Giving due consideration to preoperative marking and the surgical technique in toric IOL implantation, as well as being diligent about reviewing postoperative results, can improve patient outcomes whilst minimising the chance of errors.
This three-part series on using toric IOLs in cataract surgery is designed to provide some practical tips for success. Part 1, published in the October edition of Ophthalmology Times Europe®, looked at patient selection and optimising biometry. Part 2, published in the November issue, covered the calculation of toric IOL sphere and cylinder power. In this final article in the series, I will examine the perioperative period and provide postoperative troubleshooting.
A toric IOL has maximum optical impact when aligned perfectly with the steep axis of the cornea. If it is a few degrees off, there is a decline in effect of astigmatic neutralisation. In general, most surgeons consider alignment within 10° to be accurate enough but in reality, a lot depends on the magnitude of astigmatism.
Misalignment of a high-power toric IOL can leave someone with a lot of residual astigmatism whereas misalignment of a very low cylinder power toric IOL may have a minimal effect. To align a toric IOL accurately, a reference mark must be used. There are many different methods of preoperative marking: ink markers, needle marking and even apps.
I prefer to use an intraoperative digital display system (Verion Digital Marker, Alcon or Callisto Eye, Carl Zeiss), not because these methods are more precise than manual marking but because they are more efficient and speed up the surgery. I do still make a manual mark on the eye in the sitting position prior to surgery as a back-up reference in case of difficulty with the digital system, but rarely need it.
Regarding manual marking, a single mark is adequate to align a Mendez ring. The human eye is incredibly good at halving things, so I will make a small mark inferiorly at the bottom of the cornea to split the cornea in half.
In the worst-case scenario, if your digital marking system fails, you have not pre-marked the eye and you still want to implant a toric IOL, I suggest that you still can safely do so. Simply look at the top of the cornea and identify the vascularised pannus. If you look at the midpoint of that pannus, this will be the midpoint vertically and you could drop a line down from that to halve the cornea.
If you look again at the widest point of the cornea and draw a line horizontally across it, you are going to give yourself an excellent surrogate marker; you could then use a Mendez ring and still be able to mark the axis to implant the toric IOL. You can safely use a toric even in this worst-case scenario.
The surgical technique of toric IOL implantation differs from standard cataract surgery because of the preoperative marking and the rotational placement of the lens. The IOL injection is similar to cataract surgery but I recommend being primed and ready to rotate quite rapidly as the IOL is expanding.
The unfolding of the IOL is a prime time to get it into a good position. Many will suggest, if you are using a C-loop haptic, to put it 5° before where you want it so that you can nudge it into the final resting position when you are doing the next steps of surgery. If you are using a plate haptic IOL, you can put it exactly where you want it because you can nudge it in either direction very easily.
I do not use a capsular tension ring unless necessary due to zonular instability, even in high myopes. I find that toric lenses from the major manufacturers have good rotational stability, and the need to rotate is extremely low.
If you do find that you have over-rotated your toric IOL past its intended position, there is no shame in turning it around again. Take your time. Inject some more viscoelastic into the capsular bag and use two instruments to completely rotate the lens all the way back to where you want it.
If you are wanting to move just a few degrees in the opposite direction, it is possible but be wary of putting too much stress on the capsule. My tip is to slightly deflate the anterior chamber, which will allow easier “backwards” rotation of the IOL within the capsular bag.
A key time that you may encounter a little IOL rotation away from its intended position will be at the end of the case when you take the instruments out of the eye. Sometimes, if the incision has not perfectly sealed, shallowing of the anterior chamber will allow some movement of the toric IOL within the capsule.
I highly recommend being quick with your incision hydration, trying not to let the anterior chamber flatten and keeping things quite firm at the end of the case. This prevents setting up a cycle of IOL rotation, entering the eye, flattening the chamber and further movement, etc. I have noticed a major decrease in my need to hydrate the main incision after injecting the Clareon toric IOL with the AutonoMe injector and this has been helpful in leaving a stable anterior chamber at the conclusion of the case with little risk of early rotation.
If you notice any early rotation after you have finished the case, go back in and put the lens back where it needs to be. This is a lot easier to do while you are still in the operating theatre rather than seeing it the next day and wishing you had taken the extra few minutes.
Postoperative care of a toric IOL patient is identical to that following any other cataract surgery. I recommend seeing the patient at 1 day, 1 week and 6 weeks postoperatively. On Day 1, I start to look for any early and significant rotation. If I notice a lens with significant malrotation, I take the patient directly back to the operating theatre and put the lens in the originally intended position.
