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Toric implant

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.

toric implant and refracted light

A toric implant (ex: o-ring EnVista) has a variable curvature: it generates astigmatism! Of course, at the insertion of the implant in the eye, this astigmatism neutralizes one of the cornea. The least powerful meridian of the implant (in blue) should be aligned with the stronger meridian of the cornea.

The toric implant compensates astigmatism induced by corneal.

toric implant for corneal astigmatism correction

The toric implant should be aligned with the cornea to ensure an optimal correction of astigmatism. The implant is equipped with small cues that allow are good positioning per operation. The couple 'cornea + implant' generates more astigmatism.

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.

toric implant map topographic anatomical landmarks

Topographical map of axial curvature: it allows to identify the axis of astigmatism (box) k and the superposition of the map with the "raw" image of the eye often allows to use anatomical landmarks like the conjunctival vessels to identify correctly the azimuth of a given Meridian.


Various software programs can be used to calculate the power of the ring implant, they are available online.

Astigmatism corneal ring implant calculation

Corneal astigmatism. Corneal topography (left) objective the presence of a generator corneal toricite of a refractive cylinder (astigmatism) of 3 dioptres. The toric implant (right) calculation of corneal astigmatism, the site and the size of the incision.  The power of "cylinder" of the implant (astigmatism what it fixes) is in general greater than the power of corneal astigmatism, because the implant is not located in the same plane as the cornea.

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).

marking axis ring implant

The marking of horizontality is done on the cornea with a marker to bubble (when the bubble is centered in the cylinder, horizontality is guaranteed!). Identification of axis 0 ° - 180 ° is done while the patient is seated and look straight ahead. It allows to avoid a "misalignment" which could be related to a slight rotation of the eyeball while lying (during the procedure).

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.

astigmatism axis tracking

A ring graduated in degree is made using previously worked horizontality marks (a). The axis of the arched Meridian is then marked on the cornea (b). That's according to this axis that the implant will be aligned (the optics of the implant is provided with marks next to its lowest Meridian).

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.

toric implant AT Torbi

AT TORBI toric implant for correctionde astigmatism in cataract surgery. The implant should be aligned next to the axis Meridian (12).


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.

callisto system

Callisto (Zeiss) system for cataract with o-ring implantation surgery. Here the lines materialize the axis (12). The markings on the implant to align it on the route of these lines.

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 °:

alignment implant, callisto

Alignment of the implant along the image projected by the by augmented reality (Callisto, Zeiss) surgical assistance system virtually.

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.

toric implant OPD SCAN III toric IOL display

Topography and OPD after insertion of a toric implant (previous example where the axis of alignment was to be 12 °). The agreement between the axis of the arched Meridian (in red) and the implant is perfect. Residual astigmatism is less than 0.5 D (while he was in preoperative 5 d).

When the implant has an optimal alignment, the neutralization of corneal astigmatism is maximum.

Topo OPD toric implant

The topo aberrometrique (OPD SCAN 2, Nidek) survey was conducted after cataract surgery and a toric implant insertion. Note the perfect harmony between the axis of astigmatism caused by the cornea (lower-left) and that generated by the o-ring (lower right) implant. These astigmatismes 'neutralize' and the operated eye is thus cleared of total astigmatism (top-right)

In case of misalignment, a rotation of toric implant may be considered secondarily.

15 responses to "o-ring implant"

  1. Dr. Damien Gatinel says:

    If you have a cataract, s present commonness of the Visual symptoms in connection with: sailing, glare, dull colors... the operation is therefore necessary initially. A toric implant placement is recommended in case of astigmatism to perfect your distance vision. It is important that you discuss with your surgeon the possibility to leave a slight residual myopia in order to be able to read without glasses. By far, a low myopia causes a blur light but much less than occaseionne your strong myopia and glasses can be ocaseionnel (driving etc). You should take satisfaction of the intervention with the benefits brought by the removal of cataract and the significant correction your myopia and your astigmatism.

  2. BOIREAU says:

    I had cataract surgery on the 1 12 15 with an O-ring. (Near Vision)
    When checking the doctor tells me that I lost 0.25 in myopia ie – 3.25 instead of – 3

    How is this possible

    with my thanks

    Michele BOIREAU

  3. Dr. Damien Gatinel says:

    This difference is minimal, and is even less than the precision (+/-0.50D) that has the right to wait for the refraction of the eye after cataract surgery and put a toric implant. She has no real impact on vision in postoperative.

