Corneal Approaches
By Vikentia J. Katsanevaki, MD, PhD
Cornea-based techniques for refractive surgery have several advantages over lens-based approaches, the first being that they are not intraocular treatments. Second, laser refractive surgery is less expensive than phakic IOL implantation; once a surgeon has made the initial purchase of an excimer laser, the subsequent costs for the practice are minimal compared with the ongoing expense of maintaining an inventory of implantable lenses. The laser is also more widely accepted, as most patients and their families and friends who accompany them to appointments are familiar with lasers. For patients, hearing that a laser will be used to perform their procedure is more comforting than hearing that their surgeon is going to open a hole in their eye and implant a lens.
There are disadvantages to corneal approaches as well. Patients who undergo laser refractive surgery are subject to the sometimes-unpredictable healing response. Regardless of how accurate and optimized a procedure is, surgery still causes trauma to the eye. With phakic IOL implantation, there is no significant healing involved, which is beneficial because this optimizes the patient’s refractive result. A second downside of the corneal approach is that it is subject to anatomic limitations. Not all patients are candidates for laser refractive surgery, because they have either inadequate amounts of corneal tissue for the required ablation or degrees of refractive error outside the laser’s treatment range. Under these circumstances, a lens-based approach is preferred. Additionally, patients who undergo laser refractive surgery are at an increased risk of developing corneal ectasia due to thinning of the residual stromal bed.
For patients who are candidates for either a corneal or lens-based approach, surgeons have varying preferences as to which treatment is best to correct myopia, hyperopia, and astigmatism. This article presents several surgical scenarios in which the excimer laser was successfully used to achieve refractive corrections in patients who also may have benefitted from the use of an intraocular approach.
CASE NO. 1
A 32-year-old woman presented with a stable refraction of -10.50 -1.00 X 70 and pachymetry of 547 μm (Figure 1). Earlier, when we used microkeratomes that cut very thick flaps, this patient could not have been treated with LASIK; however, using sub-Bowman keratomileusis, I was able to make a very thin flip of 79 μm thickness. The assumed correction that the patient needed for plano was a maximum of 146 μm depth, leaving 330 μm of residual stroma, which is well above the 250-μm minimum limit for LASIK. At 9 months postoperative, the patient had a UCVA of 20/20 in the operated eye and was happy with this outcome. Overall, with a limit of about 10.00 D of myopia, patients can be treated with the laser, and if there is enough tissue a good result can be achieved. This patient could also have been treated with a phakic IOL, but I preferred the laser approach.
CASE NO. 2
A 31-year-old man presented with a stable refraction of -6.75 -1.00 X 170 and pachymetry of 513 μm (Figure 2). There was a peculiar bow-tie pattern on his topography as well as some posterior elevation in the posterior surface of the cornea, which makes laser correction a bit tricky. Despite the fact that there was an adequate amount of tissue, one might assume that this patient’s cornea would not be very stable postoperatively, indicating that a phakic IOL should be chosen. However, another option for myopia of up to 6.00 or 7.00 D is PRK, as this procedure does not devote tissue to flap creation or put the stability of the cornea at risk. I performed PRK with mitomycin C (MMC) application, and at 2 years postoperative the patient’s UCVA was 20/10.CASE NO. 3
A 43-year-old man had a stable refraction of +0.50 -2.25 X 176 and pachymetry of 502 μm (Figure 3). The patient had a peculiar topographic pattern and considerable posterior corneal elevation. Again, with high astigmatism, a thin cornea, and posterior elevation, this patient could be at risk if treated with a laser. However, he was 43 years old, which is reassuring because ectactic disorders of the cornea usually occur in a patient’s early 20s and last for about 10 or 15 years. Therefore, because this patient was stable, of appropriate age, and was being treated for only -2.25 D of cylinder, I performed PRK with MMC combined with corneal collagen crosslinking (CXL) with a target of plano. At 18 months postoperative, the patient’s UCVA was 20/10. Again, this was another successful case with the laser in which another surgeon might have preferred a lens-based approach.
CASE NO. 4
A 25-year-old woman presented with a stable refraction of -4.25 -1.00 X 135 and pachymetry of 548 μm (Figure 4). Her topography map showed subclinical keratoconus with an abnormal topographic pattern. This patient could have been an appropriate candidate for phakic IOL implantation. However, I opted to combine PRK with MMC plus CXL to stabilize the cornea. At 4 months postoperative, the patient achieved a UCVA of 20/10.
CASE NO. 5
A 42-year-old man presented with 20/20 BCVA with -3.50 D sphere (Figure 5). He looked like a good candidate for laser correction; however, he had clinically significant keratoconus in the fellow eye. The patient had been treated 6 months earlier in that eye with combined PRK and CXL but had experienced significant healing problems postoperatively. Rather than repeating the same approach in his other eye, with the possibility that his epithelium would not heal properly, I chose to utilize a Visian Implantable Collamer Lens (ICL; STAAR Surgical). At 18 months postoperative, his UCVA was 20/10. Sometimes, patients who initially appear to be candidates for laser correction may, in fact, have a contraindication, making phakic IOL implantation the best treatment option.
CONCLUSION
Both corneal and lens-based approaches to refractive surgery can be used to achieve excellent visual outcomes in well-selected patients. In determining which approach to employ, surgeons should consider the pros and cons of each technique in addition to the patient’s characteristics, daily lifestyle, and predicted results.
Vikentia J. Katsanevaki, MD, PhD, is a refractive surgeon at Orasis Eye Center in Athens, Greece. Dr. Katsanevaki states that she has no financial interest in the products or companies mentioned. She may be reached at e-mail: vikentia_katsanevaki@yahoo.gr.
