1 / 24

Visual Optics

Page 3.34. Visual Optics. Chapter 3 Retinal Image Quality. Spherical Aberration. Higher SA (exit pupil). Lower SA (exit pupil). Calibration Sphere: “Power” vs. Incident Height. Myopic Real Cornea: “Power” vs. Incident Height. 54.00 D  46.91 D = 7.09 D. 50.75 D  44.71 D = 5.04 D.

alair
Download Presentation

Visual Optics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Page 3.34 Visual Optics Chapter 3 Retinal Image Quality

  2. Spherical Aberration Higher SA (exit pupil) Lower SA (exit pupil)

  3. Calibration Sphere:“Power” vs. Incident Height Myopic Real Cornea: “Power” vs. Incident Height 54.00 D  46.91 D = 7.09 D 50.75 D  44.71 D = 5.04 D

  4. Q2. Assuming the eye to have a spherical reduced surface, what change occurs in LSA when pupil diameter increases from 2 mm to 6 mm? (a) LSA triples (b) LSA increases 6 (c) LSA increases 9 (d) LSA increases 27

  5. Spherical Aberration: Longitudinal (LSA) and Transverse (TSA) Page 3.46 TSA “captured” on a screen. e.g. retinal PSF for axial object Figure 3.38 – LSA and TSA for a reduced eye (spherical reduced surface) with large pupil diameter. Object is a distant axial point source. The waist of least aberration (WOLA) is well to the left of the paraxial focus. Spherical aberration greatly exaggerated.

  6. LSA and TSA Page 3.47 Figure 3.39 – (a) Relationship between LSA and TSA. fm = marginal focal length; fp = paraxial focal length. Appearance of screen image at the paraxial focus also shown. (b) Using similar triangles to relate LSA to TSA in terms of pupil diameter (y);  = angle subtended by marginal ray (at optical axis). OBJ OBJ

  7. SA and Real Eyes Page 3.48 • Real eyes do not have spherical corneas or crystalline lenses • Experimental results show positive corneal SA and negative lenticular SA • Positive corneal SA < that predicted for spherical cornea • SA also differs between myopes and hyperopes Why would hyperopes have higher corneal SA? Less aspheric corneas (less peripheral flattening). Reason? Unknown

  8. Page 3.49 Figure 3.38 – (a) Spherical cornea (b) Aspheric cornea (c) Aspheric rays (_______) vs spherical rays (- - - - - - - -) Schematic Eye prediction Real Eye example

  9. Figures will be provided Ocular Spherical Aberration Role of Accommodation

  10. Wavefront Map Retinal PSF • Wavefront Map(defocus removed,each map contour = 1 µM step. Color scale in µM) • wave aberration increases with accommodation • increase greater near center of pupil (esp. for highest accom). • PSF for 8 mm Pupil(defocus excluded) • Image spread increases with accommodation •  retinal image quality decreases as the eye accommodates. 0 D Accom 1.4 D 3.9 D 5.9 D 10.9 D

  11. Wavefront Error: Fully Accommodated Eye RMS error = error averaged across exit pupil RMS error = error averaged across exit pupil

  12. Q3. Near miosis is the pupil constriction that occurs as the eye focuses at near. How would near miosis affect retinal image quality? (a) improves because of reduced wavefront error (b) no change (c) gets worse because less light is admitted through the pupil (d) improves because negative corneal SA is decrease

  13. Retinal PSF vs Pupil Diameter: Fully Accommodated Eye 3 mm 4 mm 5 mm 6 mm 7 mm 8 mm

  14. Spherical Aberration: Trend with Accommodation Total ocular SA becomes progressively more negative with accommodation

  15. Ocular refractive power variation across pupil (zones color-coded) for various accommodative states between 0 and 9 D • As accommodation increases, the discrepancy between central and peripheral power change becomes larger • Consistent with an increase in negative spherical aberration contributed by the crystalline lens as accommodation increases

  16. Ocular SA and Refractive Surgery Page 3.50 If pupil diameter exceeds ablation zone diameter  SA Larger ablation zone means deeper ablation LASIK produces similar problems at the edge of the ablated zone Replacing a non-ablated flap over the reshaped stroma is also a problem, often introducing higher order aberrations Figure 3.41 – Light ray traveling through the center of the pupil and two rays either side are shown refracting through the flattened (ablated) corneal zone. Another ray immediately either side of the ablated zone refracts at a significantly sharper angle through the now steepest corneal curvature. This causes considerable positive spherical aberration

  17. Q4. In typical real eyes, the net effect of positive spherical aberration on retinal image quality is less than that predicted by a schematic eye with spherical refracting surfaces because: (a) an aspheric cornea produces less SA (b) lenticular SA is negative (c) an aspheric cornea produces less SA and posterior corneal power is negative (d) an aspheric cornea produces less SA and lenticular SA is negative

  18. Coma Page 3.52

  19. Coma Page 3.52 Comatic image ofa point Most complex monochromatic aberration “Off-axis” version of spherical aberration Asymmetric, comet-shaped, image very detrimental to overall image quality

  20. Coma Page 3.52 Snell’s Law:n sin i = n sin i Greater wavefront curvature above axis: converges marginal image rays below the paraxial image point Lower wavefront curvature below axis: leaves too little convergence for marginal rays to reach the paraxial image point Figure 3.42 (bottom) – Seidel positive coma ray pattern for a spherical refracting surface

  21.  Reference Planes for Asymmetric Aberrations Page 3.53 x0 x Tangential Plane: plane passing through optic axis in direction of OA point contains chief ray (pupil ray) from OA point and optic axis perpendicular to tangential plane; also passing through optic axis Sagittal Plane:

  22. Coma: Tangential & Sagittal Planes Page 3.54 Greatest wavefront asymmetry in tangential plane Object presents the most asymmetric profile in this plane Snell’s Law:n sin i = n sin i Least wavefront asymmetry in sagittal plane All sagittal rays focus in the tangential plane Figure 3.44 – Coma produced by a spherical refracting surface (e.g. the cornea) for a below-axis object point in the tangential plane (top) and sagittal plane (bottom).

  23. Coma: 45 Oblique Planes Page 3.55 45 oblique planes focus right and left of the tangential plane Stronger refraction above axis; weaker below-axis Figure 3.45 – Coma produced by a spherical refracting surface for a below-axis object point in oblique incident planes, 45 from vertical (top); +45 from vertical (bottom).

  24. Coma – Composite Page 3.56 Filling in all other oblique planes the result is a series of comatic circles Each circle corresponds to a given incident height at the aperture ( value) Figure 3.46 – View looking “through” the spherical refracting surface toward the image plane, showing the parts of the comatic (comet-shaped) image produced by tangential, sagittal and 45 oblique meridians.

More Related