Benefits of topography-guided treatments for irregular corneas

Ophthalmology Times Europe Journal, Ophthalmology Times Europe May 2021, Volume 17, Issue 4

Topography-guided treatments for irregular corneas can improve patients’ best corrected visual acuity. The technique is easy to plan and perform, 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 who have this refractive issue can be candidates for customised 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 as to what the outcomes will be. 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 or not 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 provides a great opportunity for patients who have visual complaints that are caused by corneal irregularities.Topography-guided treatment not only allows restoration of the cornea but can also soften the irregularity of the cornea and produce good refractive results.

Patient evaluation
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; best corrected visual acuity (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 fibre layer and ganglion cells.

I integrate topographic images and data from two anterior topographic screening tools (Atlas 9000, Zeiss and Pentacam, Oculus). We integrate the topographies obtained with the Atlas 9000 into the planning station (CRS Master, Zeiss; Figure 2) and use the Pentacam to analyse the evolution of the corneal shape—specifically changes in total corneal astigmatism after surgery—but it is not involved in the surgical process.

Next, I perform epithelial mapping with wide field optical coherence tomography (OCT; Cirrus 6000, Zeiss) to visualise where epithelial thickness is greater: usually the epithelium is thicker and the stroma thinner in the location of the scar. This allows me to contrast 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.

Treatment protocol
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 due to 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 normalises.

I also explain that the patient will need to use several drops, including antibiotics, corticosteroids, nonsteroidals and artificial tears, and I inform them that sometimes one 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. We introduce the central corneal thickness, select surface ablation mode and choose the size of the optical zone (usually 7 mm).

After integrating all the images and data with the manifest refraction of the patient into the planning station, the software calculates the treatment required to regularise the optical zone to a spherocylindrical shape with minimum tissue ablation. It calculates the microns at each point that it is going to treat.

Treatment pearls
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 the laser (MEL 90, Zeiss). It is easy to use. At the end, mitomycin C is applied 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, nonsteroidal anti-inflammatory drugs to control the pain in the first 2 days, and artificial tears. We 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, then the patient waits 3 or 4 days longer before returning.

We have found that younger patients’ epitheliums usually return to normal in 5 days whereas it might take several weeks in older patients. We monitor to determine the right time to remove the contact lens.

One month postoperatively, we have the patient return and assess their IOP, due to the use of topical steroids. We allow as many postoperative visits as necessary, but the typical protocol is 24 hours, 1 week, 1 month and 3 months.

At 3 months, we perform refraction and topography to determine whether an enhancement or correction with spectacles is required. As refractive surgeons, we prefer to perform an enhancement with the laser, but in some cases (older patients, for instance) we might decide to prescribe spectacles.

Case studies
A 28-year-old man presented with a BCVA of 20/100. He had epidemic keratoconjunctivitis with subepithelial infiltrates. However, 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. She 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.

We also performed the procedure on her other eye; however, we did not have much success due to the amblyopia. However, she is happy with both procedures, especially in the dominant eye.

Conclusion
I encourage cataract and refractive surgeons to consider this technique because it is easy to plan and perform. The algorithm behind the treatment is robust and the calculation work is done for the surgeon.

The end result of this procedure may not be spectacle independence, given these patients’ conditions, but BCVA can be improved. This is a useful tool for experienced surgeons who wish to treat therapeutic cases in their own practices.

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Marta Ibarz Barberá, MD
E: marta@martaibarz.com
Dr Marta Ibarz 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.