Refracting Refractive Surgery Patients

Since its first appearance, numerous, important advances have been achieved in the field of Refractive Surgery: technological, medical and optometric. Nevertheless, the success of the procedure invariably depends on an appropriate pre-operative ocular examination in order to assess both the suitability of the candidate for the surgery and to measure the parameters needed for the surgical plan. The importance of accurate refraction cannot be overemphasised for those patients contemplating Refractive Surgery of any kind. There are many reasons for this, not least the fact that the success of the surgery is most frequently judged on the final mean spherical equivalent of the patient post-operation, and clinical audits depend entirely on accurate information. In the post-operational period, it is also used in order to evaluate the healing process, possible regression of ametropia, and any enhancements that need to be considered to improve the final result. The pre-operative evaluation serves both to assess the suitability of the candidate and for surgery planning. Refraction here plays a major role, first identifying the condition in order to choose the most appropriate surgical technique, and second to quantify the amount of correction needed, when ocular refraction results are combined with the rest of the ocular parameters measured. The awareness of the importance of accurate refraction can be seen in the common pre-consultation advice that is given to patients. It is well accepted that contact lens wearers should be are asked to remove their contact lenses several weeks prior to their pre-operative consultation, to ensure that any corneal distortion that could change the refraction is eliminated. Also, patients are often asked to produce past refractive details for up to the past three years to show that they have retained a level of stability. If the patient had a recent change in their refraction then they may be asked to wait until their prescription has stabilised. With pregnancy, a period of at least three months post-partum should be left before the assessment of the refractive status for Refractive Surgery, since the hormonal changes occurring during pregnancy may significantly alter the refraction. If a patient were to have Refractive Surgery and then find that their prescription has had a natural myopic or hyperopic change, they may unsurprisingly feel wrongly disappointed with the results of the surgery. The patient’s acuity is normally recorded in Snellen format. However, it has been suggested that recording the logMAR acuity would be more relevant especially if any analysis is to be completed on the results. The Bailey Lovie charts use letters of approximately equal legibility, where there is the same number of letters for each size level, and the spacing between letters and the rows is a constant proportion of the letter size. These charts are available in both high and low contrast and the geometrical size progression leads to a better scoring method. One of the most important reasons why refraction preoperatively needs to be accurate is that the treatment plan will differ depending on the refraction of the patient. A proposed treatment plan is shown in Figure 1. The level of myopia or hypermetropia will strongly dominate the surgery process with the patient needing to be counselled as appropriate. For example, many patients do feel that their level of myopia is worse than it really is. It is fundamental that an accurate prescription is measured for all probable patients as it can be difficult to tell from history and symptoms those patients with an inaccurately corrected refractive error. A patient whose current prescription is too minus will end up over corrected and therefore hyperopic. The patient that has an undetected latent hyperopia will end up under corrected and therefore still hyperopic. It is for this reason that cycloplegic refraction is recommended before refractive surgical treatment. Cyclopentolate is the most commonly used drug for blocking the responses of the sphincter muscle of the iris and accommodative muscle of the ciliary body to cholinergic stimulation resulting in mydriasis and cycloplegia. The results obtained in cycloplegic refraction should be then compared to manifest refraction, normally using fogging with plus lenses, in order to better estimate the correction required. When dealing with hyperopic patients in whom manifest and cycloplegic refractions differ by more than 0.5D, the correction would then move towards the cycloplegic refraction values. This will result in any latent hyperopia being picked up which will allow the surgeon to fully correct the prescription. The binocularity of a patient must also be considered before the cycloplegic is instilled and prior to the surgery plan being decided. It is important to note that correcting the refractive error might cause a binocular problem, which was previously balanced with the normal prescription. Normally, situations such as a highly exophoric patient with hyperopia would be known previously from the optometric history. However, it is always useful to ensure that these secondary complications, easily avoidable, do not appear. An example of this would be if a patient who is +3.00DS R & L with an 8∆ exophoria. If they wear a +2.50DS correction in spectacles this makes them accommodate, so helping to control the phoria. Full surgical correction will remove this option. In most cases amblyopia is considered a contraindication for any type of Corneal Surgery, but sometimes the difficulties are more subtle. It is also necessary to counsel non-contact lens patients with a high myopic prescription that they may have some discomfort in reading for long periods of time after having Refractive Surgery. Theoretically, the accommodation and vergence demands are different between single vision contact lenses and spectacle lenses. Myopes are required to exert more accommodation and vergence after Refractive Surgery (or Refracting Refractive Surgery Patients