Eyeworld

The ocular surface: The first refractive interface of the eye 4 by Edward Holland, MD Impact of ocular surface disease on topography, aberrometry, and astigmatism correction decisions Improved OSD diagnosis and management can lead to better postoperative outcomes O cular surface disease (OSD) can significantly impact many aspects of refractive and cataract surgery, including pre- operative measurements, surgical planning, and intraocular lens (IOL) selection. However, OSD is often undiagnosed and under- treated. 1 By improving detection and treatment of OSD, surgeons can obtain more accurate preoperative measurements and achieve better outcomes. Impact on measurements Before cataract surgery, OSD may significantly affect keratometry, A-scan, and topography measure- ments, affect the selected IOL Practice pearl: Even if a patient does not have true astigmatism, we may see astigmatism created by dry eye, resulting from aqueous tear deficiency or meibo- mian gland dysfunction. Therefore, astigmatism may be mismanaged based on an erroneous keratometry or to- pography reading. Likewise, we may choose an incorrect spherical power. –Edward Holland, MD power and astigmatism manage- ment, and determine whether a presbyopic IOL is suitable for a specific patient. Even if a patient does not have true corneal astigmatism, a false recording of astigmatism may occur due to dry eye from aqueous tear deficiency and/or meibomian gland dysfunction. Therefore, astigmatism may be mismanaged based on an errone- ous keratometry or topography reading. One of the more common complaints of patients with OSD is vision fluctuation, which often results from evaporative dry eye caused by meibomian gland dysfunction. Patients with a sig- nificant cataract may not notice the fluctuation preoperatively. If a clinician fails to diagnose OSD, the patient's quality of vision will be reduced significantly and the patient will blame the dry eye associated fluctuation in vision on the IOL or inadequate surgery. This situation is exacerbated by the multifocal lens. Therefore, it is essential to recognize dry eye and treat these patients preoperatively, especially if considering a premium IOL. Red flags The diagnosis of dry eye can often be made prior to the patient being examined by the surgeon. Technicians should be trained to understand the findings of dry eye on the preoperative testing and alert the clinician when IOL calculations may be abnormal because of OSD. On standard ker- atometry, this may result in irreg- ular mires. On topography, OSD may result in areas of steepening or flattening within the readings that are not respective of a single meridian. Dry eye can result in inferior steepening mimicking forme fruste keratoconus. In a cross-sectional study of 100 symptomatic dry eye subjects and 35 normal subjects, Cui et al. assessed the corneal epithelial thickness in dry eye patients. The study reported patients with higher dry eye severity grades had thinner superior (p=0.017) and minimum (p<0.001) epithelial thickness. 2 Discrepancies in the various measurements, such as kerato- metric readings, biometry, and topography, commonly are a sign of OSD. If there is significant OSD with corneal staining with fluo- rescein or staining of the conjunc- tiva or corneal epithelium with lissamine green, it is advisable to aggressively manage the dry eye and potentially delay cataract surgery, especially if the patient plans to receive a premium IOL. Additionally, hyperosmolar- ity has been shown to affect the measurements of astigmatism and IOL power in that dry eye may cause physicians to overestimate corneal astigmatism and affect the management of astigma- tism. 2 However, if the dry eye is managed, one may find that the amount and location of the astig- matism may be significantly less, it may not be present, or it may be present at a different axis. Conversely, we may not de- tect astigmatism because the dry eye masks it. When we optimize the ocular surface we may see astigmatism. Patient selection If a patient has chosen a premium IOL—either a toric IOL or presby- opia-correcting IOL—and expects excellent visual outcomes but has corneal staining, we frequently delay surgery to manage the OSD and repeat testing so measure- ments will be more accurate. The patient will be frustrated with the dry eye diagnosis but not frustrat- ed with the surgeon. However, if OSD is detected but not treated before surgery, the patient will be dissatisfied with the visual outcome and often blame the surgeon, not the dry eye. We do not delay all surgery in patients with OSD. If we have a situation in which an elderly patient has clinical findings of dry eye and is eager for surgery, we will diagnose and treat the OSD, but we may elect not to delay surgery if he or she is receiving a monofocal IOL. However, even in this patient, aggressive treatment of the OSD will significantly im- prove the patient's vision. Postoperative correction OSD also impacts postoperative decisions. The most common rea- son to exchange an IOL is patient dissatisfaction with a multifocal IOL or if astigmatism was under- or overcorrected. Visual outcomes from multifocal IOLs are very dependent on an excellent ocular surface. In the vast majority of cases, dissatisfied multifocal IOL patients who are referred to me are unhappy because of OSD. Overwhelmingly, if we optimize the ocular surface, most patients will be pleased with their vision and the IOL will not need to be exchanged. " Visual outcomes from multifocal IOLs are very dependent on an excellent ocular surface. " –Edward Holland, MD continued on page 6

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