  4. Dr. Damien Gatinel says:

    The secondary rotation of a toric implant is a gesture that is indicated when the axis of the implant is not aligned avecla direction of astigmatism (sometimes the implant "turn" after its installation). This gesture is quite small and low-risk. It is not mandatory, and as you point out simple glasses are also effective to correct residual astigmatism. Nevertheless it seems relevant to reposition the implant is proposed by your surgeon. This will be done under simple local anaesthetic by drops most likely.

  5. Annette says:

    I had laying d implant ring Monday on the 2nd eye (the 1st eye was done 3 weeks ago and is well fixed in close-up).
    But this time 3 days after the implant pose for the 2nd eye with correction from afar.. I see very blurry beyond 8 to 10 metres...et especially I see much less than before...
    What do you think?

  6. Dr. Damien Gatinel says:

    It is difficult to answer your question accurately. If the vision is clear up to 8-10 meters, it is already a very respectable performance. Your mixed impression is can be linked to the persistence of a corneal astigmatism, insufficiently corrected by the ring the second eye implant. It should be above all to make the point with your surgeon.

  7. SANTA Renée says:

    I was operated in the left eye may 2, 2016 and the right eye on May 23. I had to ring implant in both eyes. I see very well in the right eye, but I have a problem with the left, I like a shadow in the corner of the eye, and sometimes I see blurry. Could you tell me if this is normal and if over time it will disappear. Thank you for your response.

  8. Dr. Damien Gatinel says:

    This is may be what is called a "dysphotopic", more information here

  9. kiezer says:

    Operation Cataracte August 4, 2016
    Soft O-Ring
    Nevertheless since this intervention night vision (streetlight, car headlights) are distorted by a very defined prism. By unimportant brightness, unpleasant halos.
    The surgeon tells me very terse that it comes from the implant without further explanation.
    What about it?
    Thank you for your answer

  10. Dr. Damien Gatinel says:

    Necessary for a detailed examination, including a measure of aberrometrique (eye Wavefront), as well as a review of the implant after dilation of the pupil. A big scratch on the implant, or the folds of the cristallinienne capsule (capsular bag) may cause irregular light spreading, bright lights all about streaks, etc.

  11. kiezer says:

    Thank you doctor for your answer
    Nevertheless, let me ask you whether this anomaly can be corrected and how?
    Can the correction bezel port be a solution
    Thank you for your answer

  12. John J says:

    Hello doctor

    I wanted to know if this implant can be beneficial for a moderately advanced pilucide degeneration with a large astigmatism,

    Thank you.

  13. Dr. Damien Gatinel says:

    The installation of an O-ring is quite possible as part of the cataract surgery for an eye with pellucida degeneration. In this condition, astigmatism is of corneal origin and generally very pronounced.

  14. HERMAN says:

    Hello Dr GATINEL,
    I beg your help. Mr L. carries a bilateral Keratoconus and has undergone a corneal transplant in the years 90 on his OD, it is the eye that interests us. The graft is slightly off-center. Its Topo shows a strong astigmatism with a "semblance" of regularity (cornea very curved but coarse shape in hourglass).
    kerd: 49.63 40 °, 59.11 130 ° (-9.48) 40 °/
    It is about the cataract on this side. This patient is also strong nearsighted which would require the installation of a negative implant. What do you think of the opportunity to implant a negative and toroidal PKI? If you find the indicated toroidal implant, do you think it is necessary to correct all of its corneal astigmatism?
    Thank you for taking the time to read me.

  15. Dr. Damien Gatinel says:

    In this context, it seems a priori advisable to use an o-ring to correct the corneal astigmatism. It is fairly preferable to be rather under than on corrector, but if astigmatism is proven, then it requires an equivalent power for its correction in the plane of the implant of Crystalline lens Artificial. The difficulty is to estimate the effect of the posterior side of the graft: if it is "parallel" to the posterior side, then its astigmatism is "compensator" for some of the astigmatism of the anterior side. A precise estimate is quite difficult however.

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