Cornea & Ocular Surface

Study: Scleral Lenses Associated With Corneal Edema After Penetrating Keratoplasty

Avatar photoMary Stroka
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TRUJILLO, PERU – APRIL 20: A surgeon works on the eye of Reis-Buckler syndrome patient Diana, aged 17, during surgery onboard the Orbis Flying Eye Hospital on April 20, 2018 in Trujillo, Peru. Reis-Buckler corneal dystrophy is a rare genetic condition which causes the Bowman’s layer of the cornea to disintegrate. Diana’s mother Rosa has the same syndrome and has struggled with sight loss since the age of nine. After suffering with the condition since the age of three, Diana was chosen for a penetrating keratoplasty procedure (cornea transplant) during a programme run by Orbis, the ophthalmic training organisation. Founded in 1982 by ophthalmologist David Paton, Orbis trains eyecare teams across Africa, Asia and Latin America to improve the standard of eyecare in the region. As well as working in local hospitals, the charity also has a self-sufficient surgical unit on the Orbis Flying Eye Hospital, a converted McDonald-Douglas MD10 aircraft. (Photo by Leon Neal/Getty Images)
Researchers compared the central corneal response to short-term scleral lens wear in subjects after penetrating keratoplasty with those who did not undergo the procedure.

Scleral lens wearers who previously underwent penetrating keratoplasty (PK) exhibited approximately 3 times more macular edema, and 2.5 times more variability in central corneal response, than those who have healthy eyes in a recent study.1

While research has indicated corneal complications may be associated with scleral lens wear in patients who undergo PK, this is the first study of the central corneal response to short-term scleral lens wear, the investigators said.

“Theoretically, scleral lenses are an ideal refractive correction for the post-graft eye because they can correct a high degree of irregular corneal astigmatism,” the researchers explained. “Scleral lenses are also extremely stable compared with smaller diameter corneal rigid lenses and, if fitted appropriately, will vault the cornea entirely including the graft-host junction, reducing the potential for mechanical irritation and tissue inflammation during lens wear.”

In this study, researchers reviewed 9 post PK eyes of 9 subjects fit with oxygen-permeable nonfenestrated scleral lenses.1 They measured the corneal thickness, and compared the corneal edema and its variability with measurements from 15 scleral lens wearers with healthy corneas whose data was collected in an earlier study.2 Corneal edema was quantified across the central 6 mm. The median age of the study group was 32 (95% confidence interval (CI) 26 years old to 38 years old) and median age of the control group was 22 (95% CI, 20 years old to 24 years old).1

The researchers found that corneal thickness in the study group increased by 2.99 (95% CI, 1.13 to 4.85%) averaged across the central 6 mm (F9,1 = 13.72, P =.006), and there tended to be more edema further from the center of the cornea.1 Nine randomly selected eyes from the control group, alternately, had a mean SD corneal swelling of 0.89 (95% CI, 0.16 % to 1.62%) across the central 6 mm.1

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The subjects in the healthy control group experienced less corneal swelling (0.88% [95% CI, 0.20 to 1.56%], F15,1 = 7.97, P =.01), and the corneal edema was about the same throughout the eye, with no main effect of region (F15,5 = 0.72, P =.61), zone (F15,7 = 0.68, P =.69), or a region by zone interaction (F15,35 = 0.60, P =.97).1

The scleral lenses in this investigation were made of roflufocon D (oxygen permeability, 100 Dk; center thickness, 250 μm) with standard symmetric landing zone design that provide approximately 250 to 300 μm of central corneal clearance. They measured central corneal thickness before and immediately after they wore the lenses for a period of at least 4 hours (mean wearing time, 6.2 hours [95% CI, 5.2 hours to 7.2 hours]; range, 4 hours to 8.5 hours).1

The healthy control group wore nonfenestrated lenses made of hexafocon (oxygen permeability, 100 Dk; center thickness, 300 μm; diameter, 16.5 mm) for an average of 8.5 hours (95% CI, 8.4 to 8.6 hours; range, 8.3 to 8.8 hours).1 The lenses had an initial central clearance of 353 μm (95% CI, 287 to 419 μm).1

Limitations of the study included a small sample size, possible landing zone misalignment and other uncontrolled differences between the two groups, the researchers said. They also noted that measuring the endothelial cell density would have provided more detail regarding the corneal response after scleral lens wear.1

“Practitioners should aim to minimize any potential hypoxic and mechanical corneal stress when fitting post–penetrating keratoplasty eyes with scleral lenses,” the researchers said. “This may be achieved by increasing the scleral lens material’s oxygen permeability (however, minimal benefits are seen in healthy eyes increasing beyond 100 Dk), minimizing lens thickness (although this is influenced by the required back vertex power and can increase lens flexure), and reducing the thickness of the post-lens fluid reservoir.”

Reducing the amount of time patients wear scleral lens and using fenestrated scleral lenses may also reduce corneal edema, they said.1

Reference

1. Kumar M, Shetty R, Khamar P, Vincent SJ. Scleral Lens–Induced Corneal Edema after Penetrating Keratoplasty. Optom Vis Sci. 2020;97:697–702. doi:10.1097/OPX.0000000000001571

2. Vincent SJ, Alonso-Caneiro D, Collins MJ, et al. Hypoxic Corneal Changes Following Eight Hours of Scleral Contact Lens Wear. Optom Vis Sci. 2016;93:293–9. doi: 10.1097/OPX.0000000000000803

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