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ASTIGMATIC
LENSES
OPTOM FASLU MUHAMMED
ASTIGMATIC LENS
In an astigmatic lens, all the meridians do
not have the same curvature and a point
image of a point object cannot be formed.
The lens effectively gives a minimum
power in one direction, gradually
changing to a maximum power in the
other, at right angle to the first.
Astigmatic lens
 There are two types of astigmatic
lenses, namely
-Cylindrical lenses
-Toric lenses
CYLINDRICAL LENSES
Cylindrical lenses have one plane
surface and the other curved surface
forming the part of a cylinder.
Thus, in one meridian the lens has
no vergence power which is known
as the axis of the cylinder.
The axis of a cylinder is
always at right angles to the
power meridian of the
cylinder.
In the meridian at right angle to the axis,
the cylinder acts as a spherical lens.
The total effect is the formation of a line
image of a point object. This is called
focal line. It is parallel to the axis of the
cylinder.
Astigmatic lens
NOTATION FOR CYLINDER LENSES AND
ORIENTATION OF AXIS
ORIENTATION OF AXIS
Astigmatic lens
A lens with purely cylinder power would
be described as, say – 4.00Dcyl(diopter
cylindrical)
Angles up to 180 are used for the axis of
cylinder, the full 360° protractor is only
required for the base direction of prism.
When describing a horizontal
cylindrical axis, it is conventional to
use the angle 180°, rather than zero,
ORIENTATION OF
CYLINDRICAL AXES ON A
PROTRACTOR
ORIENTATION OF CYLINDRICAL
AXES
 A good way to recognize cylindrical
axes from dispenser’s side is to view
the back of your left hand; the thumb
will point to the zero degree.
Thumb will point to zero degrees
TORIC LENSES
Toric lenses, also known as sphero-
cylinder lenses can be explained as
spherical lens that has been placed in
contact with a plano-cylinder lens.
Since a plano-cylinder lens has no power
along its axis meridian, the power along
the axis meridian of the combination
must result from spherical element alone.
The power along the other principal
meridian of the lens, at right angles to the
axis meridian of the cylinder surface, is
the sum of the sphere and cylinder.
Under the rotation test, it exhibits
scissor movement in the same way as a
plano-cylindrical lens and under the
movement test ; it exhibits movement
along each of its principal meridians.
The power of a sphero-cylindrical
lens is expressed by stating the
power of the spherical component
first, followed by the power of the
cylindrical component, and finally
the direction of the cylindrical axis.
Thus, the specification
– 3.00/– 2.00 × 90º
OPTICAL CROSS
REPRESENTATION OF
– 3.00/– 2.00 × 90°
It signifies that spherical
component of the lens is – 3.00D
The cylindrical component is –
2.00DC
The axis of the cylindrical
surface lies along the 90º
meridian.
On representing the power of the
sphero-cylindrical lens by means of
optical cross, the principal meridians
show – 3.00D on vertical meridian
and – 5.00D on the horizontal
meridian.
STURM’S CONOID
STURM’S CONOID
The pencil of light that results from refraction
at an astigmatic lens does not focus as a point,
the interval between two line foci is called the
‘Interval of Sturm.
The best focusing occurs somewhere inside the
interval of Sturm. This point is called the
‘Circle of least confusion.
The complete envelop of the light
near the circle of least confusion is
called the ‘Sturm’s Conoid.
DETECTION OF LENS
 Trial lens hand neutralizationTrial lens hand neutralization
 Lensometer / FocimeterLensometer / Focimeter
 Geneva lens measure or Lens clockGeneva lens measure or Lens clock
DETECTION OF
CYLINDRICAL LENS
In order to determine the cylinder lens and to
detect its dioptric strength.
Hold the lens a few inches away from your
eyes.
 sight a straight lined object, such as window or
the door frame.
Rotate the lens slowly as you would turn a
steering wheel – first to the right (clockwise),
then to the left (anti-clockwise)
If a section of the door frame appears slanted,
it establishes that the lens under examination is
a cylindrical lens. This is called “scissors like
movement.
PLANO-CYLINDRICAL
Now, neutralize both the meridians separately.
If the movement in one meridian is nil, it is a
plano-cylindrical lens and nil movement
meridian is taken as the axis of the lens.
SPHERO-CYLINDRICAL LENS
 If both the meridians show movement, it is
a sphero - cylindrical lens.
 The weaker movement meridian is taken
as the axis of the lens under observation.
 Neutralize both the meridians as before to
determine exact spherical and cylindrical
elements.
TRIAL LENS HANDTRIAL LENS HAND
NEUTRALIZATIONNEUTRALIZATION
 For a toric lens, rotational movementFor a toric lens, rotational movement
is used to find the axisis used to find the axis
 If observe “against movement” -If observe “against movement” -
use minus cylinder axis.use minus cylinder axis.
 If observe “with movement” - useIf observe “with movement” - use
plus cylinder axis.plus cylinder axis.
TRIAL LENS HAND NEUTRALIZATIONTRIAL LENS HAND NEUTRALIZATION
 For a toric lens, rotational movement isFor a toric lens, rotational movement is
used to find the axisused to find the axis
Astigmatic lens
TRIAL LENS HAND NEUTRALIZATIONTRIAL LENS HAND NEUTRALIZATION
 Toric lensToric lens
LENSOMETER
Lensometer can also be used to determine
the lens power of an astigmatic lens.