If I notice on Day 1 that the lens is off by a few degrees, I am not concerned because the patient may be completely happy and it is fine to wait and see. Also, if the lens has moved a little, it means that it is not particularly stuck to the capsule and is a somewhat mobile. I would rather wait for the capsule to become more condensed so that if I do choose to rotate the lens, it is more likely to stay in that position long term.
At the 6-week postoperative appointment, I audit my results, looking at lens position both in terms of axial position and depth within the eye. This is also when I would perform an accurate subjective refraction.
Even if the patient is happy, I recommend doing a subjective refraction. It will give you so much more information that you can use to improve your future results. I also take more optical biometry measurements for my records. These are handy if I want to consider any kind of toric rotation or lens exchange and provide me with postoperative anterior chamber depth.
If a patient has significant post-op astigmatic refractive error, I follow a structured decision-making tree by asking myself first whether the patient is happy. If the patient is unhappy, I want to do something for them. On the other hand, a happy patient with refractive error may be truly happy as they are or may prefer glasses anyway so do not try to fix things — instead, learn from what may have gone wrong in that case.
If you examine the patient and find the lens is exactly where you intended yet they still have some residual refractive error, you may ask yourself what you have done wrong, but the answer is likely nothing. Either the patient had significant change in their surgically induced astigmatism or their initial biometry was not quite right. This is now a situation that needs a little further investigation before treatment decisions can be made.
You simply need a subjective refraction and measurement of the axis and pseudophakic anterior chamber depth, along with knowledge of the sphere and cylinder power of the implanted toric IOL. Working out whether you can rotate the IOL to fix the residual astigmatism or if an IOL exchange may be needed can seem daunting.
You will need to use an online tool to help you with this, but a good rule of thumb is that if the spherical equivalent of the subjective refraction is close to zero then you should be able to rotate the current IOL into a more optimal position for the patient. Ultimately, the patient will have to decide whether they want to have another surgical procedure so that you can rotate the IOL or whether they can have laser treatment to the cornea.
My preference is to rotate the lens to a better position to get rid of the residual astigmatism if I can, and it is a simple solution. My colleague Dr Michael Goggin and I created an app called Toric Pro.1 Other calculators include astigmatismfix.com and the Barrett RX formula. All these resources can tell you whether you can rotate the lens for a better residual refractive outcome.
There will be some patients who do not want to undergo surgery again and there will be some eyes that you will not want to re-enter. Perhaps they had unstable zonules or it was a difficult operation. For these cases, laser vision correction can be a safe and effective option.
Again, the most important thing in this situation is an accurate subjective refraction as this is what will be used in planning the laser surgery. Most people will know a friendly laser surgeon who is happy to help with such cases.
One of the most important points to make about re-rotating an incorrectly positioned IOL is that it is not appropriate to simply put the IOL at the originally intended position if it is not there already. Once you have made an incision and implanted a toric IOL, you have changed the eye. Surgically induced astigmatism has altered the shape and you now know how deep the toric IOL sits.
You have new information and a new subjective refraction to work with. Do not be tempted to just go in and put the IOL back unless on Day 1 there is a large rotational change from intended. In this scenario, I think it is reasonable to go back and reposition, often with the added security of a capsular tension ring.
If at any stage you do have to go back inside the eye, it can be particularly stressful because you want to get it right this time and because this is not a common procedure. My suggestion, if going back into the eye early, is to free up the lens and take a minimalist approach.
Use a little viscoelastic but do not fill the bag. Rotate the lens to its new position — and I always gently press or tap the IOL against the capsule to maximise contact between optic material and capsule.
If going back into the eye much later, when capsular fibrosis has sandwiched the IOL in place, take your time and be kind to the zonules. I recommend putting a needle between the IOL and the capsule edge before visco-dissecting the two apart.
There are times when an IOL simply cannot be completely removed and haptics must be left inside the bag. It is always good to have a sulcus and anterior chamber IOL option on standby in case there are any complications with this relatively tricky procedure. Also, remember that if you find yourself having difficulty rotating a previously implanted toric IOL, there is no harm in backing out and deciding that the safest course of action is to instead perform laser vision correction surgery.
I would like to encourage surgeons to implant toric IOLs more frequently. The tips and advice I have given in this series of three articles will help you plan for success and to be prepared for the rare occasions you must deal with failure.
Success is all about doing all the small steps well and minimising the chance of error. You will have to be a little more pedantic about reviewing preoperative results and considering postoperative data but the improvement in patient results will be worth it.