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New method of keratoconus grading to aid in planning treatment strategies
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A new function-based method of keratoconus grading takes into account patients’ subjective experiences and might lead to better planning of treatment strategies, a physician said.
“Keratoconus can be defined as a gradual degradation of quality of vision occurring over a period of time that goes from puberty to the 40s. In this span of time, patients go from excellent spectacle vision (ESV) to good spectacle vision (GSV) to bad spectacle vision (BSV) to impending corneal scarring (ICS) and then terminal keratoconus, which is the stage of legal blindness,” Waleed Al-Tuwairqi, MD, said at the World Ophthalmology Congress, in Abu Dhabi, United Arab Emirates.
The new classification takes into account the stages excluding ESV, in which minor changes may indicate subclinical keratoconus or no keratoconus at all.
“I find these four categories very useful when it comes to making decisions on the treatment approach. We now have several new treatment options, and I found that a new method of grading was needed to have a more exact correspondence between disease stages and treatment choices,” Al-Tuwairqi said.
Keratoconus stages
The GSV stage correlates with minor changes in visual function. Best corrected vision is 20/25 or better at distance and J2 at near, and coma is still below 1.5 µm at 6 mm diameter on Placido topography. Posterior elevation is 15 µm to 40 µm, maximum keratometry reading is less than 51 D, and corneal topography shows unquestionable keratoconus patterns. Patients start experiencing subjective difficulties but can still drive at night with spectacles.
Waleed Al-Tuwairqi
“At this stage, patients come because they can no longer function with the spectacles they have. They ask for a new prescription or want some counseling for refractive surgery,” Al-Tuwairqi said.
Later on, in the BSV stage, the patient becomes noticeably symptomatic, with driving at night and other daily tasks causing difficulty. Vision is still 20/30 at distance and J2 at near, but coma is high, between 2.5 µm and 5 µm, elevation is more than 40 µm, and maximum keratometry reading is elevated (50 D to 55 D). Cone dimension correlates with symptoms, but the cornea is still clear.
“Patients feel their quality of vision and quality of life are getting poor, and they are very worried about further progression,” Al-Tuwairqi said.
When the disease progresses, adhesion between anterior and posterior cornea leads to the ICS stage. Vision is 20/50 or worse at distance and J3 or worse at near. Corneal coma is more than 5 µm, posterior elevation is over 60 µm, and keratometry reading is between 55 D and 65 D. Topography shows a large cone area and striae-like changes on the cornea.
“Patients are very symptomatic and quite desperate with fear of becoming blind at this stage, but we can still propose something other than transplantation,” Al-Tuwairqi said.
Treatment options
With the new classification system as a guide, an appropriate procedure can be designed for each stage of the disease.
According to Al-Tuwairqi, patients with GSV have two choices: PRK with corneal cross-linking or toric implantable Collamer lens (STAAR Surgical) with corneal cross-linking. Both options can provide spectacle independence in most cases and halt disease progression at the same time.
“With PRK and [corneal cross-linking], I achieved emmetropia in 77% of the cases. Patient satisfaction of quality of vision was 76%. If the refractive error is high and associated with axial myopia, and if corneal thickness doesn’t allow PRK, I do ICL implantation and add [corneal cross-linking] if I suspect progression,” he explained.
At the BSV stage, Al-Tuwairqi recommends intracorneal ring implantation. The aim is neither emmetropia nor spectacle independence but to regularize the cornea and improve visual function to the level of GSV.
Intracorneal ring implantation is deemed successful when maximum keratometry drops to 46 D or is reduced by 4 D, postoperative sphere decreases by 3 D, coma is reduced by 0.83 µm, near vision is 20/40 or better, and five lines of uncorrected vision or 2.3 lines of best corrected vision are gained, according to Al-Tuwairqi.
“In more than 100 eyes, I had 82% of patients who said they were satisfied,” he said.
The tunnels should be constructed with a femtosecond laser, and smaller rings (5 mm) offer better results, he said. If he adds PRK, he performs it 6 months to 9 months after intracorneal ring implantation if stable refraction is achieved and only if patients are satisfied with the results of intracorneal ring implantation. A corneal thickness of at least 450 µm is required.
“I do a light PRK, 30 µm to 50 µm deep, aimed at correcting three lines, and I call it ‘two-step treatment,’” he said.
At the stage of ICS, Al-Tuwairqi implants a MyoRing (Dioptex) to stretch and regularize the cornea. The aim is mainly to prevent or delay the need for graft surgery. In his hands, a mean gain of 2.7 lines of uncorrected vision and 1.7 lines of corrected vision was achieved, and patient satisfaction was 65%.
Another potential treatment at this stage is stromal transplantation, but the results of this technique are still preliminary and controversial.
“We cut an 8.5-mm disc of donor tissue from which the epithelium and Bowman’s are removed. The disc is implanted into a 9-mm pocket in the recipient, through a 4.5-mm incision. I performed stromal transplantation in two cases. The cornea was regularized, but visual results were not very impressive,” Al-Tuwairqi said.
At the stage of corneal scarring, corneal grafting is the only option.
In the ESV stage, when the diagnosis of keratoconus is still questionable, PRK with corneal cross-linking or Lasik Xtra (Avedro) can be performed, Al-Tuwairqi said.
“Lasik Xtra is a new procedure in which, following femto-LASIK, an accelerated [corneal cross-linking] procedure is performed under the thin, 90-µm LASIK flap,” he said. “The stroma is soaked with riboflavin for 1.5 minutes and exposed to ultraviolet irradiation for a further 1.5 minutes. My results in 10 patients are preliminary but encouraging.” – by Michela Cimberle