4 cataract surgery and depth of field (d.o.f.) · cataract surgery and depth of field (d.o.f.)...
TRANSCRIPT
CATARACT SURGERY
AND DEPTH OF FIELD
(D.O.F.)
Prof.Paolo Vinciguerra, M.D.1, 2
Antonio Calossi 4 Riccardo Vinciguerra, M.D.1-3
1Humanitas University 1 Humanitas Clinical and Research Center IRCS
2Columbus, Ohio State University 3University of Insubria, Varese
4
Depth of Focus Factors
An image can be considered to be made
up of an array of points
The finite size of the pixels, the photographic
grain, or the photoreceptor clusters
determine the fineness of detail of the
recorded image
Depth of Focus Factors
This means that a blur of a focused point
will be tolerated if it is no bigger than the
size of the receptor
Depth of Field and Depth of
Focus Due to similarities in name and nature,
depth of field and depth of focus are
commonly confused concepts
Depth of Focus
The amount of blur in diopters (or
millimeters from the retina) that will be
tolerated or go unnoticed
Depth of Field
The distance range, in object space,
that an object can move (toward or
away from a fixed focus optical
system) and still be considered in focus
There are two ways to explain:1°
Formulas!
Immages 2°
Factors affecting DOF of the Eye
Pupil size
the lens f-number
D.O.F. is pupil size related
Pupil size:
pupil dilated shallow D.O.F., small pupil
wide D.O.F
Pupil size DOF example
Large Pupil Small Pupil
Large pupil induce not only small D.O.F but
also haloes
Factors affecting DOF of the Eye
Axial length
the lens focal length
Factors affecting DOF of the Eye
Visual acuity
circle of confusion
Depth of focus in normal eye
D.O.F. and focus distance law
The second element affecting depth
of field is the distance of the subject
from the lens
We can adjust the DOF by changing
that distance.
The closer an object is to the lens (and
the focus is set on that object) the
shallower the DOF.
The farther away an object is and
focused on, the deeper the DOF
The two ways to change the
depth of field 1°Pupil size
2° Focus distance
Why Kamra can not fix all?
Explained by Formulas
Explained by images…
Sharpness, not D.O.F., is better
with large pupil IF no H.O.A.
Large Pupil Small Pupil
In astronomy telescope are
used at large aperture for max
performance
Large aperture
Small aperture
In the eye is the same.
If no HOA PSF better with larger
aperture
Large Pupil Small Pupil
Sph. Aberration does not
increase D.O.F.
Negative Sph. Ab.
Positive Sph. Ab.
No Sph. Ab.
Defocus toward the inside
Defocus toward the outside
D.O.F. and SPh. Ab.
+1D + -2D
+0 D
• A slightly negative
Spherical aberration value
provides good distance
vision and a fair
compromise for near vision
• The optical power at the
center is slightly myopic
(narrow pupil provides a
good near vision)
• When the pupil is mesopic
or scotopic SA is zero or
slightly positive increasing
night vision
Power in pupillary field
H.O.A. and
D.O.F
• The image is sharp
when pefect focused
• What happens to the
area that are out of
focus?
• The image degrades
progressively
• The degradation is different when HOA
are present
• The quality of the out-
focus quality is called bokeh
Focus distance
and D.O.F
D.O.F. is influenced by sensor
size (retina)
Small animal = small eyes
has greater D.O.F
High myopias (large sensors)
has shallow DOF
High Hyperops (small sensors)
has large DOF
DOF 1/3 in front of focus point , 2/3
behind it!
1/3 2/3
What is Hyperfocal?
Definition 1
The hyperfocal distance is
the distance beyond which
all objects are acceptably
sharp, for a lens focused at
infinity.
What is Hyperfocal?
Definition 2
The hyperfocal distance is the closest distance at which a optical system can be focused while keeping one object at infinity acceptably sharp.
When the lens (eye) is focused at that distance from half of the hyperfocal distance out to infinity will be acceptably sharp
Using Hyperfocal
The closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp; that is, the focus distance with the maximum depth of field. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp
The reciprocal of hyperfocal distance should be the RX target of IOL power calculation
D.O.F. and hyperfocal
In this example for a given pupil
size (and sensor size) when
hyperfocal distance is set we will
have everything in focus from
flowers to infinity
Hyperfocal distance
formula
H = f2
Nc
In photography hyperfocal is widely used and lens has indication for it
Near Optimization
Far optimization
WHICH IS THE BEST USE FOR US?
Hyperfocal, cataract, Biometry
Biometry in cataract can be set for 0 D
or emmetropia (infinity) or -2.5 D (near
vision
When a biometry is set to 0 D we waste
2/3 of DOF
When is set to-2.5 D the DOF is extremely
small
New approach
What if we use hyperfocal in
cataract surgery?
We can move the wasted DOF
beyond infinity using it for a better
vision at closer distance
Example 1
0 D Biometry note 2/3 of DOF is
beyond infinity
DOF
Example 2
-2.5 D Biometry
DOF
Example 3
Hyperfocal from 80 cm to 4 m
DOF
IOL, cataract and D.O.F.
When we perform cataract
surgery, we can optimize
refractive outcomes by targeting
specific focal points. This allows
our patients the benefit of
reduced dependence on glasses
as well as removal of the
cataract.
D.O.F gives a more cofortable view
Same Sharpness different D.O.F.
sharpness perception is linked to D.O.F.
What I did ( with a strong contribute of Calossi)
to make your life easy…
a D.O.F. calculator for cataract biometry
If you are interested write to me at [email protected]
Pupil during near vision become smaller…
Clear Vision Range
0,10 1,00 10,00
Distance (m)
1,02 1,69 5,00
PP PF PR
rx target -0,59 D
1Associate Professor Ophtalmology, Department of
Biomedical Sciences-Humanitas University.
Director Eye Centre- Humanitas Research Hospital 2 Visiting Professor Columbus, Ohio State University
3 Eye Centre- Humanitas Research Hospital
Thank you for your attention