THANK
UUU……

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Astigmatic lens

  • 2. ASTIGMATIC LENS In an astigmatic lens, all the meridians do not have the same curvature and a point image of a point object cannot be formed. The lens effectively gives a minimum power in one direction, gradually changing to a maximum power in the other, at right angle to the first.
  • 4.  There are two types of astigmatic lenses, namely -Cylindrical lenses -Toric lenses
  • 5. CYLINDRICAL LENSES Cylindrical lenses have one plane surface and the other curved surface forming the part of a cylinder. Thus, in one meridian the lens has no vergence power which is known as the axis of the cylinder.
  • 6. The axis of a cylinder is always at right angles to the power meridian of the cylinder.
  • 7. In the meridian at right angle to the axis, the cylinder acts as a spherical lens. The total effect is the formation of a line image of a point object. This is called focal line. It is parallel to the axis of the cylinder.
  • 9. NOTATION FOR CYLINDER LENSES AND ORIENTATION OF AXIS
  • 12. A lens with purely cylinder power would be described as, say – 4.00Dcyl(diopter cylindrical) Angles up to 180 are used for the axis of cylinder, the full 360° protractor is only required for the base direction of prism.
  • 13. When describing a horizontal cylindrical axis, it is conventional to use the angle 180°, rather than zero,
  • 15. ORIENTATION OF CYLINDRICAL AXES  A good way to recognize cylindrical axes from dispenser’s side is to view the back of your left hand; the thumb will point to the zero degree. Thumb will point to zero degrees
  • 16. TORIC LENSES Toric lenses, also known as sphero- cylinder lenses can be explained as spherical lens that has been placed in contact with a plano-cylinder lens.
  • 17. Since a plano-cylinder lens has no power along its axis meridian, the power along the axis meridian of the combination must result from spherical element alone. The power along the other principal meridian of the lens, at right angles to the axis meridian of the cylinder surface, is the sum of the sphere and cylinder.
  • 18. Under the rotation test, it exhibits scissor movement in the same way as a plano-cylindrical lens and under the movement test ; it exhibits movement along each of its principal meridians.
  • 19. The power of a sphero-cylindrical lens is expressed by stating the power of the spherical component first, followed by the power of the cylindrical component, and finally the direction of the cylindrical axis. Thus, the specification – 3.00/– 2.00 × 90º
  • 20. OPTICAL CROSS REPRESENTATION OF – 3.00/– 2.00 × 90°
  • 21. It signifies that spherical component of the lens is – 3.00D The cylindrical component is – 2.00DC The axis of the cylindrical surface lies along the 90º meridian.
  • 22. On representing the power of the sphero-cylindrical lens by means of optical cross, the principal meridians show – 3.00D on vertical meridian and – 5.00D on the horizontal meridian.
  • 24. STURM’S CONOID The pencil of light that results from refraction at an astigmatic lens does not focus as a point, the interval between two line foci is called the ‘Interval of Sturm. The best focusing occurs somewhere inside the interval of Sturm. This point is called the ‘Circle of least confusion.
  • 25. The complete envelop of the light near the circle of least confusion is called the ‘Sturm’s Conoid.
  • 26. DETECTION OF LENS  Trial lens hand neutralizationTrial lens hand neutralization  Lensometer / FocimeterLensometer / Focimeter  Geneva lens measure or Lens clockGeneva lens measure or Lens clock
  • 27. DETECTION OF CYLINDRICAL LENS In order to determine the cylinder lens and to detect its dioptric strength. Hold the lens a few inches away from your eyes.  sight a straight lined object, such as window or the door frame.
  • 28. Rotate the lens slowly as you would turn a steering wheel – first to the right (clockwise), then to the left (anti-clockwise) If a section of the door frame appears slanted, it establishes that the lens under examination is a cylindrical lens. This is called “scissors like movement.
  • 29. PLANO-CYLINDRICAL Now, neutralize both the meridians separately. If the movement in one meridian is nil, it is a plano-cylindrical lens and nil movement meridian is taken as the axis of the lens.
  • 30. SPHERO-CYLINDRICAL LENS  If both the meridians show movement, it is a sphero - cylindrical lens.  The weaker movement meridian is taken as the axis of the lens under observation.  Neutralize both the meridians as before to determine exact spherical and cylindrical elements.
  • 31. TRIAL LENS HANDTRIAL LENS HAND NEUTRALIZATIONNEUTRALIZATION  For a toric lens, rotational movementFor a toric lens, rotational movement is used to find the axisis used to find the axis  If observe “against movement” -If observe “against movement” - use minus cylinder axis.use minus cylinder axis.  If observe “with movement” - useIf observe “with movement” - use plus cylinder axis.plus cylinder axis.
  • 32. TRIAL LENS HAND NEUTRALIZATIONTRIAL LENS HAND NEUTRALIZATION  For a toric lens, rotational movement isFor a toric lens, rotational movement is used to find the axisused to find the axis
  • 34. TRIAL LENS HAND NEUTRALIZATIONTRIAL LENS HAND NEUTRALIZATION  Toric lensToric lens
  • 35. LENSOMETER Lensometer can also be used to determine the lens power of an astigmatic lens.