Dealing with an irregular cornea can be frustrating for both the patient and doctor. Unfortunately, little compares to the frequency of irregular corneas and the associated complaints found in the post-radial keratotomy (RK) patient. The once young, myopic patient is now older—usually hyperopic, presbyopic, with irregular astigmatism and mild to moderate lenticular changes. They often report glare and/or halos, daily fluctuating Rx changes, distorted vision and dry eye. As eye care practitioners, we have all seen these patients in our offices as they seek answers to alleviate their particular visual complaints.
In addition to the usual RK armamentarium of glasses, soft contact lenses and/or RGP lenses, we have gathered a few pharmaceutical pearls to offer some relief for the disheartened RK patient. Keep in mind that studies in this patient population are rare, and there is little printed support for these recommendations. Each patient may report a different success rate. These treatments are considered off-label, but then again, so are many of the indications for which we pharmaceutically treat on a daily basis.
Glare and Halos
Glare and halos are some of the most common complaints from the post-RK patient whose irregular cornea creates a multitude of surgically induced aberrations, including spherical aberrations, coma and trefoil. As you would expect, these complaints are most intense with night driving and other low light activities. Many practitioners use brimonidine off-label for its alpha-agonist effect on the dilator muscle, which keeps the pupil smaller and can decrease the glare and halo in patients with increased aberrations from RK.
One study found the use of brimonidine 0.15% would produce a 1.0mm or more pupillary constriction in a majority of patients under both scotopic and mesopic conditions with less of an effect on photopic pupil size.1
This treatment has also been successful with post-LASIK patients with similar glare complaints and with multifocal patients who complain of halos postoperatively. We recommend Alphagan-P 0.1% (brimonidine tartare ophthalmic solution, Allergan), one drop 30 minutes to one hour before night driving. Literature also suggests the use of brimonidine for night vision complaints.2
Any of the brimonidine products will work, however the 0.1% formulation has the lowest risk of ocular allergy documented at 10%. Alphagan P 0.1% also has the fewest systemic side effects of the product line including somnolence, a concern when recommending its use before driving at night.3 We do not recommend diluting pilocarpine for miosis as the parasympathomimetic side effects such as brow ache and accommodative spasm are not found with an alpha-agonist.
Many RK corneas not only exhibit surgically induced aberrations and irregular astigmatism, but exhibit changes due to the loss of normal corneal nerve architecture.4 Depending on the number of radial incisions the number of transverse incisions, subsequent laser refractive treatments and the age and gender of the patient, dry eye can exacerbate the fluctuating vision and irregular topography characteristic of RK. One study using interferometry demonstrated irregular epithelial and topographical changes post-LASIK and post-RK, which may account for the poor tear stability and increased tear break-up times (TBUT) noted clinically in this patient population.5
The tear film is the most anterior refractive surface of the eye and must be adequate even in normal, non-surgical patients. In RK patients, the tear film proves even more important to avoid exacerbating an already compromised optical system. Don’t forget to treat even mild tear deficiencies in production and/or quality. Restasis (cyclosporine ophthalmic emulsion 0.05%, Allergan), punctual plugs and omega-3 fatty acids are a few examples of treatments that can be paramount in helping your patient’s post-RK quality of vision and ability to comfortably wear contact lenses.
Prescription changes throughout the day are well documented in post-RK patients, and are believed to correlate with normal diurnal changes in IOP.6,7 What is negligible to an intact cornea, however may cause profound changes in Rx for some post-RK patients. This raises the question: If we stabilize or maintain a consistent IOP throughout the day, would the Rx also stabilize? In patients who self report a varying Rx over the course of the day and may present to you two separate morning and afternoon pairs of glasses, consider once-daily latanoprost off-label to stabilize IOP.
We all know prostaglandins have a great pharmacological profile in regards to decreasing mean IOP, as well as variations in IOP throughout a 24-hour period. It is used once-daily with few side effects—now available in generic with little hyperemia compared to its counterparts. Patients with ocular hypertension, suspected glaucoma cases or already diagnosed with glaucoma tend to have the largest IOP fluctuations and may benefit the most from this treatment in more ways than one.
It has been proposed that diurnal variations are worsened by nighttime corneal edema. Although this occurs naturally (to a small amount) in non-surgical corneas, corneal edema may produce a more pronounced effect in an RK patient. The use of an osmotic agent such as Muro-128 5% (sodium chloride hypertonicity ophthalmic ointment 5%, Bausch + Lomb) at bedtime may also help to stabilize the hyperopic to myopic diurnal prescription shift that is typical post-RK.
Although RK patients can be challenging, we hope these pharmaceutical pearls might make dealing with their complaints less frustrating.
1. Thordsen JE, Bower KS, Warren BB, Stutzman R. Miotic effect of brimonidine 0.15% ophthalmic solution in normal eyes. J Cataract Refract Surg. 2004 Aug;30(8):1702-6.
2. Edwards JD, Burka JM, Bower KS, et al. Effect of brimonidine tartrate 0.15% on night-vision difficulty and contrast testing after refractive surgery. J Cataract Refract Surg. 2008 Sept;34(9):1538-41.
3. Allergan. Alphagan P 0.1%. Available at: www.alphaganp.com (accessed March 2012).
4. Namavari A, Chaudhary S, Sarkar J, et al. In vivo serial imaging of regenerating corneal nerves after surgical transection in transgenic Thy1-YFP mice. Invest Ophthalmol Vis Sci. 2011 Oct 11;52(11):8025-32.
5. Szczesna DH, Kulas Z, Kasprzak HT, Stenevi U. Examination of tear film smoothness on corneae after refractive surgeries using a noninvasive interferometric method. J Biomed Opt. 2009 Nov-Dec;14(6):064029.
6. Schanzlin DJ, Santos VR, Waring GO, et al. Diurnal change in refraction, corneal curvature, visual acuity and intraocular pressure after radial keratotomy in the PERK study. Ophthalmology. 1986 Feb;93(2):167-75.
7. Kemp JR, Martinez CE, Klyce SD, et al. Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the prospective evaluation of radial keratotomy study. J Cataract Refract Surg. 1999 July;25(7):904-5.