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Chapter 9 Intraocular Lenses

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Chapter 9 Intraocular Lenses Aphakic IOL Implantation Older IOLs inflexible (e.g. PMMA), so larger incision was required Larger incision often led to significant (and ... – PowerPoint PPT presentation

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Title: Chapter 9 Intraocular Lenses


1
Chapter 9Intraocular Lenses
2
Aphakic IOL Implantation
Page 9.1
  • Older IOLs inflexible (e.g. PMMA), so larger
    incision was required
  • Larger incision often led to significant (and
    variable) post-surgical astigmatism
  • Newer designs are foldable allowing much smaller
    incisions
  • Most cataract extractions today are extracapsular
    (capsule remains intact) allows easy insertion
    of foldable implants

3
Early Anterior Chamber IOLs (1960s)
Fig 9.1 Page 9.1
  • Intracapsular cataract extraction
  • PMMA Iris Clip Lens placed in anterior chamber
  • Many iris-related problems iritis, pupil
    distortion, corneal endothelial cell loss

4
Posterior Chamber IOLs (1977)
Fig 9.2 Page 9.2
  • Extracapsular cataract extraction (capsule
    remains intact) now in vogue
  • Allowed posterior chamber implantation, initially
    in ciliary sulcus
  • Capsular bag soon took over as implant site of
    choice because of problems with ciliary sulcus
    implants (e.g. pigmentary glaucoma)

5
Fig 9.3 Page 9.2
Ciliary Sulcus
6
Fig 9.4 Page 9.3
Posterior Chamber IOL in Ciliary Sulcus
7
Sutured Haptic tied off and knot buried in
conjunctiva
Fig 9.5 Page 9.3
8
Fig 9.6 Page 9.4
Capsular Bag Implant
9
Fig 9.7 Page 9.4
IOL inside Capsular Bag
10
Fig 9.8 Page 9.4
Newer Capsular Bag Lenses
11
Phakic IOLs
Page 9.5
  • Emergence of phakic IOLs in mid-1980s, as
    biocompatible foldable materials became available
  • Phakic IOLs exclude the ciliary sulcus and
    capsular bag as implant sites
  • AC IOLs therefore returned
  • Had to overcome the previous iris-related
    problems with AC lens
  • Advantage over LASIK, PRK etc. ? reversible

12
Fig 9.9, Page 9.5
  • Iris claw lens (Artisan, 1998)
  • Not feasible with AC depth lt 3.2 mm
  • This impacted primarily the hyperopic pool
  • Unfortunate because hyperopes have lower success
    rate with corneal refractive surgery than myopes
  • Complications (e.g. endothelial cell loss, glare,
    etc.) remain but appear to be decreasing with
    newer designs

13
Posterior Chamber Phakic IOLs
Fig 9.10 Page 9.6
  • Collamer posterior chamber phakic ICL
    (implantable contact lens)
  • Implanted between iris and anterior crystalline
    lens
  • Contact with anterior lens causes anterior
    subcapsular cataract
  • Iris problems also occur
  • Best option for hyperopes
  • PC location means higher lens power than
    equivalent corneal power change with LASIK

14
IOLs and near Vision
Page 9.7
  • Multifocal intraocular lenses are the IOL
    equivalent of multifocal contact lenses
  • Poor track record until recently

15
Fig 9.12 Page 9.8
Array Multifocal Lens
  • Alternating distance and intermediate/near zones

16
Fig 9.13 Page 9.8
Accommodating IOLs
  • Humanoptics aphakic IOL
  • Capsular bag-fixated lens
  • Four flexible haptics that bend when constricted
    by capsular bag
  • Effect ? forward translation of lens
  • This increases total ocular power

17
Humanoptics Accommodating IOL
unaccommodated
accommodated
18
Post-operatively Adjustable IOLs
Page 9.7
  • Photosensitive silicone matrix polymerizes with
    UV exposure (a)
  • If central region polymerized (b) the chemical
    imbalance causes unpolymerized peripheral matrix
    to diffuse centrally
  • (c) result is increased IOL power

19
IOL Power Formulae
Page 9.10
  • Goal calculate the IOL power required for
    emmetropia
  • Early formulae based on two ocular variables
    only axial length and mean corneal power e.g.
    SRK I Formula
  • Outcome totally dependent on ultrasonography
    (ax?, or L) and keratometry estimate of total
    corneal power (K mean power)
  • Later variant SRK II addressed inaccuracies of
    SRK I at the extremes of axial length

20
Intraocular Implant Design
  • SRK I Formula

SRK Sanders-Retzlaff-Kraff (developers of
formula)
21
Implant Design Example
IOL with A value of 116.5 Patient K _at_ 90
43.75 D K _at_ 180 44.00 D ? mean K 43.875
D Axial length 24.03 mm
22
Intraocular Implant Design
  • The SRK II Formula allows for errors at the
    extremes of axial length with SRK I
  • Makes adjustments to IOL type constant, A

A1 A 3 axial lengths lt 20 mm A1 A 2 axial
lengths between 20 21 mm A1 A 1 axial
lengths between 21 22 mm A1 A axial lengths
between 22 24.5 mm A1 A ? 0.5 axial lengths gt
24.5 mm
23
Short Axial Length Example
Same IOL design with A value of 116.5 Patient
K _at_ 90 47.25 D K _at_ 180 48.75 D ? mean K
48.00 D Axial length 20.57 mm ? A1 A 2
(20-21 mm range)
using A ? 21.88 D
24
Page 9.10
Limitation of all 2-Variable Formulae
  • No allowance for anterior chamber depth
  • Example three patients, all with mean K (corneal
    power) 43.05 D and axial length 24.17 mm (?
    standard emmetropic eye)
  • Patient 1 AC depth 2.8 mm
  • Patient 2 AC depth 3.6 mm
  • Patient 3 AC depth 4.4 mm
  • Outcome of SRK I formula (II not needed for
    standard axial length) for capsular bag implant
  • Patient 2 emmetropic
  • Patient 1 (shorter AC depth) is now myopic can
    see OK to read, but distance blurred
  • Patient 3 (longer AC depth) is now hyperopic
    cannot see to read cannot see at distance (no
    accommodation)

25
Three-Variable Formulae (new variable AC depth)
  • SRK/T formula adds an iris location variable, ?
    allow for AC depth
  • Effect of IOL location?

Page 9.10
  • As AC depth increases, IOL power should increase
  • Likewise, IOL location (AC vs. ciliary sulcus vs.
    capsular bag) affects required power
  • AC implant longest dcornea ? IOL location ?
    lowest power
  • Ciliary sulcus shorter d ? higher power
  • Capsular bag another ?0.5 mm shorter again ?
    higher power again

26
Example of 3-Variable Formula, allowing for AC
Depth
Fig 9.16, Page 9.11
nIOL
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