Michael J. Simpson, Ph.D.Simpson Optics,

Arlington, Texas, USA www.SimpsonOptics.com

Lens Capsule Effects on Negative Dysphotopsia, Visual phenomena, and Refractive Error

Presbyopia 2019, Paris, FranceFriday, 13 Sept. 2019

ESCRS 2019

Introduction

• The lens capsule is the preferred location for an IOL• But it shrinks, and can opacify• Capsule characteristics can be gleaned from implants

• Visual phenomena can be affected by the capsule• “Negative Dysphotopsia” reported with IOLs since 2000

• Peripheral “dark shadows” on temporal side• Patients may sketch something like this• Saluting like a soldier obscures it• Visible mainly with small pupils

• Positive dysphotopsia• Light reflected by the edge• Light missing the IOL

2

Comparing Crystalline lens to IOL

3

IOL

Crystalline lens

Simpson MJ, Muzyka-Woźniak M. J Cataract Refract Surg 2018; 44:459–465

• Same eye, preop and postop• Overlaid OCT images• Crystalline lens• All light passing through pupil is imaged

by the lens• IOL has small lens diameter• Causes vignetting of main image at large

angles (dark in periphery)• IOL has gap between iris and IOL• Average gap about 0.5 mm• JCRS paper 2018

Capsule clarity

• The capsule surrounding an IOL may not be clear• Soemmering’s ring was very common with early

IOLs, and this is still seen• Opacity affects light bypassing the IOL• Light scatters into shadow region• Probably the reason shadows not reported initially

•Modern IOLs and surgery can lead to clear capsules• Haze generally increases over time• Emphasis has been on PCO• Peripheral capsule not normally

evaluated

4

From Apple DJ, Influence of intraocular lens material and design on postoperative intracapsular cellular reactivity. Tr Am Ophth Soc 2000;98:257-283

Capsule Contraction with IOLs

• Haptics were angulated for early IOLs• To prevent iris capture• And to press on the bag to postpone PCO

• Uncertainty in power prediction• Forces needed were unclear

• It turned out that PMMA open-loop haptics were flattened by the capsule• PMMA haptics thermally reform• This does not happen to polypropylene• Single-piece haptics are also planar

• The capsule support determines the IOL location• at about 45 % of crystalline lens thickness

5

IOL at 0.45 of crystalline lens thickness

Negative Dysphotopsia: View from Above of Raytrace into Right Eye

6

Rays enter eye at large angle

• Think of this as your own right eye• At large angles the image is on the left

near the nose• Just behind the visible sclera

• The IOL is small so eventually no light enters it • The main image goes dark• Called “vignetting”

• Light can also miss the IOL• This visual region was just never really

considered before for IOLs

Main image goes dark because light misses lens at larger angles

Negative Dysphotopsia: Rescaling the Retina to Object Space

7

• Envisage image on polar plot in object space• Need to scale the retina, not input angles

• input beam can split• Where does the patient perceive the light to be,

not where it comes from

• Angle at 2nd nodal point highly linear to 700

• Originally used 1:1 for all angles• Recently modeled 70 year old crystalline lens• Confirms droop at large angles• This scaling is difficult, and unknown

Simulated Images for Bright Peripheral Object

• Ganzfeld illumination• No object structure

• Rays recorded on retina in Zemax• Location and intensity • Adjusted for Fresnel reflections and

pupil ellipticity• Rays added to image in Matlab

• Scaled back to polar plot in object space

• The shadow visible for small pupils is eliminated as the pupil expands• Consistent with clinical thinking

8

Narrow strips of peripheral intensity, illustrating effect of pupil diameter changes

Intensity changes across image

Simpson MJ, Simulated images of intraocular lens negative dysphotopsia and visual phenomena, J Opt Soc Am A; 36:B44-B51 (2019)

Effect of Capsule Scattering on the Shadow

• Scattering added when calculating images • 2.5 mm diameter pupil• Simplified calculation• 50% scattering, with increasing scattering

diameter• The shadow fades with increased scattering

9

Simulated Text on Peripheral Retina

• Peripheral text used as light source• Demonstrates characteristics in a clearer manner

• Cannot use standard convolution methods• Image created point by point• Simplified here using just horizontal points

• 2.5 mm pupil

10

Illuminated object

Image region on retina is projected out to object space

Object

Image

The “D” appears twice, which is something the split beam indicates

The more peripheral “D” is larger because it is not focused by the IOL. The light also comes from a lower visual angle

Effect of pupil dilation (1:1 scaling)

11

Comparing Phakic and pseudophakic peripheral images

• Using Revised scaling• 2.5 mm pupil• Full image calculation

12

70 year old phakic eye

Pseudophakic eye

Angles to 1200 to show the “D”, but actual scaling of eye is unknown.

Upper limit is thought to be 1100, but there are no real clinical data.

“Bothersome” Dysphotopsias

• “Positive dysphotopsia” from total internal reflection at lens edge• Night-time, large pupil• Arc of light near fovea • Appears and disappears as eye moves

• Moves away from light source • at twice the speed

• “Negative dysphotopsia” from vignetting• Bright illumination, small pupil• Shadow could suddenly appear with pupil

constriction

• No solid clinical proof for these

13

Edge not hit so no reflection

Cylindrical edge reflects concentrated light near fovea

Most light goes through edge, and any reflections are not foveal

Shadow can rapidly appear with modest pupil changes

Negative Dysphotopsia

Positive Dysphotopsia

Lightsource

Reflection

• IOL design details rarely published• Lower index IOLs may have reduced optic surface• Permits smaller incisions

• Silicone lenses have more bulk• Extent of the focused image, and visual

phenomena, may vary

IOL Style may have an Effect on Dysphotopsia

14

Sketches based on Das, Werner, Collins, Hong JCRS 2019

IOL Cross-sections

High index acrylic

Low index acrylic

Low index Silicone

Conclusions

• “Vignetting” highly likely to be primary cause of dark shadows• Main image goes dark with small pupil• Light missing IOL rapidly eliminates shadow as pupil opens

• Generally people do not complain of peripheral phenomena• Phenomena are linked to a source and not noticed• IOL edge reflection onto fovea is specific problem• “Bothersome” aspect of dark shadows not yet established

• Capsule shrinkage seems reliable and beneficial for conventional IOLs•Many things are just not being evaluated at the moment• angles, pupils, retinal scaling, the iris, peripheral capsule, etc

• Zemax makes everything about these evaluations complicated

15