All surgeons will have a refractive surprise at some point in their careers. What differentiates a refractive-minded cataract surgeon from the rest is the willingness to invest in accurate diagnostics and address the postoperative miss.
The goal of a refractive cataract surgeon is to achieve a patient’s desired postoperative refraction, often emmetropia, with or without presbyopia correction after cataract surgery. The hurdles to accomplish this vary, including skills training, access to diagnostics and excimer lasers and, most of all, the anxiety of having to deliver on the promises made with out-of-pocket costs. Similarly, IOL technology is everchanging and it can be difficult to keep up with the caveats of each technology.
Here, I explain how refractive cataract surgeons can optimize their patients’ postoperative outcomes.
PREOP STRATEGIES
Communication
The first step is to talk to your patients. This involves understanding how they use their eyes, including occupation and hobbies, and their current eyeglass prescription. This critical information will ideally help guide the IOL selection and level of astigmatic correction prior to cataract progression.
The patient needs to understand that there is nothing better than what “mother nature” gave us in terms of vision quality. Current IOL technology
will only attempt to meet the needs of our patients. Fortunately, current IOL formulae allow us to achieve our refractive target 85-90% of the time depending on the underlying anatomy and technology chosen. However, the true test of the refractive surgeon is the ability and willingness to make it right and correct the residual refractive error.
Diagnostics
Measure twice and cut once. Must-have diagnostics for a refractive-minded cataract surgeon include a biometer, topographer with Placido imaging, an autorefractor and spectral domain macular OCT. Tomography is helpful but not absolutely necessary unless laser refractive surgery will be used as a postoperative tool for enhancement.
All technology is only as good as its accuracy and reliability. It is imperative that technicians and surgeons understand when diagnostic readings are unreliable and have a low threshold to repeat testing. It’s helpful to obtain two readings from different biometers on the same day or have the patient return on a different day to check for consistency and accuracy.
Inevitably, some days we are less observant than others due to volume of patients and clinic flow. However, having a checklist in your preoperative assessment to avoid missing the following diagnoses will save postoperative angst: ocular surface disease, prior contact lens use (soft or rigid), prior laser vision correction (LVC), corneal scarring/ectasia or irregularity such as Salzmann’s degeneration or epithelial basement membrane dystrophy, Fuchs dystrophy, epiretinal membrane or AMD. Understanding these common pitfalls in examination will save the surgeon from an avoidable postoperative refractive surprise.
POSTOPERATIVE STRATEGIES
Help is available
In the event of a postoperative refractive surprise despite perfect preoperative preparation and ocular surface optimization, some simple techniques are available to help achieve excellent results. This knowledge should give the cataract surgeon confidence to move into becoming refractively minded and decrease performance anxiety.
Ocular surface analysis
Postoperative topical medications often have preservatives that can challenge the ocular surface and cause punctate epithelial keratopathy. The surgeon should resist the urge to consider refractive enhancement with peripheral corneal relaxing incisions (PCRIs), LVC or IOL exchange until the Placido imaging on topography normalizes and the patient is off all postoperative drops.
Additionally, an exposure pattern of corneal staining should be identified as many of our patients have had cosmetic procedures that cause lagophthalmos or they are on CPAP machines that cause air flow exposure. Consider a thicker artificial tear at bedtime if this pattern is identified postoperatively.
In the event that the ocular surface is normalized but a refractive error remains, the surgeon should act.
Contact lens overrefraction
A contact lens overrefraction is critical to evaluate if the correction will achieve adequate visual quality. In the case of diffractive dysphotopsia, it will also help determine if the visual discomfort is coming from the lens or refractive error. The most common scenario where this is helpful is a low myopic residual error that is correctable with a soft contact lens overrefraction. LVC in the form of LASIK or PRK is advisable.
Wavefront analysis
It is often helpful to use wavefront analysis (Scheimpflug, ray tracing, dynamic skiascopy) in patients who are post-corneal refractive surgery, have ectatic disease such as keratoconus or have corneal scarring. These patients commonly evade accuracy in IOL calculations and measurements. Wavefront analysis measures higher order aberrations, pupillometry, chord mu/angle kappa/angle alpha and point spread functions. In conjunction with a hard scleral contact lens diagnostic trial, these technologies will help determine if the refractive miss is best treated by eyeglasses, scleral lens, IOL exchange or piggyback secondary IOL.
