Surgical vision correction techniques (including LASIK and PRK) are done at the surface of the eye. Intraocular techniques
as the name implies
are done within the eye. Two intraocular techniques hold promise: phakic intraocular lenses and clear lens extraction.
Intraocular techniques are derived from cataract surgery. (Cataracts are opacities in the crystalline lens that usually occur with age.) In modern cataract surgery
the crystalline lens is removed and replaced with a clear artificial lens called an Intraocular Lens (IOL). Many millions of cataract procedures are done every year around the world
so the technique has been greatly refined. Most ophthalmologists are skilled in cataract removal and IOL implantation.
the crystalline lens was removed only when cataracts were present. Then some surgeons realized that the crystalline lens could be removed and replaced with an IOL as a way to correct refractive errors in eyes without cataracts. This technique is called Clear Lens Extraction (CLE). The term “clear lens” applies because the crystalline lens that is removed has no opaque cataracts in it.
CLE is being studied in cases of very high degrees of myopia
where LASIK and PRK are less effective. (PRK is effective with low and moderate myopia. LASIK is effective with low
and high myopia. But neither LASIK nor PRK is optimum for extreme myopia.)
The phakic IOL technique is similar to clear lens extraction in that an artificial lens is implanted in the eye. However
with a phakic IOL
the patient s crystalline lens is not removed. (The Greek word phakos means “lens”; and a person who has a crystal-line lens is said to be “phakic”; a person whose crystalline lens has been removed
usually due to cataracts
is said to be “aphakic.”) In the phakic IOL procedure
an IOL is implanted just in front of the crystalline lens. (One company refers to its phakic IOL as an “implantable contact lens.”)
The advantage of the phakic IOL is that
in younger patients
the crystalline lens remains
and the patient doesn t lose the ability to accommodate. Because the crystalline lens is required for accommodation
which removes the lens
will end the patient s ability to accommodate.
Both CLE and phakic IOLs hold promise for patients with extreme refractive errors. LASIK and PRK
the standard treatments for the vast majority of refractive errors
are less effective for extreme refractive errors. For the great bulk of refractive errors
laser vision correction is more precise than CLE or phakic IOL implantation. Laser vision correction is also safer
and far less invasive. To some degree
phakic IOL implantation is a reversible technique. CLE
definitely isn t. Once the crystalline lens is removed
nothing can replace it.
As good as phakic IOLs and CLE promise to be
their usefulness is likely to be limited to treating extreme refractive errors.