3046: diurnal visual fluctuations in RK eyes
Addressing the diurnal refractive shift in radial keratotomy eyes
Radial keratotomy was a popular refractive procedure in the late twentieth century, offering millions of patients a large degree of spectacle freedom. Decades later, these patients develop cataracts and progressive hyperopia as the cornea continues to flatten. In addition, these deep corneal stromal incisions can cause diurnal fluctuations as the corneal architecture and power can waver daily. When these patients present to our clinic for cataract surgery, we can address the lens opacity, the refractive error, and the diurnal fluctuations at the same time.
Patients report a predictable corneal flattening and steepening throughout the day that leaves patients struggling with unreliable, shifting sight. In some patients this means better vision in the day, whereas others note the optimal time is evening. When these post-RK patients eventually develop cataracts, choosing the most suitable intraocular lens and refractive target becomes an important decision.
Monofocal lenses offer little forgiveness for shifting refractive error because they have a narrow depth of focus. Traditional diffractive multifocal IOLs can severely compromise contrast sensitivity when paired with the pre-existing higher-order corneal aberrations due to the prior radial keratotomy. The optimal surgical solution is often to utilize non-diffractive extended depth of focus (EDOF) IOLs.
By providing a continuous, wider range of focus, an EDOF lens acts as an optical buffer against the diurnal corneal fluctuations inherent to post-RK eyes. To understand why this method is effective, we must look at the biomechanics of the post-RK cornea. RK incisions frequently extend to 90 percent of the corneal depth or more, permanently weakening the structural integrity of the stroma. Overnight, while the patient is supine with eyelids closed, mild corneal swelling combined with intraocular pressure dynamics causes the central cornea to flatten. This structural shift induces a hyperopic shift in the morning.
As the day progresses, atmospheric exposure and normal tear film evaporation cause the central cornea to gradually steepen, shifting the eye back toward myopia by evening. This continuous daily cycle can result in a refractive variation ranging from 0.50 D to well over 1.50 D within a twelve-hour window. A patient implanted with a standard monofocal lens targeted for distance will experience significant visual compromise in the morning during a hyperopic shift, and will lose intermediate clarity by evening as the cornea steepens. An extended depth of focus lens changes this outcome by altering the total optical depth of field instead of splitting light into discrete focal points.
Modern non-diffractive EDOF designs deliver roughly 1.75 diopters of continuous visual range. When an RK cornea fluctuates by 1.00 D or 1.25 D throughout the day, that entire refractive movement takes place safely inside the landing zone provided by the EDOF IOL. Rather than experiencing sharp drops in visual acuity as corneal power shifts, the patient maintains a stable baseline of functional vision. Non-diffractive wavefront-shaping EDOF IOLs are particularly advantageous because they preserve a good degree of contrast sensitivity and tend not to produce central halo rings that could compound the irregular astigmatism already present in post-RK eyes. Achieving predictable outcomes in these eyes requires meticulous pre-operative planning and strategic biometry targets.
Surgeons should rely on dedicated post-refractive formulas such as the Barrett True-K or online post-refractive calculators. Because post-RK biometry calculations historically tend to err toward unwanted hyperopia, aiming for a slight myopic target of -0.25 D to -0.50 D provides a critical safety buffer. This slight myopic bias ensures that even when morning flattening occurs, the overall refraction remains within the functional range of the EDOF optic rather than drifting into hyperopia.
During surgery, creating a well-centered, 360-degree capsulorhexis is vital to guarantee lens stability and prevent optic tilt, which could otherwise worsen corneal aberrations. Depending on the number and spacing of the radial keratotomy cuts, surgeons may be required to make a scleral incision to avoid intersecting these old incisions (figure 1). If intersected with a new incision, these older radial keratotomy cuts may open and cause leakage thereby requiring suturing.
The EDOF IOL optic should be carefully centered in the visual axis and if there is also a toric correction on the optic, it should be rotated to align the steep axis of corneal astigmatism (figure 2). At the end of the procedure, the main incision can be sutured to ensure stability and then the entire cornea can be checked with a fluorescein dye leakage test (figure 3). The standard infusion pressure used during cataract surgery can sometimes lead to microscopic leakage from these old radial keratotomy incisions. The dye test ensures that the eye is completely watertight.
Proper patient counseling is essential because while we can do cataract surgery to improve clarity, treat the refractive error, and even buffer the diurnal fluctuations, it is not possible to deliver perfect vision due to the limitations of the RK. These patients often have high expectations, having previously enjoyed spectacle independence after their initial refractive procedures. It is crucial to explain that the EDOF lens functions like a shock absorber for their sight rather than a complete cure for corneal instability. Patients should understand that while their daily visual fluctuations will be heavily dampened, they may still require mild reading glasses for small print or reading text in low light. By leveraging EDOF technology to buffer these refractive shifts, surgeons can turn a frustratingly unpredictable clinical dilemma into a reliable and rewarding result for post-RK patients.
