Toric implant: definition
A toric implant allows to correct theastigmatism after cataract surgery. More than 40% of the operated eyes of cataract present a regular corneal astigmatism greater than 1 diopter. To improve Visual acuity by the eye surgery without glasses, it makes sense to consider the correction of astigmatism of the cornea by the insertion of a toric implant, designed to correct the astigmatism: toric implant actually generates an astigmatism in opposite direction to that of the cornea.: This allows to neutralize the entire eye astigmatism! The surgery of cataract with o-ring implant fits well as one of the modalities of the astigmatism surgery.
The toric implant compensates astigmatism induced by corneal.
O-rings implants are designed to correct astigmatism of corneal origin.
In case of corneal astigmatism pronounced (greater than or equal to 1.50 D), Visual acuity uncorrected after cataract surgery will be reduced; the port of corrective lenses to correct the astigmatism will be necessary to obtain a good distance vision. However, astigmatism correction is possible during the procedure: is at the level of the cornea (incisions relaxing to reduce corneal astigmatism "mechanically": incisions cause relaxation of the arched meridians), either through an "o-ring" said implant insertion This implant can correct astigmatism (it generates an astigmatism of magnitude opposite to that created by the cornea: these two astigmatismes neutralize).
Features related to the choice of a toric implant
During the preoperative consultation, information about corneal astigmatism of the eye to be operated is collected: distinction at this point astigmatism induced by internal astigmatism (corneal astigmatism pure) cornea (astigmatism associated with the lens; should not be considered for the calculation of the toric implant since the lens is removed during cataract surgery).
The appeal to the corneal topography is useful for analyzing more precisely the characteristics of corneal astigmatism. These maps allow also to well identify the axis of astigmatism orientation, and sometimes closer to some anatomical features that may be useful during surgery to align the implant according to the desired direction.
Various software programs can be used to calculate the power of the ring implant, they are available online.
Calculation of toric implant software delivers the power of the implant, the degree of astigmatism caused by o-ring implant, and the axis where it should be positioned. Respect for this orientation of the implant is crucial.
Toric implant: surgical technique
Align the o-ring implant, you must follow certain precautions: the marking of the axis where should be brought into line ' implant on the cornea before intervention is essential. We can, as said above, use the map of corneal topography, or a pendulum marker or 'a bubble' to identify the horizontal axis (which suppose to check that the patient's head is upright and not leaning to one side or the other).
Brands (O ° - 180 °) allow to identify the axis which must be positioned the toric implant. This axis is close or confused with the axis of the arched meridian of the cornea. L' optimal alignment of toric implant in the cristallinien bag, after removal of the cataract is a condition the effectiveness of corneal astigmatism correction.
Support per operative alignment: Callisto (Zeiss) system
This system is based on the use of recognition software of the images captured by the operating microscope. Identifying marks of horizontality is performed automatically. The lines are then added on the image of the eye seen by the surgeon. These lines are aligned with the axis which must be positioned the implant.
In the following example, the o-ring AT TORBI implant must be positioned on the shaft (12). It features 7 diopters of astigmatism correction in terms of the implant. Its power has been calculated 'online' (biometrics) after measurement of the axial length of the eye, the depth of the anterior Chamber, and measure k.
Marks (0 ° - 180 °) were performed while the patient was in a sitting position, just before the intervention. Those brands serve as markers for the Callisto software, which then displays the guide lines to allow to position the implant (it has brands that facilitate this alignment). At the end, the video assistance and augmented reality system (the image of the ideal axis appears in the eyepiece of the microscope) allows the surgeon to align the implant along that axis.
For example here is what sees the surgeon once posed the toric implant (here, implant o-ring EnVista, Bausch & Lomb): marks placed at the edge of the optics of the implant can identify the axis of the implant. It should be aligned with the axis of reference, dictated by the biometric calculation and custom made prior to the intervention (through a system of calculation online) - here this axis is 87 °:
Toric implant: postoperative control
A topographer aberrometer equipped with a function to view overprinting of corneal topography and the implant used to enjoy the alignment after surgery.
When the implant has an optimal alignment, the neutralization of corneal astigmatism is maximum.
In case of misalignment, a rotation of toric implant may be considered secondarily.