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What Are Corneal Inlays?

A corneal inlay is a tiny, engineered device that was surgically implanted within the cornea of one eye, typically the non-dominant eye, to correct presbyopia, the age-related decline in near vision. These devices are significantly smaller than the width of a standard eraser tip and were designed to change the refractive properties of the cornea to increase the eye's depth of focus. The procedure involved an ophthalmologist using a laser to create a small flap or pocket in the mid-cornea, where the inlay would be placed during a brief, outpatient surgery lasting about 10 to 15 minutes.

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What Are Corneal Inlays?

A corneal inlay is a tiny, engineered device that was surgically implanted within the cornea of one eye, typically the non-dominant eye, to correct presbyopia, the age-related decline in near vision. These devices are significantly smaller than the width of a standard eraser tip and were designed to change the refractive properties of the cornea to increase the eye's depth of focus. The procedure involved an ophthalmologist using a laser to create a small flap or pocket in the mid-cornea, where the inlay would be placed during a brief, outpatient surgery lasting about 10 to 15 minutes.

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What Was The Purpose Of Corneal Inlays?

The primary purpose of corneal inlays was to reduce or eliminate the reliance on reading glasses in middle-aged individuals suffering from presbyopia. By altering how light entered the eye, the implant corrected the close-up focus while attempting to preserve distance vision in the treated eye. Clinical comparisons showed that patients receiving corneal inlays often achieved better outcomes in near and distance visual acuity and binocular depth perception (stereopsis) compared to patients who received traditional monovision LASIK corrections.

However, corneal inlays are now generally considered a historical option. Although the implants were once seen as a promising way to avoid reading glasses, safety concerns arose over time, leading to them being withdrawn from the market or no longer produced. The procedure required careful patient selection, typically targeting those between 45 and 55 years old who had good distance vision but were struggling with near vision.

What Are The Different Types Of Corneal Inlays?

Corneal inlays utilized three distinct mechanisms to improve near vision. The small aperture inlay, exemplified by the KAMRA device, functioned like a camera's aperture, or f-stop. This ring-shaped, opaque implant had a central pinhole that increased the depth of field by allowing only central light rays to enter the eye, minimizing refractive errors from the periphery.

Other inlays focused on altering the corneal structure itself. Corneal reshaping inlays, such as the Raindrop Near Vision Inlay, improved close vision by creating a localized increase in the curvature of the central cornea. This transparent hydrogel implant allowed near light rays to focus through the central curved portion while distance vision light rays passed through the flatter peripheral cornea. A third type, the refractive corneal inlay (e.g., Presbia Flexivue Microlens), used surrounding concentric rings of progressively increasing power to focus light from near and intermediate objects onto the retina, while a central plano zone maintained distance focus.

What Were The Safety Concerns Surrounding Corneal Inlays?

Safety concerns surrounding corneal inlays led to their decline in use and subsequent removal from the market. The KAMRA inlay, for example, raised issues including poor night vision, difficulty seeing in dim light, and visual disturbances like halos, streaks, or double vision in some patients. It was also found that these inlays were "not easy to deal with" post-implantation, requiring the long-term use of topical steroid drops for three to four months to prevent complications, which sometimes induced early cataracts or accelerated presbyopia progression.

The Raindrop Near Vision Inlay was also removed from distribution in the United States after a post-approval study indicated potential complications. Complications for inlays generally included corneal haze, loss of contrast sensitivity, optical aberrations, and chronic dry eye issues, highlighting the importance of meticulous surgical technique and careful patient selection.

When Were Corneal Inlays Considered Successful?

Corneal inlays were considered successful when they allowed the patient to achieve sufficient near vision to reduce or eliminate dependence on reading glasses while maintaining good distance vision. In one study, 79% of inlay patients reported satisfaction with their near vision, and 86% were satisfied with their distance vision, with better overall outcomes than monovision LASIK patients.

Success was also measured by stability and safety over time, specifically limiting the loss of the best-corrected distance visual acuity (CDVA). While both FDA-approved devices demonstrated generally safe profiles in trials, the long-term goal was to ensure patients did not experience a significant or permanent decline in their overall quality of vision, which ultimately proved challenging, leading to the devices' discontinuation or recall.

Frequently Asked Questions

What Are The Potential Side Effects?

The side effects associated with corneal inlays were primarily visual and structural. Visual complications included reduced visual acuity, difficulty reading in dim light, and a loss of contrast sensitivity. Patients also reported optical aberrations, which are visual quality issues like halos or glare, especially at night.

Structural side effects involved corneal haze (clouding of the cornea), dry eye symptoms, and potential issues related to the inlay's position, sometimes resulting in corneal scarring. In some cases, these complications necessitated the surgical removal, or explantation, of the inlay to restore the cornea to its pre-surgical state, though explantation often resulted in improved visual acuity.

Why Are Corneal Inlays No Longer Used In The U.S. Market?

Corneal inlays are generally no longer used or manufactured because long-term follow-up raised safety concerns regarding potential vision problems, complications, and the need for frequent post-operative steroid use.

What Common Visual Problem Were Corneal Inlays Designed To Correct?

Corneal inlays were designed specifically to correct presbyopia, the age-related condition that causes near vision to decline, making it difficult to read or focus on close objects.

What Was The Minimal Required Corneal Thickness For An Inlay Procedure?

Corneal thickness requirements were stringent, with patients needing a minimum Central Corneal Thickness (CCT) of 500 micrometers (?m) to be eligible for the surgery.

References

American Academy of Ophthalmology (AAO), Corneal Inlays: Surgical Correction of Presbyopia, https://www.aao.org/education/current-insight/corneal-inlays-surgical-correction-of-presbyopia

American Academy of Ophthalmology (AAO), Corneal Inlays: Alternative to Reading Glasses, https://www.aao.org/eye-health/treatments/corneal-inlays-alternative-to-reading-glasses

National Institute for Health and Care Excellence (NICE), Corneal inlays for correcting presbyopia, https://www.nice.org.uk/guidance/ipg455/evidence/overview-pdf-483729373

ResearchGate, Corneal Inlays Complications, https://www.researchgate.net/publication/396927013_Corneal_Inlays_Complications

NIH National Library of Medicine - PMC, Overall Safety and Efficacy of the KAMRA and Raindrop Inlays, https://pmc.ncbi.nlm.nih.gov/articles/PMC5596232/

American Academy of Ophthalmology (AAO), FDA Alert: Raindrop Near Vision Inlay May Raise Risks, https://www.aao.org/headline/fda-alert-raindrop-near-vision-inlay-may-raise-ris

NIH National Library of Medicine - PubMed, Corneal Inlays vs. Monovision LASIK: Patient Outcomes, https://pubmed.ncbi.nlm.nih.gov/29033538/

NIH National Library of Medicine - PMC, Safety and Patient Satisfaction with the KAMRA Corneal Inlay, https://pmc.ncbi.nlm.nih.gov/articles/PMC5098597/

References