4 cataract surgery and depth of field (d.o.f.) · cataract surgery and depth of field (d.o.f.)...

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 paolo.vinciguerra@humanitas.it

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

info@vincieye.it

Thank you for your attention