How an impression-based lens is made
Most scleral lenses are fitted with trial lenses: your fitter places lenses of known shape on your eye, watches how they sit, and orders a lens with adjustments. An impression-based lens takes a different route. The fitter takes an impression of the front surface of your eye. That mold is scanned with a 3D scanner, and the lens is cut on a lathe to match it.[1]
Because the lens is shaped from your actual eye surface, it can follow features that standard designs struggle with, such as raised areas on the white of the eye or the bump of a glaucoma drainage device. EyePrintPRO is the best-known system.[1]
Who it’s for
Impression-based lenses are usually a second-line option. In a review of 44 patients (70 eyes) at three specialty practices, 29 patients had already tried standard scleral lenses without success.[2] In a single-center study of 95 eyes, reasons for wear included irregular corneas, ocular surface disease, exposure of the cornea, neurotrophic keratitis, and features beyond the cornea, such as glaucoma drainage devices, that prevented a standard lens from fitting.[3]
They’re also not common. In a survey of 423 practitioners who fit scleral lenses for keratoconus, those who had impression-based technology used it for a median of 8% of their fits, and most fits overall were done with trial lenses.[5]
What the studies show
All of the published studies are small and look back at patient records.
- Vision. Vision improved significantly compared with patients’ previous correction in the multicenter review.[2] In the 95-eye study, median vision improved from about 20/94 to about 20/24.[3] A smaller study of 14 eyes found average vision improved from 20/36 to 20/21.[4]
- Fit. In the multicenter review, ideal alignment on the white of the eye was achieved in 74% of fits and complete clearance of the limbus in 83%. Completing the fitting took an average of 4 visits.[2]
- After failed scleral lenses. Of 56 eyes that had previously failed standard scleral lenses, 49 continued wearing impression-based lenses.[3]
- Efficiency. Practitioners surveyed reported a median of 15 minutes to take impressions, and said the first impression was adequate to order a lens a median of 90% of the time. The time for the first visit and the number of lenses ordered were similar across trial-lens, scan-based, and impression-based fitting.[6]
Impression-based lenses can also be combined with advanced optics. One case report described adding wavefront-guided optics to an impression-based lens for a man with keratoconus, improving his vision by two lines in each eye.[7] See wavefront-guided scleral lenses.
Where they fall short
Impression-based lenses don’t remove the usual challenges of scleral lens wear. In the 95-eye study, one third of eyes (33.1%) developed adverse symptoms during wear and 16% developed adverse signs. Lens wear stopped in 10.5% of eyes, and 14.7% needed a new impression and lens.[3] Two eyes in the multicenter review stopped wearing because of complications.[2]
Not every practice has the equipment to offer them, which can mean travel. If standard lenses haven’t worked, other routes include a refit with a toric or custom landing zone, a profilometry-guided design, or PROSE. For more on next steps, see what if scleral lenses don’t work for me?
Common questions
Does taking the impression hurt?
Ask your fitter what to expect and whether they use numbing drops. A soft, putty-like material is used to take a mold of the front of your eye. If you're anxious about it, say so beforehand so they can talk you through each step.
Is an impression-based lens better than a regular scleral lens?
Not for everyone. Most people are fitted successfully with standard scleral lenses chosen from trial lenses. Impression-based lenses are mainly used when the eye's surface is too irregular for a standard design, or when standard lenses haven't worked.
Will I need more than one impression?
Sometimes. In one study, about one in seven eyes needed the lens remade from a new impression. Your fitter will tell you if the first lens needs adjusting or a new mold.