What is Refractive Surprise?

What is refractive surprise?

Introduction

LASIK corrective vision surgery has been a fantastic advancement that has freed many people of their glasses and contact lenses. Currently, there is no correlated instance of cataracts related to LASIK surgery. As the recipients of LASIK age however, several will develop age-related or condition-related cataracts that will have to be addressed. Cataract surgery is still successful in LASIK patients, but there can errors when determining the strength of the Intra-Ocular Lens (IOL) using conventional methods when the patient has had previous LASIK surgery. Difficulties arise when trying to measure the curvature of the cornea, and as a result, the optical strength of the IOL gets underestimated, leaving the patient with clear but inaccurate vision. It should be noted that such IOL implantation errors usually result in a 'refractive surprise' wherein an unexpected/unintended post-operative refractive outcome occurs.

Definition of refractive surprise

Technically, the term “refractive surprise” can be defined as the significant differences between the post-operative refraction and the pre-operatively planned result. Like the general population, some of LASIK patients can eventually develop cataracts. In such patients, the altered corneal surface following LASIK prevents accurate measurement of intraocular lens power for cataract surgery. This may result in a “refractive surprise” following cataract surgery and exposes such LASIK patients to increased risk of repeat surgeries.

Refractive surprises after lens surgery are quite frequent, with 100% prevalence if the adequate corrections are not made. There are two reasons for this: a faulty calculation of the corneal power and an inadequate estimation of the effective lens position (ELP).

Why would LASIK impact my cataract surgery success?

It must be noted that cataract surgery is still successful in LASIK patients, but there can errors when determining the strength of the Intra-Ocular Lens (IOL) using conventional methods when the patient has had previous LASIK surgery. Difficulties arise when trying to measure the curvature of the cornea, and as a result, the optical strength of the IOL gets underestimated, leaving the patient with clear but inaccurate vision. To explain this, it has been suggested that after corneal refractive surgery such as LASIK, the utilization of the measured keratometric value without any correction can produce a faulty calculation of the intra-ocular lens power. Thus, such a patient treated for myopia who undergoes cataract surgery will come out hypermetrope and on the contrary, if the patient was previously treated for hypermetropia after cataract surgery will exhibit myopia. Therefore, it is widely believed that the success of cataract treatment after LASIK depends heavily upon accurate calculations of pre-LASIK and present corneal measurements. Therefore, patients needing cataract treatment after a prior LASIK treatment would be best treated by a skilled ophthalmologist who is well-versed in performing both procedures.

Why haven’t existing methods worked well?

It shall be noted that many errors in IOL implantation reported are not complex technological issues, but occur because of misfiling or misreading of biometry printouts, transcription mix-ups, and communication breakdowns between the operating surgeon and nursing staff. It is true that one of the major causes of incorrect IOL implantation and, hence, the resulting refractive error is attributed to a number of existing methods such as problems obtaining accurate biometry; problems matching biometry to patients; problems matching correct IOL implant to correct patient and to laterality. Each of these is a microcosm of the challenges of surgical care such as correctly capturing and then matching correct data to correct patients. On the basis of these themes, certain potential safety improvement advice can be advocated to seek to reduce wrong IOL implantation.

Are new measurement techniques required for every type of cataract surgery?

While newer advancement in surgical techniques, IOL power calculation and IOL models have reduced the incidence of refractive surprises associated with cataract surgery, the post op refractive surprises do occur. For the same reason, surgeons are replacing IOLs for a number of reasons, which fall into several broad categories namely post cataract surgery high refractive surprises due to incorrect IOL power calculation, dislocation and decentration, optical aberrations and wrong IOL insertion. In post cataract surgery refractive surprises cases extraocular aids (contact lens, glasses), an IOL exchange, LASIK, Piggyback IOL implantation may be the options to deliver satisfaction and good vision to the patient.

What options do surgeons have if they discover the wrong IOL has been implanted?

Post-operative “surprises” do occur from time to time either as a result of faulty biometry, insertion of the wrong IOL power or faulty IOL labelling by the manufacturer. The problem is how to deal with these. Most patients will be satisfied with a spectacle correction. Surgical alternatives are IOL exchange, which can be technically difficult if the IOL is fibrosed into the bag, in addition to the risk of damaging the capsular bag or cornea (as well as the risks involved in any intraocular operation). Another possibility is the insertion of an appropriately low powered IOL as a “piggy back” procedure into the ciliary sulcus, leaving the original IOL in the capsular bag; a variation of this theme would be to insert a toric IOL to correct both spherical power and astigmatism. At present, these are only available as a plate optic lens, which requires “in the bag” insertion. The final possibility would be excimer laser refractive surgery.

What are some of the new devices and methodologies for accurately measuring lens strength?

To avoid the incorrect IOL implantation, scanning and keratometry are critical in lens calculations. Any previous refractive surgery (such as LASIK) must be considered. Biometry calculations should be performed on both eyes simultaneously and repeated if an asymmetric or unexpected result is obtained. First, on a technology level, ocular biometry should be carried out with the most up to date, accurate biometric equipment and by appropriately trained staff. Advanced technology biometric instruments with improved signal to noise ratio incorporating anterior chamber depth measurements including third- and fourth-generation biometric formulae are available and should be used.

Have you experienced refractive surprise? We'd love to hear your story in the comments section.

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Comments

Refractive surprise sounds scary. Why are they so frequent. Getting cataracts does not sound like fun. How can you avoid this with lasik surgery?