Contact Lenses

Contact Lenses

Contact lenses are worn on the eye primarily to improve vision or protect the anterior ocular surface. Soft contact lenses are slightly larger than the cornea and are manufactured from hydrogel or silicone hydrogel plastics that allow oxygen to pass through the lens to reach the cornea. Rigid contact lenses are typically smaller than the cornea and as the name suggests are produced from stiffer plastics than soft lenses. They can correct the simple refractive errors including myopia, astigmatism, hyperopia and presbyopia, along with more complex optical problems resulting from an irregular cornea (eg. keratoconus).

Scleral Contact Lenses

 

 

Scleral contact lenses are large diameter rigid lenses often used in the refractive correction of corneal ectasia or therapeutic treatment of severe dry eye. A number of studies conducted within the Contact Lens and Visual Optics Laboratory have investigated the physiological response of the eye to short-term scleral contact lens wear including; ocular tissue compression, changes in intraocular pressure and corneal optics, and corneal swelling and recovery.

 

LEFT: A miniscleral contact lens observed with sodium fluorescein during primary gaze. The superior shadow indicates a region of pseudo corneal bearing which disappears on downward gaze. RIGHT: The illuminated post-lens tear layer filled with sodium fluorescein during minisceral contact lens wear, visualised with a Scheimpflug imaging system. The thickness of the post-lens tear reservoir is greatest centrally and diminishes towards the peripheral cornea.

 

High resolution OCT images of the sclera before and after a period of miniscleral contact lens wear. The red arrows in the lower image after lens removal indicate a region of compression, primarily the conjunctiva and episcleral tissues overlying the sclera, at the contact lens landing zone.

 

Optics of Contact Lenses

The optical properties of contact lenses on the eye can be measured by using a wavefront sensor to acquire the eye’s wavefront without a contact lens (“bare eye”) and with a contact lens on the eye. The difference in wavefront between these two conditions is the optical effect of the contact lens on the eye.


Further Reading