1. Edge profile of commercially available square-edge intraocular lenses
Mayank A. Nanavaty1 David J. Spalton James Boyce Anthony Brain John Marshall2
1. St. Thomas’ Hospital, London
2. King’s College, London
Financial interests: None

2. Aim
To analyze the sharpness of the posterior optic edge of intraocular lenses (IOLs) marketed with a ‘square-edge’ profile.
Methods
Seventeen IOLs of different designs and material all marketed as ‘square-edge’ IOLs
20 Diopter IOL of each selected
IOLs examined with environmental scanning electron microscopy

3. FEI Quanta 200F field emission gun environmental scanning electron microscope was used to examine IOLs
Parameters standardized for all IOLs
93.3 Pascal (0.7 torr),
Specimen temperature of 20oC,
Voltage of 15 KV
Magnification x 500
Average processing time 25 minutes
IOLs mounted using a simple microscope
Haptic excised
After a vigorous exercise with different IOL materials, we were able to standardized these parameter on FEI Quanta environmental scanning microscope, to produce the sharpest images with no effect on the material, in the minimum processing time.
Some IOLs required cutting of the
haptic and/or optic to view edge
Posterior edge appears always on the left

4. Measurement of Radius of Curvature of Posterior Optic Edge
Customised computer program measures
the local radius of curvature L L P P R r R r
The scans were than transferred to the physicist who used a customized computer program to evaluate the posterior optic edge sharpness. This was based on the principle that for every point p we could select two points at equal distances in such a way that they for a part of the circle and they make an angle of 45 degrees with the center of that circle and the radius of the curvature can than be calculated. Therefore, the sharper the optic edge, the smaller will be the radius of the circle.
Sharper optic edge = Smaller r
See details in J Cataract Refract Surg, April 2008.

5. Hydrophobic Acrylic IOLs
9.9µ
8.5µ
9.3µ
So, in the hydrophobic acrylic group, Alcon IQ, Natural and three piece had sharp posterior optic edges with radii less than 10U.
Alcon
AcrySof IQ
Alcon
AcrySof Natural
Alcon
AcrySof MA60AC

6. Hydrophobic Acrylic IOLs
8.3µ
19.9µ
AMO Sensar AR40e
Hoya AF-1(UY)

7. Hydrophilic Acrylic IOLs
15.9µ
14.3µ
B & L Akreos
B & L MI60
23.1µ
15.5µ
Bausch & Lomb Akreos and Akreos AO also has ounder optic edges with radii of >10u and lenstec Tetraflex has a radii the roundest posterior optic edge with the radii of >20U.
Lenstec Tetraflex
Rayner Superflex

8. Hydrophilic Acrylic IOLs
9.1µ
8.6µ
However, in the hydrophillic acrylic group, Humanoptic IOLs had sharpest posterior optic edges with radii of < 10U.
Human Optics 1CU
Human Optics MC611 MI-B

9. Silicone IOLs 8.3µ 7.6µ Bausch & Lomb Soflex SE
In the silicone IOL group all the IOLs had a sharp posterior optic edges with radii of < 10 U. These are the scans of Bausch & Lomb Soflex SE and SofPort AO...
Bausch & Lomb Soflex SE
Bausch & Lomb SofPort AO

10. Silicone IOLs 9.2µ 8.3µ 9.0µ AMO Clariflex AMO Tecnis Z9000 AMO
AMO clariflex, Tecnis and Tecnis multifocal also had a very sharp posterior optic edges
AMO
Clariflex
AMO
Tecnis Z9000
AMO
Tecnis ZM9000

11. Summary Hydrophobic Acrylic IOLs Hydrophilic Acrylic IOLs
Radii of curvature (µ)
Alcon AcrySof® SN60WF
Alcon AcrySof® SN60AT
Alcon AcrySof® MA60AC
AMO Sensar® AR40e
Hoya® AF-1(UY)
8.5
9.3
9.9
8.3
19.9
Hydrophobic Acrylic IOLs
Rayner® C-flex (thinnest ridge)
Rayner® C-flex (thickest ridge)
Rayner® Superflex (thinnest ridge)
Rayner® Superflex (thickest ridge)
Bausch & Lomb Akreos®
Bausch & Lomb MI60
HumanOptics® 1CU
HumanOptics® MC 611 MI-B
Tetraflex®
18.2
19.6
15.6
10.6
15.9
14.3
8.6
9.1
23.1
Hydrophilic
Acrylic IOLs
In summary, all the hydrophobic acrylic IOLs had a sharp posterior optic edge profile except Hoya, all the hydrophillic acrylic IOLs had a rounder posterior edge profile except Human optics IOLs. And all the Silicone IOLs had a very sharp posterior optic edge profile.
Bausch & Lomb Soflex®
Bausch & Lomb SofPort® AO
AMO Clariflex®
AMO Tecnis® Z9000
AMO Tecnis® ZM9000
8.3
7.6
9.2
9.0
Silicone IOLs

12. Conclusion
Commercially marketed ‘square edge’ IOLs differ in posterior edge sharpness.
Most hydrophobic acrylic and silicone IOLs have sharper posterior optic square edges compared to most hydrophilic acrylic IOLs. This probably reflects difference in manufacturing techniques.
The difference in the posterior optic edge profile may explain why some IOLs have relatively poor PCO performance and may explain why some IOL materials appear to have better PCO performance than others.
Hence, radii of curvature of posterior optic edges of all the hydrophobic and silicone IOLs were <10 U (except Hoya) and all the hydrophillic IOLs had a radii of curvature of > 10 U except human optics. This could be because the hydrophillic IOLs are lathe cut in a dehydrated state and than rehydrated which could lead to rounding to the edges.