In ophthalmology, the term “phakic” refers to an eye that still possesses its natural crystalline lens. This term originates from the Greek word “phakos,” which means lens or lentil. Understanding “phakic” is important because the natural lens plays a central role in how we see the world clearly.
The Function of the Natural Lens
The eye’s natural lens is a transparent, flexible structure located behind the iris. Its primary function involves bending and focusing incoming light rays precisely onto the retina, the light-sensitive tissue at the back of the eye. This process is similar to how a camera’s lens adjusts to create a sharp image on film or a digital sensor. The lens achieves this focus by changing its shape, a process known as accommodation, allowing the eye to shift focus between distant and near objects. Ciliary muscles surrounding the lens contract or relax, altering its curvature to ensure light converges correctly on the retina for clear vision at various distances.
Aphakia and Pseudophakia
Aphakia describes an eye that lacks its natural crystalline lens, leading to significantly blurred vision due to the eye’s inability to properly focus light. While rare, some individuals are born without a lens, or it can be lost due to severe eye trauma. The most common reason for aphakia, however, is the surgical removal of a cataract without replacing the lens.
Pseudophakia, a much more common condition, refers to an eye where the natural lens has been removed and replaced with an artificial intraocular lens (IOL). This procedure is primarily performed during cataract surgery, where the clouded natural lens is exchanged for a clear synthetic one. The implanted IOL then takes over the focusing function, restoring vision that was obscured by the cataract. These artificial lenses are designed to be permanent, providing a long-term solution for vision correction after the original lens is no longer functional.
Phakic Intraocular Lenses
Phakic Intraocular Lenses (PIOLs), also known as implantable collamer lenses (ICLs), are artificial lenses implanted into the eye to correct refractive errors, such as nearsightedness or farsightedness, without removing the eye’s natural crystalline lens. Phakic IOLs are typically made of biocompatible materials like collamer, plastic, or silicone, ensuring they can safely remain inside the eye.
The procedure involves making a small incision in the cornea and carefully positioning the PIOL either in front of or behind the iris, in cooperation with the natural lens. This differs from LASIK, which reshapes the cornea, and cataract surgery, which replaces the natural lens entirely.
Phakic IOLs are often an option for individuals with high degrees of refractive error or thin corneas who may not be suitable candidates for laser vision correction like LASIK. They offer an additional focusing element, working alongside the eye’s existing structures to provide clear vision.