O&O mdc Ltd.

1West Street, Lewes,
East Sussex, BN7 2NZ, U.K.
Tel: +44 (0)745 204 3401

O&O mdc s.r.l.

"Eden Business Park"
Via di Grotte Portella 28-34
00044 Frascati (RM) – Italy
Tel: +39 06 9401 6099

 

IOL POLYMERS


O&O IOL-Moulded Blanks


O&O IOL-Moulded Blanks


“O&Omdc”is an IOL process engineering company, which also specializes in the manufacture and supply of IOL disposable delivery systems, lens packaging, semi-finished IOLs and Half-Moulded polymers for being used by the IOL industry only.

“O&Omdc”has worked to further Research and Development into the advancement of new IOL polymers using Half-Moulded system for IOLs. The goal of “O&Omdc”is to provide the highest quality IOL-Moulded Blanks in line with our customers’ needs and expectations.


“O&O mdc” IOL-Moulds Manufacturing Specifications:


“O&Omdc” IOL-Moulds can be manufactured with various shapes for haptics and optic depending of customer’s specifications but “O&Omdc”also proposed a standard shape as follow:

O&O IOL-Moulded Blanks

Raw Material INCI Name:

Cyclo Olefin Polymer

CAS Number:

26007-43-2


O&O IOL-Moulded Blanks
Specifications: Specification with Tolerances:
External Diameter: 13.35 +0/-0.04 mm
Slanted Haptic Diameter (on lens): 10.0 ± 0.1 mm
Slanted Angle (on lens): 5° ± 0.2°

Optical Diameter (on lens):

 
- From +3.0 D to +6.0 D
- From +6.5 D to +10.5 D
- From +11.0 D to +15.0 D
- From +15.5 D to +19.5 D
- From +20.0 D to +24.0 D
- From +24.5 D to +28.5 D
- From +29.0 D to +33.0 D
- From +34.0 D to +40.0 D
5.8 ± 0.05 mm
5.8 ± 0.05 mm
5.8 ± 0.05 mm
5.6 ± 0.05 mm
5.4 ± 0.05 mm
5.2 ± 0.05 mm
5.0 ± 0.05 mm
5.0 ± 0.05 mm
Optical Radius Definition: See Optical Chart

 


Optical Design Studies


“O&Omdc” IOL-Moulds are designed for producing lenses from 3 to 33 dioptres in 0.5 dioptre steps and from 34 to 40 diopters by one diopter. The posterior surface should be machined spherical with different radius for each power. Other powers can be manufactured on special order.

“O&Omdc” IOL-Moulds power range will be divided into various preset front radius. Within each preset front radius, the anterior surface will be constant but may be spherical, aspherical or multi-zonal. At the maximum power in each zone the IOL should be equi-convex.


About Spherical Optics:


As IOL power increases, the shape of spherically surfaced IOLs has an increasing influence on performance. It is well known that the optimum IOL optical shape is close to convex-plano where primary coma is approximately corrected. The constraint that the IOL with highest power within each range should be equi-convex severely increases the sensitivity of the IOL to tilt because coma is significantly non-zero. However, there is another great consideration, related to constant ACD that affects the number of the preset front radius...

The maximum number of preset front radius of the “O&Omdc” IOL-Moulds is eight and this restricts the difference in power between the front and rear surfaces of the IOL to be 4 dioptres.

When the IOL has an equi-convex shape, the mid-point of the edge of the IOL and the mid-point between the two principle planes are coincident. This will occur at the highest power of each zone. As IOL power decreases within the zone, these two mid-points will separate. The ACD strictly refers to the mid-point between the two principle planes but during design the lens has been placed so that the mid-point of the edge is at the specified ACD.

When Df < 20 and Db < 20 the mid-point separation is, to a good approximation, given by the formula:

O&O IOL-Moulded Blanks

Where:

P is the dioptric power of the IOL,
Df and Db  are the dioptric powers of the anterior and posterior surfaces,
Ф is the optical diameter,
e is the edge thickness,
nIOL is the refractive index of the IOL material and
naq is the refractive index of the medium surrounding the IOL.


The dioptric powers are Df = 1000. (nIOL-naq)/Rf  and Db= 1000.(naq-nIOL)/Rb where Rf and Rbare the radii of curvature of the anterior and posterior surfaces in mm.

The mid-point separation is proportional to the difference of anterior and posterior dioptric powers. At high powers the first term inside the square bracket is dominant. At low powers the two terms have similar magnitude.

If the shape is equi-convex then Df  =Db and the mid-point separation is zero. If (Df  -Db) = 4 dioptres.

This is near to the acceptable limit i.e. that the maximum difference in power between posterior and anterior surfaces should not exceed 4 dioptres. The increase in mid-point separation at lower powers is compensated by the longer eyeball length that reduces sensitivity to IOL location.

The spherical power range has been split into 6 preset front radiuses. The two smaller front radius steps at low power have been chosen to minimize the dioptre difference between the two surfaces and two avoid the posterior surface becoming too shallow – or even concave. The maximum posterior to anterior surface radius ratio is approximately 2:1. The maximum spherical power of an IOL has been limited to 28.5 diopters.

The highest power IOL within each preset front radius has an equi-convex shape. The other IOLs within the preset front radius have the same spherical anterior surface and the posterior surface radius is chosen to give exactly the power required for the specified edge thickness and optical diameter.

