A corneal inlay (also called an intracorneal implant) is a device which is surgically implanted in the

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...

of the eye as a treatment for

presbyopia Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long sig ...

. Successful installation results in reducing dependence on

reading glasses A corrective lens is a lens (i.e. a transmissive optical device) that is typically worn in front of the eye to improve daily vision. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasse ...

, so that the user can more easily engage in everyday tasks such as using a

mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive telephone call, calls over a radio freq ...

, reading store shelf prices and working on a computer. Corneal inlays are small, thin, and permeable. Typically one is implanted in the non-dominant eye.

Jose Barraquer José Ignacio Barraquer Moner (24 January 1916 – 13 February 1998) was a Spanish ophthalmologist and inventor born in Barcelona who did most of his life's work in Bogotá, Colombia. His original pioneering investigations on corneal transpla ...

created the first corneal inlay prototype in 1949 in

Barcelona Barcelona ( , , ) is a city on the coast of northeastern Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second most populous municipality of Spain. With a population of 1.6 million within ...

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' ( Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...

. The

flint glass Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refracti ...

material which he used, however, was found to be unsuitable because of biocompatibility issues.Whitman, Jeffrey
"Corneal inlays provide safe, reversible option for presbyopia treatment."
''Ocular Surgery News U.S. Edition'' 2012 Aug. Other transparent, permeable materials were tested, including hydrogel polymers in the 1960s. Some early corneal inlay recipients experienced complications, such as

corneal opacification The human cornea is a transparent membrane which allows light to pass through it. The word corneal opacification literally means loss of normal transparency of cornea. The term corneal opacity is used particularly for the loss of transparency of ...

, thinning and melting. Researchers soon found that, as well as the material, the thickness of the inlay and the depth at which it was implanted were important, as well as permeability and centration. There was a delay in the general introduction of the treatment while considerable research was done to find safe and reliable combinations of these factors. The US

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...

approved the KAMRA corneal inlay in April 2015. The inlays are in commercial use in US, some countries in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

Asia-Pacific Asia-Pacific (APAC) is the part of the world near the western Pacific Ocean. The Asia-Pacific region varies in area depending on context, but it generally includes East Asia, Russian Far East, South Asia, Southeast Asia, Australia and Pacific Isla ...

, the Americas and the

Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...

. The inlays are implanted into the cornea either in a laser-created corneal pocket or lamellar corneal flap (similar to

LASIK LASIK or Lasik (''laser-assisted in situ keratomileusis''), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, sinc ...

). The inlays can be removed should the patient develop another condition requiring medical treatment.

Types

By 2020, there are five corneal inlays in use and under development:

KAMRA

The KAMRAinlay (AcuFocus, Inc.) is a biocompatible ring that increases the visual

depth of field The depth of field (DOF) is the distance between the nearest and the furthest objects that are in acceptably sharp focus in an image captured with a camera. Factors affecting depth of field For cameras that can only focus on one object di ...

using the physical principle of a small

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...

. This design only allows focused light to enter the eye resulting in an improvement in near and intermediate vision while maintaining distance vision. The KAMRA is the first small aperture corneal inlay approved by the US

FlexivueMicrolens

The FlexivueMicrolens (PresbiaCoöperatief U.A.) is a refractive hydrophilic

polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...

lens. The central zone of the lens is free of refractive power and the peripheral zone has a standard positive refractive power. This inlay works on a similar principle to bifocal glasses. The bifocal design provides two images to the retina simultaneously. Each specific point of focus is delivered as both a sharp and a blurred image. The FlexivueMicrolens is available in a variety of powers, and can be exchanged as presbyopia progresses.

Raindrop

The Raindrop Near Vision Inlay, formerly known as the PresbyLens or Vue+ lens (ReVision Optics, Inc) is a thin transparent biocompatible hydrogel implant. It is 2 mm in diameter and varies in thickness from 10 microns in the periphery to ~30 microns in the center. It is implanted under a

femtosecond laser Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12 s) or femtoseconds (10−15 s). A laser operated in this way is sometimes r ...

flap onto the stromal bed of the cornea, centered over a light-constricted

pupil The pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black ...

. The Raindrop Near Vision Inlay reshapes the central region of the cornea to provide a zone of increased power for focusing on near objects.

Icolens

The Icolens System (Neoptics AG) is another refractive hydrophilic polymer lens, similar to the Flexivue Microlens, with no power in the center and the peripheral zone has positive refractive power. This inlay is also available in assorted powers, which may be exchanged as required due to the progression of presbyopia.

Diffractive Corneal Inlay

The Diffractive Corneal Inlay is a novel type of corneal implant for the treatment of presbyopia, which based on the diffraction phenomena. It was developed by de Diffractive Optics Group (DiOG, Spain) and its working principle combines the

pinhole A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...

and photon sieve effects. Using diffraction, the inlay is able to generate a diffractive focus in near vision. There are several scientific studies that compare the optical properties of Diffractive Corneal Inlay with the Kamra Inlay, demonstrating that the former obtains a better performance in near vision.

References

{{Eye procedures Eye procedures