New developments in technologies involving the anterior segment have the potential to change how we practice in the future. Being aware of these new trends will help optometrists remain at the forefront and enable them to provide proper patient education as new techniques are introduced.
The femtosecond laser continues to attract attention. A study of 24 cases (mean age: 34 years) of deep anterior lamellar keratoplasty performed with the femtosecond laser (iDALK) were studied after seven months of average follow up.789/D839 The iDALK procedure was indicated for keratoconus, corneal scars or corneal dystrophies in 82%, 11% and 5% of the patients, respectively.
Preoperative and postoperative distance-corrected visual acuities were 1.57 LogMAR and 0.45 LogMAR, respectively. The average astigmatism decreased from 6.00D initially to 4.80D at the end of the follow-up. When performing iDALK, the surgeon cuts down from the corneal surface to an area of scarred tissue. As shown by the results of this small study, the potential advantage of using the femtosecond laser is that the endothelium and all of the lower levels remain intact. Keeping a patient’s endothelium intact should allow for more structural integrity and hopefully less chance of rejection.
Another study looked at the effects of penetrating keratoplasty (PK) using a femtosecond laser vs. a mechanical trephine in patients with keratoconus.3375/D822 A retrospective comparative surgical case series included 126 keratoconus patients (137 eyes) who had PK. A total of 56 patients (66 eyes) underwent femtosecond-enabled keratoplasty (FLEK). Their visual parameters were compared with those of 60 patients (71 eyes) who had traditional blade trephination penetrating keratoplasty (PKP). The range of follow-up was between three and 12 months. Faster visual recovery and better long-term outcomes were observed in the patients that underwent FLEK.
This study provides great news because the grafts for keratoconus patients are often very large, have significant variability and are associated with slower visual recovery.
The femtosecond laser was also used successfully in a study of an intrastromal procedure that could someday obviate the need for a flap or re-epithelialization in refractive surgery.2543/D1054 The treatment consists of five concentric intrastromal cuts made with the femtosecond laser (Technolas Perfect Vision) without cutting through the epithelium. It replicates a surgical treatment for presbyopia called Intracor.
Using 10 corneas from a human eye bank, researchers made the five concentric intrastromal cuts and then looked at histological sections of each cornea. The aim of this study was to describe the intrastromal incisions’ histology and the ultrastructure on human cornea grafts. The researchers compared their measurements to those referenced by Technolas and found that they were rigorously close.
Another new potential use for femtosecond laser is to correct astigmatism.3380/D827 Researchers evaluated the refractive and keratometric effect of arcuate keratotomy performed on 16 patients using the IntraLase femtosecond laser (Abbott Medical Optics) in patients with high postoperative keratoplasty astigmatism. Arcuate keratotomy performed with the femtosecond laser was found to provide an effective, safe and relatively predictable treatment of high postoperative keratoplasty astigmatism.
In the past, either a toric excimer laser procedure or limbal relaxing incisions with a blade have been needed to surgically correct astigmatism. To be able to accomplish this with a femtosecond laser incision—especially for high levels of postoperative astigmatism—is very promising and needed.
In another study, researchers assessed whether a femtosecond laser could be used to create a corneal pocket safely under a previous LASIK flap as a prelude to implantation of a small aperture corneal inlay for successful treatment of presbyopia in patients with prior LASIK distance vision correction.5767/D1052 Pockets, created in the non-dominant eyes by the femtosecond laser, were 6.5mm wide, opened temporally, and were positioned to leave 250µm of residual posterior stroma. The pocket procedure was performed on seven patients––five male and two female.
The creation of the flaps beneath LASIK flaps showed clear corneas beginning on the first postoperative day. No safety issues were observed clinically and through evaluation with Fourier domain OCT. Such a procedure may allow for the use of a small aperture corneal inlay to treat presbyopia in patients with previous LASIK to improve near uncorrected visual acuity.
In a related study, a corneal inlay called KAMRA (AcuFocus) was placed under LASIK flaps for the correction of presbyopia. The technique showed that both reading ability and reading speed statistically improved two years after implantation.847/D995
A different technology that produces the same benefits was also investigated. ReVision Optics Intracorneal Inlay with LASIK was shown to improve visual acuity at all distances in hyperopic presbyopes.5765/D1050 The inlay led to improved uncorrected visual acuity at near, intermediate and distance for patients undergoing a concurrent LASIK procedure.
Corneal Collagen Crosslinking
Two innovative uses of corneal collagen crosslinking (CXL) were studied. The technique, not yet FDA approved for use in the United Sates, involves the application of riboflavin and ultraviolet light to help correct for ectasia progression in patients who have keratoconus or post-LASIK ectasia. In a prospective, randomized controlled trial, 50 eyes (38 patients) underwent CXL for keratoconus (n=34) or ectasia (n=16).4388
CXL was performed with a UVX system (Peschke Meditrade GmbH) using standard technique. Clinical outcomes—including uncorrected visual acuity, best corrected visual acuity, maximum keratometry, CXL-associated corneal haze and corneal thickness—were assessed and analyzed at intervals up to 24 months. CXL was found to have effectively improved visual acuity and topographic outcomes. It’s a shame that the United States is the only country that doesn’t have access to this technology, which could halt progression of disease in our keratoconus patients.
