Chapter 9 Intraocular Lenses

1. Chapter 9Intraocular Lenses

2. Page 9.1 Aphakic IOL Implantation • 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. Staar Lens Implanted in Capsular Bag Staar Lens (foldable silicone) Fig 9.8 Page 9.4 Newer Capsular Bag Lenses

11. Page 9.5 Phakic IOLs • 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 < 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. Fig 9.10 Page 9.6 Posterior Chamber Phakic IOLs • “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. Page 9.7 IOLs and near Vision • 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. Page 9.7 Post-operatively Adjustable IOLs • 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. Page 9.10 IOL Power Formulae • 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. IOL power for emmetropia Constant based on IOL type Axial length in mm Average total corneal power based on keratometry 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 @ 90 = 43.75 D K @ 180 = 44.00 D  mean K = 43.875 D Axial length = 24.03 mm

22. The SRK II Formula allows for errors at the extremes of axial length with SRK I • Makes adjustments to IOL “type” constant, A: Intraocular Implant Design A1 = A + 3 axial lengths < 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 > 24.5 mm

23. Short Axial Length Example Same IOL design with “A” value of 116.5 Patient: K @ 90 = 47.25 D K @ 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