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Fully explore possible etiologies of postop refractive surgery symptoms
First confirm cause of symptoms
Joseph Stamm, OD, FAAO: When presented with subjective symptoms of glare, starbursts and halos, the triad of night vision complaints most often associated with refractive surgery, it is vital to assess their true etiology.
Assessing scotopic pupil size is an essential first step. If the patient’s treatment records are available, comparing ablation zone and pupil size may indicate whether symptoms are related to pupil size. Knowing which laser was used for the treatment is important. The wide transition zones of a flying spot laser such as the Bausch & Lomb Technolas 217 create an effectively larger ablation zone than the same diameter ablation using a scanning slit laser. Corneal topography can often identify harsh transition zones with a diagnostic mid-peripheral “red ring.” Topography is also useful in determining whether the ablation is centered or if the patient has a central island.
An accurate refraction is critical. Subtle undercorrections in myopes can dramatically decrease the quality of night vision. Residual astigmatism, especially oblique, can be contributory. When assessing presbyopes who have undergone monovision procedures, look at the anisometropia as a potential cause for symptoms. Having the patient wear a soft contact lens to “undo” his or her monovision may identify the cause of the symptoms.
Wavefront sensing is the ultimate tool for determining the cause of a patient’s symptoms. Halos tend to be caused by spherical aberration. Coma and secondary astigmatism also degrade an image. Elevated levels of higher-order aberrations decrease visual quality, and that is magnified by pupillary dilation.
In the first year postop, it is also important to assess pre-ocular tear film stability. A poor tear film, with or without epithelial disruption, can result in a decrease in optical quality at night.
Treatment for night vision symptoms can be as simple as a pair of glasses to wear as needed, use of a viscous artificial tear and punctal occlusion or re-treatment. Until wavefront-driven customized ablation is approved by the Food and Drug Administration for re-treatments of higher-order aberrations, we may be limited to palliative care, such as using Alphagan (brimonidine tartrate ophthalmic solution 0.20%, Allergan) 30 minutes before dusk to limit pupil dilation or increasing the illumination of the car’s dashboard instruments to induce slight pupillary constriction.
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Elucidate exact nature of symptoms
Marc R. Bloomenstein, OD, FAAO: The existence of pupil-related symptoms following LASIK is a very controversial issue. Research has not proven that a narrow treatment diameter is correlated with postoperative symptoms. This is further evidenced by the tens of thousands of asymptomatic patients who had LASIK performed when pupil size was not pertinent. However, when a symptomatic post-LASIK patient presents with large pupils, my first instinct is to prove that the pupils are not related to the problem. In my experience, patients who demonstrate a normally enlarged treatment diameter may still present with symptoms.
The normal battery of tests should be performed, including a postoperative topography, and a thorough cycloplegic refraction is paramount to elucidate the exact nature of the symptoms. Most postoperative glare and halos are a result of under- or overcorrection and are not induced by large apertures. In fact, patients with residual refraction will have reduced contrast sensitivity and scotopic symptoms that resemble large pupil complaints. I will actually put the refraction in the phoropter, dim the lights and assess the quality of the vision (or prescribe contacts for night driving) to rule out even the smallest amount of refractive error.
When the refraction is discounted as the culprit, I will turn to the pupil. The use of one drop of brimonidine 0.20% at dusk will stabilize the pupil for the vast majority of patients and will give an artificially enlarged treatment zone. Should the drops prove to help the symptoms, then I recommend surgical enlargement of the treatment diameter. This treatment may induce hyperopia, and, therefore, the risk-benefit ratio must be evaluated prior to any re-treatment, regardless of the causes.
When all treatment regimens are exhausted and the symptoms are still present, I then look to a higher order. Yet, without the use of a wavefront analyzer, I am only surmising this diagnosis.