Additional research suggested that, in the future, we may be able to apply CXL to a transplanted cornea to allow for fixation of the cornea.349/D865 CXL would function as an alternative to sutures, which can irritate the cornea, induce significant astigmatism and lead to infection or rejection.
Some patients have experienced multiple failed corneal transplantations because of graft rejection. The only alternative for them might be the implantation of artificial corneas. One study showed ways to possibly increase the structural integrity of these synthetic corneas.328/D844
The goal of the research was to evaluate the potential of marine sponge-based scaffolds for tissue integration in artificial corneas. The sponge skeleton is a highly porous scaffold with interconnected channels formed by spongin fibers, a type of collagenous material, and calcium carbonate spicules.
The sponge skeleton supported attachment and extensive proliferation of corneal fibroblasts. Increased tear strength of sponge-hydrogel hybrids allowed synthetic corneas to better withstand surgical implantation. The conclusion? Interconnected channels between the sponge skeleton and hydrogel material may further aid in tissue integration and nutrient perfusion.
An artificial cornea can also help after extreme thermal injuries. The Boston Ocular Prosthetic Device was used for exposure keratopathy in 16 eyes of 10 U.S. soldiers injured in Iraq between 2008 and 2010. All of the patients had partial- or full-thickness burns to the face.333/D849 Although the cases involved tragic circumstances, including the death of three of the patients from other injuries, the study showed the capability of this artificial cornea technology to improve ocular surface comfort in some of the most severe corneal injuries.
Meanwhile, a retrospective chart review of Type 1 Boston keratoprosthesis (KPro-1) procedures was performed at a tertiary care eye center between January 2008 and August 2010.348/D864 Outcome measures were based on graft retention, visual acuity and complications. The use of the KPro-1 was found to be a viable alternative for eyes with a poor prognosis with conventional keratoplasty. This research is significant. These patients were previously left blind because standard corneal transplants were no longer an option for them.
Research continues to demonstrate the critical importance of treating dry eye in patients who have had any ocular surgery. In one study, ocular surface disease was the main predictor of failed corneal transplantation.331/D847 This retrospective, non-comparative interventional case series involved eight eyes in seven consecutive patients with ocular-surface disease and limbal stem cell deficiency.
Another study showed the benefits of using anterior segment Visante OCT (Carl Zeiss Meditec) technology to measure and evaluate all structures in the anterior segment, even after a major triple procedure that included PKP, previous anterior chamber intraocular lens (IOL) removal and iris-claw IOL implantation in the anterior chamber.351/D867 Because Visante OCT is a non-contact device, it can easily be used for postoperative assessment of the anterior segment for anatomical changes and complications. It is also very accurate.
Another area of interest is the use of medications after surgery. One study showed that patients on Durezol (difluprednate, Alcon) after ocular surgery had fewer corneal graft failures than those receiving other topical corticosteroids.1978/D959
In another study of 10 patients, difluprednate was found to be effective in the initial postoperative care of PK.365/D881 It was also found to be a viable treatment after other corneal procedures, such as DALK. Special consideration and consistent measurement of IOP in the postoperative period must be taken in the treatment of patients with glaucoma or prior history of a corticosteroid response. Elevation of IOP may occur at one-month follow-up. In our clinic, we use difluprednate on our grafts for the first month and then switch to loteprednol long term. Loteprednol’s potency and safety profile appear to be a very effective for transplant eyes, which require long-term therapy to prevent rejection; this study supports this approach.
Bromfenac (formerly Xibrom and now Bromday, ISTA) is an impressive nonsteroidal anti-inflammatory drug used following cataract surgery procedures. In a study in which the agent was put in a DuraSite vehicle, rabbits were assigned to concentrations of 0.045%, 0.09%, 0.18% or control.476/D1123 All animals were dosed for a period of 14 days and sacrificed on day 15. None of the formulations elicited evidence of ocular irritation or systemic toxicity and no dose-related effects were noted on specific ocular indices.
Surgery of the Future
Trauma that destroys the iris causes severe aesthetic concerns, as well as visual impairment due to photophobia, aberration disorders, glare effects and loss in depth of focus. Up until now, iris reconstruction has been a challenging surgical procedure, requiring large sclera-corneal incisions with poor cosmetic outcome. With a new artificial iris (ArtificialIris, Dr. Schmidt Intraocularlinsen), small self-sealing incisions are possible, enabling fast visual recovery with excellent cosmetic outcomes.449/D1096 The device may be used for complete and partial iris reconstruction.
In another surgical innovation, an injected polymer used after cataract surgery to replace the lens may restore accommodation.852/D1000 The accommodative apparatus of a human eye was mounted in a lens stretcher called the EVAS (developed at the Ophthalmic Biophysics Center, Bascom Palmer Eye Institute), and stretched to a maximum radial displacement of 2.5mm. Quantitative and qualitative differences could be seen in the accommodation response of the natural lens and refilled lens on the EVAS. The natural lens exhibited a viscoelastic type response while the lens refilled with siloxane-based polymer demonstrated a more elastic behavior.
Perhaps someday a lens polymer will be injected into the capsule rather than implanting an intraocular lens.