EyeWorld Asia-Pacific March 2020 Issue

EWAP MARCH 2020 3 EDITORIAL Graham Barrett Chief Medical Editor EyeWorld Asia-Pacific O ne of my most enjoyable tasks is providing an editorial for our EyeWorld Asia-Pacific news journal. Frequently, selecting a topic is straightforward but the current issue is like a treasure chest containing many jewels and pearls relating to intraocular lenses that are worthy of comment. The articles on the expanding range of presbyopia treatments, corneal incisions, and better capsulotomies are invaluable, but the article that to my mind demands particular focus relates to the challenge of cataract surgery in patients with preexisting keratoconus, particularly in relation to selecting an appropriate IOL. Lens selection is challenging in determining both the spherical and the astigmatic outcome. Most of us who have experience of patients with keratoconus have determined that unexpected hyperopic outcomes are not uncommon. Targeting a refractive outcome of approximately –0.75 D can help avoid an unexpected hyperopic surprise. Nevertheless, this can be challenging as there is no clear demarcation between the patient with an irregular steep cornea with forme fruste keratoconus and one with evident clinical keratoconus. In the former situation, the predicted outcome does not require adjustment; this is not the case with fully established keratoconus. The problem relates to the altered relationship between the posterior and anterior cornea as well as the displaced corneal apex and uncertainty as to what region of the cornea the patient is using for vision. I suspect this is one situation where measuring the posterior cornea with swept- source Scheimpflug devices may indeed be helpful in improving the spherical outcome prediction in patients with keratoconus. Perhaps even more challenging is the decision whether to utilize a toric lens in these patients. Many patients with keratoconus do have a record of reasonably corrected acuity in the range of 6/9 with correction in their historical record. If this is the case and an axis can be identified then I would suggest that a toric implant would be worthwhile, particularly if the patient is not accustomed to wearing a rigid contact lens. Although the outcome is not as certain, one could expect a significant reduction in the amount of astigmatism to a level where spectacle correction becomes acceptable. The high level of astigmatism in these circumstances may require a toric cylinder beyond the standard range but custom higher cylinder toric lenses can be ordered from certain manufacturers. It is also worth scrutinizing the topography carefully as this may demonstrate a lower level of astigmatism in the central cornea than the more peripheral cornea and there may be considerable variation in the K’s, compared to those obtained from standard biometers. This is one circumstance where I would recommend looking at the patient’s spectacle correction prior to developing cataract and taking this into account in selecting the required cylinder power. In contrast, if a patient is accustomed to wearing RGP contact lenses and has never obtained satisfactory vision with spectacles, then it would be best not to perform a toric lens. Although custom toric RGP lenses can be obtained in theory this is more complex and may not be achievable. As we improve our ability to predict outcomes in normal eyes regardless of axial length and in eyes that have undergone previous refractive surgery, I believe we need renewed focus on patients who have preexisting keratoconus and require cataract surgery. EWAP