Patients with keratoconus, like all patients, eventually develop cataracts. However, cataract surgery in these keratocomic eyes is not the same and there are special considerations and techniques that can help ensure a good outcome for these patients.
Usually these patients are age 60 or more and the keratoconus progression has stabilized. These patients tend to wear hard contact lenses which help give a more stable corneal contour and refractive surface. In all likelihood, if we are just doing a cataract surgery and no corneal procedures, these patients will go back to wearing similar contact lenses after cataract surgery.
We want to implant a monofocal IOL and avoid using multifocal IOLs. We should also avoid toric IOLs in most cases because the regular, symmetric astigmatic profile of the toric IOL is not well-suited to the irregular, asymmetric profile of the cornea. Also if the patient returns to a hard contact lens which will neutralize much of the corneal astigmatism, then the astigmatic effect of the toric IOL will be unmasked and will need to be addressed.
For the IOL calculations, the difficulty is measuring the central corneal power. Take measurements from all available technologies: auto-keratometry, optical coherence biometers, topography, and dual scheimpflug tomography.
Choose the lowest K values from these machines for the IOL calculations so that the subsequent variability falls in the myopic range for post-op refraction. Also aim for some residual myopia, such as -2 or -3 spherical equivalent to ensure at least a mildly myopic outcome.
During cataract surgery make the incision at the thicker parts of the cornea, with care taken to avoid the thinned out cornea. The view through the cornea during the cataract surgery will also be somewhat distorted and care must be taken to avoid iatrogenic damage to delicate intra-ocular structures. At the end of the procedure, make sure that the incision seals well and if there is any leak, place a 10-0 nylon suture to secure the wound.
click below to see the full narrated video of cataract surgery in keratoconus:
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From Santhan Gopal via FaceBook:
In my experience of cataract in KC patients, the factors to be kept in mind are
1.The axial length. Some KC patients tend to have axial lengths longer than 25 mm and they behave like cataract in high myopes! Very soft globe with very low scleral rigidity sclera tends to collapse. Phaco settings have to be chosen with care.Low bottle height and low flow very much needed.Make a large capsular opening ( 6 mm like) as in the bag phaco may be very difficult due to very deep anterior chamber, and lack of vitreous support to the posterior capsule.At times you may have to do phaco , bringing the nucleus outside the bag. As soon as the phaco tip enters the anterior chamber, the AC deepens and you need to refocus the microscope! As Anterior chamber is deep, outside the bag phaco should not be a cause for concern.
2.The view can be affected, due to scarring, otherwise no problem.
3.All possible methods of assessing the IOL power should be employed. But all are likely to be different and vary widely. Take the other eye reading also, if it is normal or forme fruste state.
4.They will not have as good a vision ,post op as before the op! Warn the patients well in advance
5.Corneal power alters and so they need a different Rose K lenses post op, warn them about the delay in post op visual recovery.
These are some points that I have learnt over a period of time