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Optics of Intraocular Lenses PowerPoint Presentation

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Description : Check out this medical PowerPoint presentation titled "Optics of Intraocular Lenses” by Dominic McHugh, MD FRCS.

This medical PowerPoint presentation is about intraocular lenses (IOLs), medical devices that are implanted inside the eye to replace the eyes natural lens when it is removed during cataract surgery. IOLs can also be used to correct refractive errors such as nearsightedness, farsightedness, and astigmatism. The optics of IOLs play a critical role in determining the visual outcomes for patients.

There are several types of IOLs available, including monofocal IOLs, multifocal IOLs, and toric IOLs. Monofocal IOLs have a single focal point, which means that patients will need to rely on glasses for near or distance vision. Multifocal IOLs have multiple focal points, which can provide patients with clear vision at both near and far distances without the need for glasses. Toric IOLs are designed to correct astigmatism, which is an irregular curvature of the cornea.

The optical design of IOLs can vary depending on the type of lens. Monofocal IOLs typically have a spherical design, which means that they have the same curvature across the entire lens surface. Multifocal IOLs, on the other hand, may have a diffractive or refractive design. Diffractive multifocal IOLs work by splitting the incoming light into multiple focal points, while refractive multifocal IOLs work by bending the incoming light at different angles to create multiple focal points.

Toric IOLs have a different optical design that incorporates a cylinder to correct astigmatism. The cylinder is added to the lens surface to compensate for the irregular curvature of the cornea.

In addition to the design of the lens, other factors can affect the optics of IOLs, including the size of the lens, the position of the lens in the eye, and the quality of the patients cornea. Optimal IOL selection and placement require careful consideration of these factors, as well as the patients individual visual needs and preferences.

Tags : intraocular lenses, IOLs, medical devices, cataract surgery, refractive errors, nearsightedness, farsightedness, astigmatism, Ophthalmology, Ophthalmology PowerPoint presentation

Published on : Jun 20, 2023 | Views : 2603 | Downloads : 4

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Slide 1-

Optics of Intraocular Lenses
Slide 2-

Cataract Surgery Cataracts are the second most common cause of bilateral vision impairment Used to remove patients own lens and replace with an artificial lens Most common elective surgery Can be done to change refractive power of the eye https://www.safetyandquality.gov.au/wp-content/uploads/2017/06/4.6-Cataract-surgery.pdf
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Aim To implant a lens which gives a clear image on the retina Most commonly aim for distance vision in both eyes Consider Corneal power Axial length Anterior chamber depth IOL position Astigmatism Tasks/working distance Previous refraction
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Cataract surgery- History/evolution Yanoff & Duker: Ophthalmology, 3rd ed Table 5-2-1, pg 394
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Cataract surgery- incisions Smaller incision sizes with improved technology. Results in decreased post-op astigmatism Laser incisions Image from Zeiss
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Capsulorhexis and phacoemulsification Front of the lens capsule is peeled away Removal of the clouded crystalline lens (cataract). Emulsification of the lens with an ultrasonic handpiece, and aspiration from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution, thus maintaining the anterior chamber, as well as cooling the hand piece.
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Live cataract surgery https://www.youtube.com/watch?v=SXh1XysbFmc
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Terminology Optic zone/optic Area used for seeing through Destination Where in the eye the IOL will be implanted Haptics Used to hold the lens in place in the capsular bag Modified C or solid flange Determine stability of implant Optic Haptic Square edge Orientation marker https://visioneyeinstitute.com.au/eyematters/trifocal-intraocular-lenses/
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Different lens options Incision Size Micro Incision Small Incision Enlarged Incision Colour Yellow (Violet or Blue blocker) Clear (UV Blocker) Material Silicone PMMA (rigid) Hydrophilic acrylic (foldable) Hydrophobic acrylic (foldable)
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IOL materials Polymethyl methacrylate (PMMA) 1st material used 1949 unable to fold thus require large incision Inert Used in 3rd world countries today as cheap Thin haptics Silicone IOLs - unable to fold Belucci 2013
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IOL Materials Hydrophobic acrylic able to fold for insertion Can distort and regain shape in seconds Injectable Glistenings Need to be centred well and require 2.2mm cut for insertion Hydrophilic acrylic Foldable for insertion Able to be inserted through sub 2mm Biocompatible Higher rate of PCO Possible risk of opacification with RD gas Range of designs and haptics
Slide 12-

