Title: Chapter 9 Intraocular Lenses
1Chapter 9Intraocular Lenses
2Aphakic 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
3Early 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
4Posterior 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)
5Fig 9.3 Page 9.2
Ciliary Sulcus
6Fig 9.4 Page 9.3
Posterior Chamber IOL in Ciliary Sulcus
7Sutured Haptic tied off and knot buried in
conjunctiva
Fig 9.5 Page 9.3
8Fig 9.6 Page 9.4
Capsular Bag Implant
9Fig 9.7 Page 9.4
IOL inside Capsular Bag
10Fig 9.8 Page 9.4
Newer Capsular Bag Lenses
11Phakic 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
12Fig 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
13Posterior 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
14IOLs and near Vision
Page 9.7
- Multifocal intraocular lenses are the IOL
equivalent of multifocal contact lenses - Poor track record until recently
15Fig 9.12 Page 9.8
Array Multifocal Lens
- Alternating distance and intermediate/near zones
16Fig 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
17Humanoptics Accommodating IOL
unaccommodated
accommodated
18Post-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
19IOL 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
20Intraocular Implant Design
SRK Sanders-Retzlaff-Kraff (developers of
formula)
21Implant 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
22Intraocular 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
23Short 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
24Page 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)
25Three-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
26Example of 3-Variable Formula, allowing for AC
Depth
Fig 9.16, Page 9.11
nIOL