Posterior capsule examination
If a patient was happy 1-2 months after surgery but reports hazy vision subsequently, the surgeon should feel comfortable performing a Nd:YAG capsulotomy and then reassessing the refractive error. If the posterior capsule is clean and there is a residual refractive error, the surgeon can feel comfortable proceeding with some type of enhancement in the form of PCRI or LVC. However, surgeons often wait 6-8 weeks. In the event that the posterior capsule is fibrotic, and there is no evidence of debilitating dysphotopsia, many will open the posterior capsule prior to a refractive enhancement.
Peripheral corneal relaxing incision
A common refractive outcome is the under correction of against the rule astigmatism such as +0.50 -0.75 x 95 (-0.25 +0.75 x 005 in plus cylinder). In this scenario, if the spherical equivalent is close to plano, a quick in-office PCRI can solve the problem. Adjustable diamond knives designed for slit lamp use (Mastel) or more affordable MST/Epsilon diamond knives set at 550 microns and markers can turn an unhappy patient into a happy patient. Remember, we treat on the refraction and not the topography. Popular nomograms include the Donnenfeld, Nichamin and Wörtz-Gupta.
A quick reference: 1mm=10 degrees and paired 30 degree PCRIs treat 1D of cylinder. Mark the 90- and 180-degree axis at the slit lamp for reference. Use a marker to indicate the intended axis for PCRI treatment, measure the pachymetry in that area and set the diamond blade at 80% of the pachymetry to avoid perforation (Figure 1).
Laser vision correction
LVC is best used when there is a refractive miss >-0.75 sphere with or without astigmatism or a small hyperopic outcome <SE 1.5D and the spherical equivalent will not be plano with an in-office PCRI. This scenario is best treated with LASIK or PRK 6-8 weeks postoperatively. As mentioned, fibrosis of the capsule or posterior capsule opacification should ideally be addressed prior to LVC enhancement.
Toric IOL rotation
The most common reasons for residual astigmatism postoperatively include inaccurate measurements, inaccurate placement on axis due to marking errors/cyclorotation, postoperative toric rotation or IOL tilt. Remember to dilate and check the IOL orientation prior to any intervention.
In the event there is residual astigmatism due to a rotation of a toric IOL, the surgeon should reference Berdahl & Hardten Toric IOL Calculator (www.astigmatismfix.com). This will require a repeat postoperative biometry and an accurate postoperative refraction. The software will help determine if the IOL should be exchanged for a different power or rotation alone is recommended. Toric IOL rotation does not correct spherical equivalent refractive errors.
When rotating a toric IOL, it is recommended to wait at least 1 week to get accurate measurements, use a cohesive ophthalmic viscosurgical device (OVD) or irrigation alone when possible to free up the IOL. Some haptics will fibrose at the terminal bulb, which must be freed up or the IOL will rotate back to the undesired location.
IOL exchange or piggyback IOL
IOL exchange should be considered with a hyperopic surprise or extreme refractive miss. The Barrett Rx IOL exchange formula (https://calc.apacrs.org/barrett_rx105/) or a shortcut 1.2 x SE for a myopic outcome and 1.5 x SE should be considered for a hyperopic outcome (Gills/Hoffer). Understanding the unique characteristic of haptic design can help the surgeon understand the necessary maneuvers that will result in a positive experience (Figure 2).
Some surgeons may advocate placing a piggyback IOL in the case of a hyperopic outcome. Piggyback IOLs can be considered depending on surgeon expertise, adequate endothelial cell density >1200 cells/mm2 and ACD >3.5-4 mm. There is a limited IOL selection available in the correct powers for piggyback placement. In my experience, the silicone L161AO (Bausch + Lomb) is most friendly in the sulcus, although it is a fully square edge IOL. The recommended acrylic IOLs for off-label piggyback placement include Sensar (J&J Vision) AR40M and AR40E as its edge design is rounded anteriorly but square posteriorly.
Unfortunately, acrylic fully square edge IOLs in the sulcus can be associated with significant iris chafing (Figure 3).
Light Adjustable Lens
If a patient is implanted with an RxSight Light Adjustable Lens, a small postoperative refractive error is usually planned, often in the hyperopic direction. This error can be treated once refractive stability has been achieved using a Light Delivery Device to deliver ultraviolet (UV) light to the lens for the purpose of moving silicone macromers around inside the optic to achieve a change in lens shape. Spherical and cylinder corrections of ± 2.0 D can be achieved using this technology. Once the desired refraction is obtained, further spontaneous changes in power due to accidental environmental UV exposure are prevented by lock-in treatments.
With these tools we can all be refractively-minded surgeons and give the best outcomes to our patients. OM
