance from the optical center.

15. Achromatic Lens
• An achromatic lens is constructed
from two different materials, each
with a different refractive index, one
is a plus lens and the other is a minus
lens of another material.
• Achromatic lenses are not used in
normal spectacle lenses.
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16. Peripheral Aberration
• The largest aberrations present when the
object is located on the optical axis are
spherical aberration and longitudinal
chromatic aberration (A in the image) these
aberrations occurs on the optical axis.
• When going to off-axis angles, coma and
transverse chromatic aberration will become
apparent to cause peripheral aberration (B)
• Larger angles will cause more peripheral
aberration such as in oblique astigmatism
aberration (C).
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17. • Ocular aberrations are imperfections of the eye that result in light
being unable to focus onto the retina effectively as well as defects in
visual image.
• There are two types of aberrations in the eye:
1. Lower-order aberrations: the most common causes of vision
problems, they include astigmatism, positive defocus (myopia),
and negative defocus (hyperopia).
2. Higher-order aberrations: are unable to be corrected by cylinder
or spherical corrections, they include spherical aberrations, coma
and trefoil.
Ocular Aberration
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18. 18
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Oculus Aberration

19. • Ocular aberrations are imperfections of the eye that result in light
being unable to focus onto the retina effectively as well as defects in
visual image.
• There are two types of aberrations in the eye:
1. Lower-order aberrations (85%): the most common causes of
vision problems, they include astigmatism, positive defocus
(myopia), and negative defocus (hyperopia).
2. Higher-order aberrations (15%): they include spherical
aberrations, coma and trefoil. They are hard to treat and correct.
Ocular Aberration
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20. 1. Lower-order aberrations:
• Defocus aberration is simply an image out of focus; if the focal
point is in front of target surface (retina) then it is positive defocus,
and it is negative defocus if it is behind the target surface.
Ocular Aberration
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Positive defocus (myopia)
Normal focus
(hyperopia) Negative defocus

21. Ocular Aberration
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2. Higher-order aberrations:
• A higher-order aberration is a distortion acquired by a wavefront of light when it passes
through an eye with irregularities of its refractive media (tear film, cornea, aqueous
humor, crystalline lens and vitreous humor) and approximately 90% are caused by the
problems of the cornea.
• It is less in young people and increase with the age.
• They can also occur as a result of the following:
- Eye diseases such as cataracts
- Abnormal curvature of the cornea and the lens
- Corneal dystrophies
- Corneal scarring after injury, infection or surgery
- Tear film disorders and dry eye
- Refractive Surgery.

22. Ocular Aberration
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Higher-order aberrations is more common in People with larger pupil sizes
particularly in low lighting conditions when the pupil opens even wider.
• The symptoms of higher order aberrations can be varied:
1. double vision sensation and ghost image
2. halos
3. Glare
4. starburst
5. loss of contrast especially at night
6. poor night vision
7. blurred vision
8. lack of clarity
9. blurred edges of letters and poor detail diplopia

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24. 2. Higher-order aberrations:
A. Spherical aberration: This defect prevents peripheral light rays from focusing on
the retina, resulting in blurred and halosed vision, it increase with wide pupil.
B. Trefoil aberration: Is a triangular astigmatism with three axes (e.g. one point could
be seen as the Mercedes star due to the halos). It has a more minor affect on image
quality compared to coma.
C. Coma aberrations: Are caused when light rays from one edge of the pupil focuses
before those from the opposing edge. Visually the image may appear to have a tail like a
comet.
Coma aberration occurs with Keratoconus patients.
Ocular Aberration
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Perfect Eye
Coma
Spherical
Aberration
Quedrefoil >
< Trefoil

26. • We can measure the amount of the aberration
by using the aberrometer.
• Higher-order aberrations are so complex that
they cannot be improved with ordinary
eyeglasses or soft contact lenses. However, they
can be treated with rigid contact lenses, IOL,
and a special glasses can reduce the symptoms.
• Surgery such as traditional LASIK and
Keratoplasty (corneal transplant) can worsen
HOAs in the eye. Instead we can use (custom
wavefront LASIK) surgery.
Ocular Aberration
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Aberrometer