IOL classification Belucci 2013
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Haptics 3 piece design- usually have c shaped haptics inserted into optic Single piece designs- range of shapes
Slide 14-

IOL manufacturing Can play a role in choice Consider edge design Injectable, pre-loaded lenses Optical side effects Glare- reflection Light scattering Aberrations https://www.rayner.com/news/rayner-intraocular-lenses-to-launch-their-first-preloaded-iol-product-c-flexr-advance-aspheric-at-the-escrs.html
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Edge design https://www.slideshare.net/sumeetagrawal524/intraocular-lenses-33174150
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Aberrations Moderate level aberrations are important to consider- spherical and coma Human eye cornea has positive spherical aberration (and very low coma aberration) which is usually corrected by the lens when young but lost as we get older Aberrations produce glare and lack of sharpness of vision Worse in dim conditions http://www.olympusmicro.com/primer/anatomy/aberrations.html
Slide 17-

Aberrations Spherical aberrations soften the contrast and blur the details
Slide 18-

Spherical aberration
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Asphericity - IOLs Spherical IOLs add to the positive SA induced by the cornea. If the optic position is not well aligned, other higher order aberrations, such as coma could occur, which would effect quality of vision Neutral Aspheric IOLs- do not create any spherical aberrations: they are suitable for all patients regardless of their cornea shape. They are not sensitive to decentration and tilt (as there is no residual asphericity). But they do not correct positive SA from the cornea, so there is potential loss of contrast Aspheric Aberrated IOLs (negative spherical aberration) correct the SA of an average cornea. They improve contrast sensitivity particularly when the pupil diameter is large. If the optic position is not well aligned, other higher order aberrations such as coma could occur, which would effect quality of vision. Corneal asphericity pre-surgery important
Slide 20-

Image by Zeiss
Slide 21-

Lens shape Lens tend to have greater curvature as immersed in aqueous n=1.33 rather than n=1 Shape can be meniscus, plano convex or biconvex- most common biconvex Different shapes place the effective power planes at different points
Slide 22-

Choosing a lens What do we want in the optic? What are the options? What power? Different lenses for different patients
Slide 23-

Effective lens position Distance lens is from the eye Varies from patient to patient If lens too close to cornea- myopic outcome Too far from cornea- hyperopic outcome
Slide 24-

Measurements In order to decide what power to insert a number of measurements are taken Corneal curvature Anterior chamber depth Axial length Newer machines now take into consideration corneal thickness and lens thickness
Slide 25-

Contact biometry https://www.reviewofophthalmology.com/article/increase-a-scan-accuracy-for-improved-outcomes http://www.accutome.com/b-scan-plus
Slide 26-

IOL master Can load specific lenses in to machine and it will determine which powers to order https://crstodayeurope.com/articles/2015-jul/physics-lesson-differences-in-pci-and-olcr-optical-biometry/
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Slide 28-

Power calculations Can’t directly measure the lens while its in the eye Range of formulas used SRK and SRK II- formula derived from lots of IOL implants links IOL power, axial length and average keratometry. Inaccurate for v long and short eyes All formulas stem from determining the total power by using two lenses P1 and P2 and their separation
Slide 29-

Basic formula
Slide 30-

Different formulas for different eyes Long and short eyes don’t have good results with SRK 2 Use other formulae for long and short lenses based on optical principles. Haigis HofferQ Holladay Updates to formulas- different generations (not just long and short) Barrett universal II Olsen Be careful promising no glasses as can still have optical surprise, particularly if previous corneal surgery
Slide 31-

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Slide 32-

Post Lasik/PRK Previous calculations assume cornea is spherical Corneal refractive surgery changes the cornea No longer normal relationship with axial length ACD doesn’t change Some of the newer biometers will take this into consideration
Slide 33-