Intraocular Approaches
By Tobias H. Neuhann, MD
When a patient presents for refractive surgery, there are several factors the surgeon must evaluate before determining which approach—corneal or intraocular—to employ. These include the patient’s type and degree of refractive error, the patient’s age, and the power of accommodation of the lens. Topography should be used to evaluate the regularity of the cornea, as patients with pupils that measure 8 mm or larger often already experience visual disturbances such as halos and glare.
In appropriate candidates, the implantation of a phakic IOL such as the Visian ICL has several advantages over laser refractive surgery for correcting refractive errors. With ICL implantation the cornea and tear film remain untouched, whereas with LASIK the shape and biomechanics of the cornea are modified and the tear film is affected. Visual recovery is fast with both corneal and lens-based approaches; however, the patient’s vision may fluctuate more after LASIK. Laser treatment can also lead to higher-order aberrations, which generally do not occur with phakic IOL implantation. Further, intraocular approaches are more predictable, as there is no regression of effect and no risk of corneal ectasia as with laser approaches. Last, implantation of the Visian ICL does not require postoperative steroid use; we prescribe a topical NSAID postoperatively to control inflammation. Postoperative steroid use in patients treated with laser may induce dry eye or increased IOP.
One potential disadvantage of Visian ICL implantation is the development of cataract if the vaulting of the ICL over the crystalline lens is insufficient. With LASIK, the crystalline lens is untouched, but early cataract development after excimer laser treatment has been reported.
CASE NO. 1
A 21-year-old woman presented with +8.50 D sphere and 20/25 visual acuity. She was intolerant of contact lenses and did not wish to wear glasses. The patient’s topography was normal, pachymetry was 612 μm, anterior chamber depth was 3.0 mm, and no ocular pathology was present (Figure 1). She was implanted with the Visian ICL V3 in both eyes.
At 15 years’ follow-up, the patient’s refraction was +0.75 -0.50 X 125 = 20/25 in the right eye (OD) and +0.25 -0.50 X 171 = 20/25 in the left (OS). She had no ocular pathologies.
Distance between the two lenses with 15 years’ follow-up was small, but a gap was definitely visible, and no sign of anterior subcapsular haze was seen. The patient is now 36 years old and already asking about potential presbyopic treatment.
CASE NO. 2
A 33-year-old woman presented with a refraction of -4.50 -2.25 X 8 = 20/15 OD and -7.25 -2.25 X 2 = 20/15 OS (Figure 2). She was an information technology specialist who drove a lot at night. The patient was contactlens– intolerant and wanted to be spectacle independent. Her mesopic pupil diameter was 7 mm.
The patient was implanted with the Visian Toric ICL (STAAR Surgical), targeting plano in both eyes. Postoperatively, her expectations were fulfilled, and good distance was achieved between the two lenses. Additionally, she experienced a reduction in the incidence of halos and glare following implantation.
CASE NO. 3
A 34-year-old female teacher presented with refraction of -4.5 sphere = 20/25 OD and -4.75 -1.00 X 160 = 20/25 OS (Figure 3). Her profession and daily activities were the reasons she desired refractive surgery. The Belin/ Ambrosio map showed no risk for ectasia (Figure 4), her corneal thickness was 600 µm, and her mesopic pupil measured 6 mm. In this case, LASIK was the treatment of choice. The patient achieved excellent UCVA of 20/15 in both eyes. Nevertheless, she complained of dry eye and unstable vision for more than 3 months. Today, however, the patient says undergoing LASIK was the best decision she ever made.
CASE NO. 4
A 64-year-old woman presented with a refraction of -4.50 -0.50 X 30 = 20/25 OD and -1.75 -0.50 X 177 = 20/25 OS (Figure 5). She was the owner of a high-fashion clothing store, was very active, and had severe dry eye syndrome. Due to her profession and daily activities, she desired refractive surgery, and her expectation was vision better than she experienced with glasses or contact lenses.
Due to the fact that her dry eye symptoms could worsen in the early postoperative phase after corneal refractive surgery, I proposed a clear lens exchange, only in the right eye, to achieve monovision. The result was excellent.
CASE NO. 5
A 25-year-old female soldier presented with -7.75 -1.00 X 0 = 20/15 OD and -8.00 -1.25 X 170 = 20/15 OS refraction. Given her profession, this patient was highly active, and her expectation after surgery was to be able to be in battle without risk. She was implanted with the Visian Toric ICL in each eye (Figure 6), with powers of -10.50 D +1.00 X 85 OD and -9.50 +1.00 X 160 OS. Postoperatively, the patient had a residual -0.50 D of cylinder in the right eye and -2.50 D of cylinder in the left. What went wrong? We determined that a minus sign was forgotten when data were entered into the calculation program.
Fortunately, the intraocular approach is reversible, as implants can be exchanged. Switching a patient’s implant in a case such as this requires no new incisions, no additional cost for the patient, and no real risk (as it is a pure viscosurgery). In addition, it can be performed immediately; you do not have to wait for stabilization as in excimer laser surgery.
CONCLUSION
With the use of lens-based refractive surgery options in appropriate cases, corneal refractive surgery can be kept in its safety zone. There is no regression of effect or induction of dry eye syndrome after refractive lens exchange or implantation of a phakic IOL. Anatomic characteristics, potential side effects, and long-term results are the dominant criteria for decision-making regarding the choice between corneal and lens-based refractive surgery. No technique will solve every refractive problem. Combining both techniques (bioptics) is also a potentially advantageous approach.
Tobias H. Neuhann, MD, is the Medical Director of the AaM Augenklinik am Marienplatz, Munich, Germany. Dr. Neuhann states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +49 89 230 8890; fax +49 89 230 88910; e-mail: sekretariat@a-a-m.de.
