Intrastromal Corneal Inlays
Intrastroma Corneal inlays for Presbyopia treatment
Corneal inlays are special type of devices that are implanted in the cornea for correction of near vision in patient with presbyopia. This implant is inserted in the corneal stroma or corneal flaps with the aid of femtosecond laser or even microkeratome.
What are the types of corneal Inlay?
Small aperture inlays
These inlays are ring shaped with central central aperture and they are opaque. The opaque ring blocks the peripheral light rays while the central aperture allows the central light rays to pass through. It helps to improve the near vision and improve the depth of focus.
An example of small aperture inlays is Kamra Inlay by AcuFocus. It was approved by FDA to improve near vision in patients with presbyopia. It is an opaque ring shaped and it is made of made of polyvinylidine difluoride and it is pigmented with carbon nano-particles.
There are over 8400 laser etched holes in the body of the ring to facilitate diffusion and movement of oxygen, aqueous and nutrients through the cornea.
Corneal reshaping inlay
This type of corneal inlay improves near vision in presbyopic patients by changing the curvature of the anterior surface of the cornea. This inlay is transparent and its central part is thicker than the peripheral. The slightly change in the curvature of the central part of the anterior cornea increases the refractive power of the central part of the cornea, thus improve the near vision.
An example of this inlay is Raindrop inlay from ReVision Optics. This inlay is thin transparent implant that allows the transmission of nutrition and oxygen through it. It has no refractive power because its refractive index is the same as that for the cornea.
Raindrop inlay was approved by FDA in 2016; however, it was recalled in October of 2018 secondary to post-operative corneal haze. Nevertheless, it was recall from the market on 2018 because they found more than 75% of patients developed corneal haze from the implant.
Refractive corneal inlay
This type of inlay has refractive power and helps to improve near vision for presbyopic patient. An example of this type is The Presbia Flexivue Microlens from Presbia. This device has central hole to allow the movement of oxygen and nutrition through the cornea.
The hole is surrounded by plano optical zone that has no refractive power and allows distance light rays to pass through it without any change and focus on the retina thus the distance vision is not affected. The peripheral optical zone has refractive power to refract light ray from the near object to the retina and improve the near vision.
Indications of Corneal Inlay
1- Presbyopic patient.
2- Age between 40-60.
3- Implant in the non dominant eye.
4- Phakic patients with no cataract.
5- Can be used in patients with myopia, hyperopia and astigmatism when it is combined with lasik surgery.
Contraindications of intrastromal Inlay
2- No corneal ectasia or keratoconus.
3- Minimum corneal thickness of 300 microns.
4- Chronic ocular inflammation and uveitis.
5- Active corneal infection.
6- Uncontrolled Glaucoma.
Side effects and Complications of corneal inlay
1- Disturbance of night vision with glare and halos around light.
2- Decrease in contrast sensitivity.
3- Dry eyes.
4- Corneal haze with or without epithelial ingrowth.
5- Reduction in monocular distance vision in the eye with implanted inlay.
6- Decentration of the implant which can affect both near and far vision.