Patient discussions Expectations Current vision- myopic, hyperopic History of laser surgery Glasses Visual tasks Discussion before referral https://www.health.mil/news/articles/2017/09/29/soldier-uses-school-project-to-combat-suicide?type=Infographics https://en.wikipedia.org/wiki/Censorship_in_Thailand http://www.smosh.com/smosh-pit/photos/21-weirdest-plastic-surgery-faces
Slide 34-

Optic types Monofocal Toric Multifocal Toric multifocal Accommodating
Slide 35-

Monofocal Most common One optical power Generally implanted for distance vision Requires glasses for reading/near vision Can do one eye distance and one near Trial in contacts Lack of depth perception http://eyepharma.co.za/contact-lenses/ocuflex-hydrophilic-monofocal-iol
Slide 36-

Toric IOLs IOLs can have toric front, back or both surfaces Used to correct astigmatism Axis on the lens marked for steep and flat meridia Rely on accurate insertion alignment during surgery Mark 0 and 180 on eye before putting block in for surgery More advanced systems becoming available that are markerless https://www.reviewofophthalmology.com/article/toric-iols-nailing-the-alignment Rotated IOL
Slide 37-

Toric multifocal IOLs https://www.healio.com/ophthalmology/journals/jrs/2011-9-27-9/%7B4a49034c-1f49-44e5-bc0f-58f4c89dff56%7D/comparative-analysis-of-clinical-outcomes-obtained-with-a-new-diffractive-multifocal-toric-intraocular-lens-implanted-through-two-types-of-corneal-incision
Slide 38-

Multifocal IOLs Splits incoming light into multiple focal points Usually 2 or 3 Gives acceptable distance/intermediate/near Aim to make patient as glasses free as possible Need a good cornea No macula issues No dry eye Potential drawbacks Glare, haloes, most adjust. Not for type A’s needing things perfect NOT FOR EVERYONE Not for fussy patients Want good depth of field, transmit as much light as possible, good VA at diff distances https://jaheedkhan.co.uk/should-i-have-a-multifocal-intraocular-lens-implant-for-my-cataract-surgery/
Slide 39-

Multifocal IOLs Optical compromise
Slide 40-

Multifocal IOLs
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Accommodating IOLs Haptics securely in place to keep lens in position Legs on the lens are designed so haptic moves slightly forward when ciliary muscle contracts May still need reading glasses http://www.tristateeye.com/crystalens.html
Slide 42-

https://www.austineye.com/intraocular-lenses/
Slide 43-

Options for when there is no capsule support Anterior chamber/Angle supported IOLs Used after complicated surgery Show endothelial and iris damage Avoid if glaucoma or shallow anterior chamber Scleral fixated posterior chamber IOL Iris-fixated posterior IOL Fixed to iris with sutures Intrascleral haptic capture
Slide 44-

Case study What sort of a discussion would you have with these patients? Decision is up to the surgeon. No right or wrong answer, and different doctors will do different things
Slide 45-

Bob 80 years old Significant cataracts. Mild AMD. Retired . Plays bowls. Worn glasses for the past 30 years. Refraction : R ) -2.00 /-3.50 x 180 = 6/18 L ) – 2.25 = 6/12 Possible IOL Options?
Slide 46-

Jane 35 years old c/o of photopsia Traumatic Right cataract following hit to eye with a tennis ball 5 years ago. Retina fine. R) -5.00 = 6/18 L ) plano Options ?
Slide 47-

Matthew 55yo C/o reduced VA due to cataract VA: 6/24 N8 6/12 N8 PHx : Lasik surgery for Hyperopia 8 years ago Right Eye Slight Amblyopia ( BCVA 6/12) Does not want to wear specs K readings R ) 42. 25/ 43.00 x 175 L ) 43.25 / 43.50 x 110 Options ?
Slide 48-

Resources General overview An Introduction to Intraocular Lenses: Material, Optics, Haptics, Design and Aberration. Bellucci 2013 Güell JL (ed): Cataract. ESASO Course Series. Basel, Karger, 2013, vol 3, pp 38–55 DOI: 10.1159/000350902 Ophthalmology viewpoint Ophthalmology: Yanoff & Duker Article on other IOLs http://www.ophthalmologytimes.com/modern-medicine-feature-articles/no-capsule-support-anterior-chamber-versus-posterior-chamber-iol