There is some concern that spherical haptics may not rest properly on the often-toric scleral surface. Toric landing curves can help a scleral lens to align properly with the scleral surface, reducing flexure and resulting in improved vision, comfort and wearability (Visser et al, 2006).   

Case Description

A 31-year-old female previously unsuccessful GP contact lens wearer presented for scleral contact lens fitting after penetrating keratoplasty in her left eye 12 months prior. Her history is positive for bilateral keratoconus, and she is currently corrected with spectacles but unhappy with her vision. She had been prescribed one drop daily of fluoromethalone 0.1% suspension in her left eye for reduction of swelling.

Her visual acuity (VA) with spectacles was OD 20/70 and OS 20/50. Manifest refraction was -1.00 -5.00 x 087 with 20/40 OD, and -2.25 -6.75 x 116 with 20/40 OS. The right cornea showed ectasia and mild thinning with 1+ striae, while the left was clear with a compact full-thickness corneal graft. 

Trial fitting was done with the Atlantis Scleral (X-Cel) in Boston XO OD: sag 5000 (+100 central sag adjustment), 15.5 diameter, -4.25 DS power with a standard spherical limbal and scleral zone. With this lens, visual acuity was  20/20, J1+ and there was 300 µm of clearance centrally. The same diagnostic lens and material was chosen for the left eye with a sag 4800 (+100 central sag adjustment), 15.5 diameter, -3.25 DS power and standard spherical limbal and scleral zones. With this lens, visual acuity was 20/20, J1+ and there was 300 µm of clearance centrally. 

On return visit, the patient reported all-day comfort, with some variable vision and glare as the day progressed. VA was 20/20- OD and 20/25 OS with J1+ OU at near. Examination in both eyes revealed impingement along one oblique axis and slight edge left along the perpendicular meridian. Over-refraction showed 1.25D of astigmatism OD and OS corresponding to over-K values, indicating flexure. 1+ fogging of the tear reservoir was noticed OD and OS. Lenses were reordered with the same parameters but with toric haptics.  

At the second follow-up, the patient reported superb all-day comfort with much better and more consistent vision. The haptic was evenly aligned in each quadrant, and vision returned to 20/20 in both eyes and 20/15 binocularly. Over-refraction and over-keratometry showed 0.25D of astigmatism OD and OS with no debris visualized in the tear reservoir.  

Discussion

This case displayed many of the advantages of a toric landing zone. The patient showed a common pattern of flexure that increases throughout the day as the scleral lens bends around the toricity of the scleral surface. Toric landing zones allow the haptic to conform more appropriately to the curvature of the sclera, which can lead to improved VA, comfort, and wear time.   

One could argue that all scleral lenses be fit with toric landing zones and that, when indicated, designs should allow for quadrant-specific manipulation. Utilizing smaller (<17 mm) designs reduces the expected toricity and often makes fitting less complicated. That said, scleral architecture varies widely at all chord lengths, and an individualized approach must be taken to reduce complications.

REFERENCES:

1. Visser, Esther-Simone, et al. “Advantages of Toric Scleral Lenses:” Optometry and Vision Science, vol. 83, no. 4, Apr. 2006, pp. 233–36. DOI.org (Crossref), doi:10.1097/01.opx. 0000214297.38421.15.
_________

Dr. Biondo owns Kirkwood Eye Associates in St. Louis, MO. He is a Fellow of the Scleral Lens Education Society, is a consultant  to the specialty contact lens industry, and speaks internationally on specialty contact lenses and practice management.