Benefits of topography-guided treatments for irregular corneas
Special to Ophthalmology Times®
Topography-guided treatment for irregular corneas can improve patients’ best-corrected visual acuity (BCVA). Easy to plan and perform, the technique is supported by software to do the calculations.
Irregular corneas can be caused by several factors, including scarring following contact lens infections, keratoconus, and ectasia.
Patients with irregular corneas can be candidates for customized approaches such as topography-guided treatments rather than standard procedures.
Many surgeons are unwilling to treat irregular corneas with transepithelial photorefractive keratometry (PRK) because they are unsure of the outcomes.
They would rather prescribe contact lenses or perform traditional phototherapeutic keratectomy (PTK) because these are easier options in patients who have membrane dystrophies.
However, these methods are not suitable for treating an irregular cornea because it is not clear whether the irregular astigmatism will worsen.
One option is to combine conventional refractive surgery with topography-guided surgery so that even a small variation in the corneal surface can be identified for correction.
This option provides a great opportunity for treatments in patients who have visual complaints caused by corneal irregularities.
Topography-guided treatment allows restoration of the cornea and softens the irregularity of the cornea and produces good refractive results.
When evaluating patients for epithelial irregularity and irregular corneas that are suitable for PTK or a single-step transepithelial PRK, I take the traditional measurements that are common in every patient: refraction; BCVA; slit-lamp examination; fundus examination; intraocular pressure (IOP) measurements; anterior segment optical coherence tomography (OCT) to identify the depth of the corneal opacity (Figure 1); and OCT to assess the macular, retinal nerve fiber layer and ganglion cells.
I integrate topographic images and data from 2 anterior topographic screening tools (Atlas 9000, Carl Zeiss Meditec and Pentacam, Oculus).
I integrate the topographies obtained with the Atlas 9000 into a planning station (CRS Master, Carl Zeiss Meditec; Figure 2) and use the Pentacam to analyze the evolution of the corneal shape, specifically changes in total corneal astigmatism after surgery, but it is not involved in the surgical process.
I perform epithelial mapping with a wide-field OCT (Cirrus 6000, Carl Zeiss Meditec) to visualize where epithelial thickness is greater.
Usually, the epithelium is thicker and the stroma is thinner in the location of the scar. This allows me to compare the topography and the epithelial mapping.
I also perform a complete ocular examination with endothelial cell count, fundus, macular OCT, IOP, and optic nerve scan.
Before treatment, I explain to the patient that, although the procedure is short, the postoperative recovery period can be uncomfortable, especially in the first 2 days. This is because of the removal of the epithelium.
The patient will experience photophobia and red eye and will need to wear contact lenses for 5 days until the epithelium normalizes.
I also explain that the patient will need to use several drops, including antibiotics, corticosteroids, nonsteroidals, and artificial tears. I inform them that sometimes 1 attempt is not enough; it may be necessary to perform an enhancement, although this is rare.
It is vital that the patient understands that this is not refractive surgery on a virgin cornea. It is a procedure designed to regain visual acuity that has been lost, so it is not as easy as performing LASIK.
When I am ready to perform the procedure, the first thing I do is access the high-quality topographic images already recorded.
I introduce the central corneal thickness, select the surface ablation mode, and choose the size of the optical zone (usually 7 mm).
After integrating the images and data with the patient’s manifest refraction into the planning station, software calculates the treatment required to regularize the optical zone to a spherocylindrical shape with minimum tissue ablation. It calculates the microns at each point that it will treat.
In the transepithelial mode of the planning station software, the ablation is automatically increased to 50 µm (because the epithelium is usually 50 µm) in a uniform pattern all over the optical zone with no transition zone. There is no need for a masking agent.
Before starting treatment, I simply dry the cornea and apply an easy-to-use excimer laser (MEL 90, Carl Zeiss Meditec).
At the end, I apply mitomycin C for 1 minute on the cornea with a surgical sponge to avoid the limbus, followed by gentle washing with balanced salt solution.
When the procedure is complete, I place the contact lens (Biofinity, CooperVision) and then prescribe antibiotics and corticosteroids to avoid haze.
I also prescribe nonsteroidal anti-inflammatory drugs to control the pain in the first 2 days and artificial tears. I also advise the patient to wear sunglasses when outdoors.
The patient returns 5 days postoperatively if the epithelium is restored enough, and then I remove the contact lens. If the epithelium has not been restored, the patient waits 3 or 4 more days before returning.
I have found that younger patients’ epitheliums usually return to normal in 5 days, whereas it might take several weeks in older patients. I monitor to determine the right time to remove the contact lens.
One month postoperatively, I have the patient return and assess their IOP because of the use of topical steroids. I will allow as many postoperative visits as necessary, but the typical protocol for these visits is 24 hours, 1 week, 1 month, and 3 months.
At 3 months, I perform refraction and topography to determine whether an enhancement or correction with spectacles is required.
As a refractive surgeon, I prefer to perform an enhancement with a laser, but in some cases, older patients, for instance, I might decide to prescribe spectacles.
A 28-year-old man presented with a BCVA of 20/100. He had epidemic keratoconjunctivitis with subepithelial infiltrates. These infiltrates were extremely dense in the middle of the cornea. They were affecting the visual axis and the irregularity was very high.
After topography-guided treatment, his vision recovered to 100%. However, it is important to note that this was not an easy process for the patient. His complete recovery was not achieved until 3 months postoperatively, although he improved daily (Figures 3 and 4).
In a separate case, a 74-year-old woman presented with Salzmann nodular degeneration that was so symptomatic that her vision was 20/70 in her dominant eye. The patient had amblyopia in her good eye.
After topography-guided treatment, she had many surface complaints, which was normal at her age. Her vision is now 0.8, so we have nearly doubled her visual acuity and she is extremely happy.
I also performed the procedure on her other eye. However, we did not have much success because of amblyopia. However, she is satisfied with both procedures, especially in the dominant eye.
I encourage cataract and refractive surgeons to consider topography-guided treatment because it is easy to plan and perform. The algorithm behind the treatment is robust, and the calculation work is done for the surgeon.
Ultimately, the end result of this procedure may not be spectacle independence, given these patients’ conditions prior to surgery, but BCVA can be improved.
As a result, this proves to be a useful tool for experienced surgeons who wish to treat therapeutic cases in their practices.
Marta Ibarz Barberá, MD
Barberá is a cataract and refractive surgeon and glaucoma specialist at Oftalvist Madrid and Moncloa HLA Hospital, Madrid, Spain. She has no financial disclosures to make.