Prof.Paolo Vinciguerra, M.D. 1, 2 Antonio Calossi 4 Riccardo Vinciguerra, M.D. 1-3 1 Humanitas University 1 Humanitas Clinical and Research Center IRCS 2 Columbus, Ohio State University 3 University of Insubria, Varese CATARACT SURGERY AND DEPTH OF FIELD 4 (D.O.F.)
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 Small Pupil Large Pupil
Sph. Aberration does not increase D.O.F. Negative Sph. Ab. Defocus toward the inside No Sph. Ab. Defocus toward the outside Positive Sph. Ab.
D.O.F. and SPh. Ab. 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 +0 D +1D + -2D 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 outfocus 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 = f 2 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
Thank you for your attention 1 Associate 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