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A variety of etiologies are possible
Jeffrey M. Augustine, OD: Visual disturbances after LASIK are due to a variety of etiologies. Continued overemphasis of pupil size as the primary factor for these visual disturbances is incorrect. According to Steven E. Wilson, MD, professor and chairman at the University of Washington in Seattle, there is no direct correlation or relationship between pupil size and quality of vision following LASIK. However, the higher the attempted laser correction (myopic, hyperopic or astigmatism), the higher the likelihood that the patient will have visual aberrations postop. In addition to refractive error issues, several other risk factors may exist for postop LASIK optical aberrations. Other causal factors for optical aberrations are corneal curvature changes, small flap diameter, size of ablation zones, postoperative residual refractive error, strabismus and dry eye syndrome.
Preoperative counseling can help you avoid postoperative disappointments. For example, a 7-D myope, with preop average K values of 40.50 is at greater risk of visual disturbances postop than the same 7-D myope with an average K value of 45.00 preop. The greater the attempted corneal curvature flattening or steepening, the greater the risk for visual aberrations.
Prevention is the best way to avoid postoperative LASIK aberrations. A critical preop evaluation should point out risk factors, such as high refractive errors, myopia greater than 6 D, hyperopia greater than 4 D and astigmatism greater than 3 D. Also, corneal K values that would surgically result in flattening the cornea below 35.00 or steeping the cornea above 50.00 are a risk factor for aberrations.
Most surgeons will adapt the laser surgery to better accommodate patients with larger pupils. With current excimer laser technology, it is now possible to expand ablation optical and blend zones to help aid in the prevention of visual aberrations. Laser manufacturers will continue to develop software changes to further expand these zones.
There are three ways to treat postoperative LASIK aberrations: optically, pharmaceutically and surgically.
Optically, look for and treat residual refractive errors. Look especially hard for small residual uncorrected astigmatic errors. Even small refractive errors can produce significant visual symptoms.
Try fitting patients with –0.50 D overcorrected prescription — “night vision glasses” with antireflective coating and a 15% yellow tint.
Perhaps the most common cause of “glare” symptoms can be attributable to dry eye etiology. Be very aggressive in dry eye management, including early consideration of the use of punctal plugs. Inferior corneal dryness is a common cause for oblique astigmatism and will be picked up through K reading examination as oblique astigmatism and blurred mires.
Try one drop of Alphagan P (brimonidine tartrate ophthalmic solution, 0.15%, Allergan) 1 hour before dark.
Another way to decrease the full dilation of the pupil is to use one drop of 1/8% pilocarpine 1 hour before dark.
Corneal thickness and residual refractive error permitting, ablation optical/blend zones can be expanded. For example, a patient who I recently managed had myopic LASIK performed several years ago, had been treated with a 5-mm optical zone and complained of difficulty with glare, blur and halos. The patient’s residual refractive error was –75 –0.50 × 180. The patient was 20/20, and corneal thickness was 493 µm. During the enhancement procedure, the surgeon expanded the optical zone to 6.5 mm and the blend zone to 7.5 mm. Postoperatively, the patient complains of no aberrations and sees 20/20 without correction.
Without enough corneal thickness, LASIK enhancement techniques may not be able to be performed safely. It is always important to maintain the 250-µm bed thickness.
Other ablative techniques that can be used to decrease the risk of aberrations are to combine a hyperopic ablation pattern with a myopic ablation pattern. With this technique, the blend zones may be extended out to 10 mm, dramatically reducing the chances of visual aberrations.
As a clinician, don’t get pigeonholed into thinking that the pupil size is the only etiology for postoperative LASIK visual aberration. The etiology is multifactorial.
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First try an RGP lens
Loretta B. Szczotka, OD, MS, FAAO: A somewhat simplistic approach I always use is to simply apply a rigid gas-permeable (RGP) for a contact lens over-refraction. A rigid lens will correct residual refractive error and any corneal irregularity and, therefore, some of the higher-order aberrations. If the glare that patients notice after refractive surgery is immediately resolved with the application of an RGP in dim and normal room illumination, then your problem is solved. But it is not always that easy. Usually, the patients who respond so positively with an RGP have obvious corneal irregularity such as a central island. If the glare, arcs, starbursts and halos remain after applying an RGP in various illuminations, unfortunately, the problem may be due to large pupils and other treatment options (such as Alphagan) should be considered.
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