Vault vs Staining
Lynette Johns OD FAAO FSLS
Corneal vault is a very important topic in scleral lens fitting. Large diameter scleral lenses that rest solely on the sclera typically vault the cornea and bear their weight on the conjunctiva overlying the sclera. There is debate among experts about what constitutes optimal vault. If there is significant corneal contact, staining is likely to occur. It is crucial to carefully inspect the cornea after removing a scleral lens to ensure that there was no significant corneal contact.
A 38-year-old male returned to the office for his annual scleral lens evaluation. He had a history of keratoconus OU. The right eye had hydrops, and the left eye had a 7-year-old corneal transplant. He reported wearing both lenses for 15 uninterrupted hours with excellent comfort and had been wearing scleral lenses for the prior three years. Entering visual acuity was 20/30+2 OD and 20/25+1 OS.
Figure 1 shows a series of optical sections nasally (left) to temporally (right) of the left grafted cornea wearing a scleral lens. In the middle two images, the back surface of the lens is touching the corneal surface. The patient was further questioned about his overall comfort toward the end of the day. He stated that he was comfortable during his wearing time with the scleral lens. He confirmed that the eye was irritated after the lens was removed.
Figure 2 shows an area of inferior-nasal staining of the corneal graft that is consistent with the area of scleral lens contact. A new lens was ordered with 250 mm additional sagittal depth to provide increased corneal vault and also to allow the corneal tissue to unmold.
It can be quite easy to miss corneal contact when evaluating a scleral lens fit, especially if there are small areas of corneal elevation. Practitioners should carefully identify both the front and back surfaces of the lens, and maintain visualization of the back surface for proper vault evaluation. In this case, the patient had a corneal transplant that subsequently became more ectatic inferior-nasally. This can happen if there is thinning of the host tissue that causes the grafted cornea to tilt or advance forward. Figure 3 demonstrates the difference in thickness of the host tissue relative to the corneal graft.
Corneal staining after scleral lens wear is suspicious, and one must rule out corneal contact. The corneal staining after the lens was removed corresponds to the region of corneal touch with the scleral lens. When the scleral lens is reapplied, the lens may once again vault the cornea because it has not settled. If there is uncertainty about corneal contact, the patient may have to return for a re-evaluation of the vault once the lens has fully settled. Scheduling afternoon appointments of scleral lens evaluations can ensure proper lens settling. If after the lens has settled for six or more hours it vaults the cornea, then staining should not be present.
Dr. Lynette Johns is an adjunct assistant professor and clinical attending in contact lenses at the New England College of Optometry.
She was formerly the senior optometrist at the Boston Foundation for Sight where she exclusively fit scleral lenses and managed complex corneal disease.
She is a fellow of the American Academy of Optometry and Scleral Lens Education Society as well as a member of the BCLA. She is a clinical and educational consultant to the GP and specialty soft lens division of Bausch + Lomb.