Outline

  • Purpose of Review
  • Recent Findings
  • Summary
  • Keywords
  • Introduction
  • Sources of Error
  • Prior Radial Keratotomy
  • Improving Accuracy
  • Practical Application
  • Guidance to the Physician
  • Managing Outcomes
  • The Future
  • Conclusion
  • References and Recommended Reading

رئوس مطالب

  • هدف بررسی
  • یافته‌های اخیر
  • چکیده
  • مقدمه
  • منابع خطا
  • کراتوتومی شعاعی قبلی
  • افزایش دقت
  • کاربرد عملی
  • راهنمای پزشکی
  • کنترل نتایج
  • آینده
  • نتیجه‌گیری

Abstract

Purpose of review Since its introduction in the 1980s, more than 40 million people worldwide have undergone some form of kerato-refractive surgery. Many of these individuals are now candidates for cataract surgery and pose the challenge of attaining first-rate refractive outcomes in non virgin eyes. Numerous approaches have been developed to estimate intraocular lens (IOL) power in eyes post refractive surgery. This review highlights the most practical, relevant options for accurate IOL power determination in these cases.

Recent findings With refined techniques and advances in instrumentation, more accurate assessments of true corneal power and thus, IOL power, are possible in post refractive eyes. Optical coherence tomography and other corneal tomography instruments have markedly improved accuracy in this process. However, when expensive, modern equipments are not readily available, and online IOL calculators such as the American Society of Cataract and Refractive Surgery (ASCRS) calculator have become efficient, reliable options. Recent evidence confirms the accuracy of these online calculators.

Summary Emerging literature supports the use of methods that do not rely on prior refractive data in IOL power determination. Online IOL calculators provide user-friendly, efficient options that greatly facilitate accurate IOL power determination for cataract surgery in eyes that have undergone prior kerato-refractive surgery.

Keywords: - - - -

Conclusions

There are a multitude of methods to aid in accurate calculation of IOL power for cataract surgery in eyes previously treated with kerato-refractive surgery. Mounting evidence points to accurate, predictable refractive outcomes when methods that do not require prior refractive data are utilized. Well established examples include the Shammas and Haigis-L methods, which do not rely on historical information, which may be inaccurate or unavailable. There are three major sources of error in IOL power calculation. The instrument error stems from an inability of most keratometers to directly measure central corneal power. Most keratometers assume a constant index of refraction (1.3375) between the anterior and posterior corneal surfaces. This leads to error, as this relationship may be altered post-LVC. Finally, IOL formula errors stem from an inaccurate estimate of the ELP in eyes post-LVC. The Shammas and Haigis-L methods avoid this error, as they do not use the corneal radius to predict the ELP. Several instruments are available for keratometry and biometry, but many require formulas to adjust for prior LVC. The IOLMaster is one of the widely used instruments for IOL power calculation and is relatively reliable. More advanced techniques utilizing OCT, slit-scanning tomography or Scheimpflug Based principles are likely to be more accurate in predicting refractive outcomes, as the posterior corneal curvature can be directly measured. However, these instruments are expensive and not readily available. The advent of online IOL calculators such as ASCRS and Ocular MD calculators has greatly facilitated reliable IOL power calculation in eyes post refractive surgery. Despite some level of inevitable uncertainty, especially in nonvirgin eyes, the use of well established methods combined with clinical judgement provides for improved consistency in refractive outcomes.

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