Ophthalmology practices now have many advanced technology options to help their patients achieve the best post-operative refractive outcomes following cataract surgery. Many of the pre-operative tests to assist with IOL selection are essential for all patients, while some are supplementary tools that a surgeon may choose to incorporate.
Here are the pre-op tests and tools that aid in a successful IOL selection.
Refraction and visual acuity
Success begins in the examination room at the patient’s initial consultation with the surgeon. The key elements are an accurate pre-op work up, which includes obtaining an accurate refraction and best corrected visual acuity (BCVA) and recording lensometry readings if the patient presents with glasses. If the patient’s pre-op BCVA is 20/40 or worse, a pinhole should be used to determine visual potential. Some practices may utilize a potential acuity meter to determine the patient’s visual potential following cataract surgery.
The pre-op refraction and acuity are critical to track outcomes and for IOL optimization of the surgeon’s A-constants after obtaining a stable post-op refraction and BCVA. Without tracking outcomes, you won’t know where you are and what changes you need to make to get where you want to be.
Patient history and preferences
A pre-op lifestyle questionnaire completed by the patient is typically utilized to determine the impact cataract symptoms have on activities of daily living and to determine the patient’s post-op vision preferences and desires for spectacle independence. An active patient who drives, is employed, or has hobbies that require distance vision will have very different needs than a patient who is less active and spends their day reading. Visual preferences will determine the post-op refractive goal of an IOL power for best distance acuity vs. near vision or monofocal goal.
Carefully review the patient’s ocular and medical history along with chief complaint. For example, is the patient most bothered by night driving difficulties and impacted by glare, halos, or starbursts around lights at night? In this case, obtain glare testing and record the acuity to demonstrate that the patient may experience sensitivity and vision loss secondary to glare situations. Many visual acuity systems have glare testing built in, or you can utilize a brightness acuity meter.
OSD and corneal evaluations
During the pre-op examination, the surgeon assesses the patient’s cornea for ocular surface disease that would impact corneal measurements. Many physicians recommend treating the ocular surface disease first, then having the patient return for a second corneal examination to repeat the corneal measurements, which are critical to the IOL power calculation.
Corneal curvature measurements include keratometry, topography and tomography. Errors in keratometry are one of the greatest attributors to IOL power miscalculation.
K values are quickly and accurately obtained using optical biometers. The evolution of optical biometers has been one of the best technology innovations for improved patient outcomes. Examples of optical biometry units include IOLMaster (Zeiss), Lenstar (Haag-Streit), and Pentacam AXL (Oculus), which are one-click, non-contact methods that improve accuracy, patient comfort, and chair time. K values should be obtained on each patient multiple times with several devices — biometer, topographer and tomographer. Obtaining consistent and reproduceable measurements ensures the best outcomes.
Manual keratometry should not always be considered obsolete. It may be useful to verify differences in other K values obtained, so keep staff trained on how to obtain a manual keratometry reading.
What is the difference between topography and tomography? Topography maps the curvature of the surface of the cornea, while tomography looks at the entire cornea — anterior and posterior surfaces. Obtaining consistent measurements to determine the amount of astigmatism and the axis measurement is essential for the surgeon to determine if patient would benefit from a toric IOL.
During the pre-op examination, the surgeon also evaluates the patient’s retina to look for any pathology that would impact post-op results. Many surgeons commonly perform OCTs to identify fundus pathology, such as an epiretinal membrane, that could result in an unhappy patient who anticipated a better visual outcome.
Surgeons may need to be perform B-scans when they cannot visualize the retina due to dense cataracts. B-scans can determine presence of a retinal detachment that could impact the decision of whether to proceed with planned cataract surgery.
Aberrometry is another tool utilized in many practices. It is used to determine the amount of spherical aberration a patient may have, which guides the decision on which IOL type to implant.
For example, aberrometry can assess the quality of patient’s vision and any high or low order aberrations.
Axial length measurements
Axial length measurements are most commonly performed with an optical biometer, with ultrasound A-scans performed in the circumstances when the biometer cannot provide reproduceable readings. Though optical biometers are considered by some as “point-and-shoot” technology, it is important the technician performing this test is trained to recognize errors and inconsistencies and to repeat the measurement or obtain an ultrasound A-scan. I am an advocate of having the practice’s best, highly trained technicians perform measurements essential for an accurate IOL calculation.
Strong communication between the surgeon and the technician is very important so that the technician can alert the surgeon to any difficulties or inconsistencies that he/she may have experienced during the testing process. Communicating post-op surprises is important so that each case with a post-op refractive error can be reviewed, the reason for error can be determined, and the error corrected in the future. If post-op target is missed by .50 D, that review should occur — do all of these readings we have taken align with patient history and examination?
With the pre-op testing and examination complete, it is time to review the IOL calculations. Remember: no single formula fits all eyes.
Use multiple newer generation formulas for all patients. There is no need to give special consideration to post-refractive surgery eyes, long eyes, and short eyes, because newer generation formulas take these outliers into account. Outdated formulas cannot be used on these patients, because these were developed for average length eyes.
Newer optical biometry devices typically have in their systems newer formulas, which make calculations easy to run and avoid human error when manual entry is performed. These formulas include Barrett Universal 11, Hill-RBF, Ladas Super and Holladay II, Olsen, and Haigis.
Remember quality, consistency, reproducibility of measurements, education, and communication between surgeon and technician afford you happy patient results, which is the ultimate goal with any cataract surgery. OP