In our optical studies, the refractive indexes have been set according to the measured values given by the raw material datasheet. The index used is nIOL at wavelength 546.1 nm and temperature 35°C as stipulated in the ISO 11979 for the “In Situ” condition. .


About Aspherical Optics:


An aspheric anterior surface option has been generated for the each of six highest power front radius steps.

Aspheric anterior surfaces have been generated for each IOLpolymer material. They are all optimised to have a ‘soft’ performance i.e. the third order spherical aberration is not fully corrected and is designed to match the spherical aberration in the emmetropic young eye. The residual third order spherical wavefront aberration is 0.5 wavelengths over a 3 mm diameter pupil.

The aspheric is a conic section. This gives a good match to the aberration of the emmetropic eye over a 4 mm diameter pupil but slightly decline at larger pupil diameter. A somewhat better match could be gained by using 4th, 6th and 8th power figuring coefficients but the gain is so small since the eye’s performance is already quite poor at these diameters and it is difficult to find reliable data for the higher order aberrations of the emmetropic eye.

The optical chart specifies just one anterior surface that is used with every lens in the preset front radius. It was best to make the aspheric optimum for the lens in the front radius that has the highest power. However, the advantage of the aspheric is progressively less for the lower power IOLs in the same front radius step. The merit function can actually be very similar to that of the spherically surfaced option at the lowest powers i.e. the aspheric is not having much effect. Therefore there is no interest to provide aspherical surface to a lens below 11.0 D.


Looking at the Multi-Zonal Optics called “Four-Leaf Clover”:


The “four-leaf clover” of the multi-zone surface are concentric and the four zones has the same power.
The “four-leaf clover” multifocal is “Trade Marks and Designs” protected in the whole European Community under registration N°: 001990524.
The registered “Trade Marks and Designs” certificate is shown below:

registered "Trade Marks and Designs" certificate

The power difference between the power of the zones and the nominal IOL power is 3.75 dioptre.

The specified power of the zones has been interpreted as the power that the IOL would have if the single zone covered the entire anterior surface as calculated according to ISO 11979-2, Annex A.

zone covered


The aspheric is a conic section. This gives a good match to the aberration of the emmetropic eye over a 4 mm diameter pupil but slightly decline at larger pupil diameter.

Far Vision acuity:
Far Vision acuity
Retinal image:
A=100, acuity chart is at 6.1 m.
Close Vision acuity:
Close Vision acuity
Retinal image:
A=100, acuity chart is at 400 mm.


The aberrations of figured aspheric surfaces are more easily controlled and this type of aspheric has been used to provide good aberration correction.

The outermost (nominal power) zone is designed first and is optimised to have zero spherical aberration when in situ with an infinite front conjugate.

The optimisation conditions are as follows.

  • The cornea is modelled as a 0.5 mm thick layer with refractive index 1.376. The anterior surface is modelled as a 16 mm radius, hyperbolic profile surface with a conic constant. The posterior corneal surface is modelled as a 17 mm radius spherical surface.
  • The in situ refractive index of the aqueous humour is assumed to be 1.336.
  • The in situ refractive index of the vitreous humour is assumed to be 1.336.
  • The zone power is maintained at the nominal IOL power.
  • The back focal distance is fixed at the in situ paraxial back focal distance.
  • The edge thickness is maintained at the specified value.
  • The lens is positioned with the centre-point of the edge at the specified ACD.
  • The spherical aberration is optimised to zero.

When the design of the outer zone is complete then each smaller zone is designed in turn. These zones have higher power and are designed to focus a target at a finite distance of 400 mm onto the retina at the same focus as the outermost zone with zero spherical aberration. The zones are positioned so that its profile is tangential to the inner circle of 1.3 mm. The outer diameter is 3.5 mm and is linked to the outer optical surface by a tool radius of 20 µm. This ensures that the surface can be machined and that the multi-zone profile is smooth. The optimisation conditions are as follows.

  • Cornea, aqueous humour and vitreous humour modelled as above.
  • Zone power maintained at the sum of nominal power and differential zone power.
  • Back focal distance fixed at the same in situ value as the outermost zone.
  • Target at the paraxial conjugate distance in air.
  • The spherical aberration is optimised to zero.

The resulting design is of the aspheric type. That is, the spherical aberration is corrected to zero. The multi-zone lens has not been designed to take account of the effects of IOL decenter and/or tilt. The only useful parameter that can reduce sensitivity to decenter or tilt is the lens shape and this is effectively fixed because the posterior IOL radius has been frozen during the earlier design of spherical and aspheric IOLs.

Conclusion:


“O&Omdc” has worked to further R&D into the advancement of new IOL Polymers using Half-Moulded System for IOLs. The “O&Omdc” is pleased to offer a wide range of Optical Mould Solution complying our customers’ needs and expectations.
“O&Omdc” IOL Moulds are fully compatible with both Hydrophobic and Hydrophilic Polymers, which are offered in various colours, from Clear Natural Yellow to Blue Filter, in order to satisfy the wider Ophthalmic market demand.
Moreover, thanks to constant R&D activities and assiduous market analysis, our customers have now the opportunity to take advantage of “O&Omdc” IOL Mould Technology which, thanks to its Half-Moulded Blank form, allows a cost reduction and an easy adjustment of the dioptric power.
The strength of this innovative technology is the automation of production that ensures a reduction of IOL manufacturing time and costs, in order to reach more efficient performances.


For any queries or comments, please contact:

Patrick MEUNIER, Email: p.meunier@oo-mdc.com


Thank you for choosing the "O&O mdc" IOL Polymers.