Intraocular Refractive Surgery
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Background
Disorders that require glasses or contacts (e.g. nearsightedness) may be addressed by vision correction surgery. By definition, intraocular refractive surgery is performed inside the eye as opposed to on the cornea. Two types of intraocular refractive surgery are described below: phakic intraocular lens and refractive lens exchange (clear lens extraction).
Concept
It is important to note that intraocular refractive surgery is an option for the treatment of refractive errors in healthy eyes. Conditions such as macular degeneration or glaucoma may preclude this vision correction option. Refractive errors are defined below.
- Myopia - Nearsightedness; parallel light rays focus in front of the retina, making distant objects blurry.
- Hyperopia - Farsightedness; parallel light rays focus behind the retina, making near objects blurry.
- Astigmatism - Steeper meridians in a cornea or lens that bend light more strongly, preventing a single point of focus.
- Presbyopia - Age-related decrease in focusing power of eye's natural lens, often making near objects blurry.
Currently in the United States, phakic intraocular lenses are only available to treat myopia. Refractive lens exchange is most commonly used to treat significant hyperopia in patients with presbyopia.
Diagnosis
The need for glasses or contacts is clear evidence that a form of refractive error is present.
History
Many times, intolerance of contact lenses or job requirements for uncorrected vision warrant evaluation for vision correction. Some people are not candidates cornea procedures (e.g. LASIK or laser in situ keratomileusis) due to dry eye disease, thin corneal tissue, extreme levels of near- or farsightedness, or early cataracts (dysfunctional lens syndrome). It is under these circumstances that intraocular refractive procedures are often considered.
Physical examination
Routinely, best corrected vision is determined along with eye pressure and neurological function. A thorough examination of the front and back of the eye is necessary to determine candidacy.
Diagnostic procedures
Determination of corneal thickness, pupil size, anterior chamber depth, and corneal endothelial cell count are advised. Eye length/dimensions as well as the shape and power of the cornea are calculated. White-to-white or sulcus-to-sulcus measurements are needed for the Visian ICL. This may be obtained with calipers, biometry, or topography/Pentacam (white-to-white measurements), or with ultrasound biomicroscopy (sulcus-to-sulcus measurements).
Management
Surgery
Phakic intraocular lens surgery involves placement of an artificial lens inside the eye without disturbing the eye's natural lens. Older models of the Visian ICL required peripheral iridotomies. The EVO model of the Visian ICL (FDA approved in 2022) has a central hole in the implant which precludes the need for peripheral iridotomies.[1] Viscoelastic is used to fill the anterior chamber to create room for lens insertion. Lens insertion follows with an injection apparatus or forceps. The phakic intraocular lens is then either affixed in front of the iris (e.g. Verisyse) or placed behind it (e.g. Visian ICL), depending on the model used. The viscoelastic is removed manually with balanced salt solution on a cannula. The procedure is performed one eye at a time and may be done sequentially on the same day. Sutures are to close the Verisyse incision but are not routinely required for the Visian ICL procedure. There is routinely minimal discomfort. Steroid and antibiotic drops are prescribed postoperatively.
Refractive lens exchange surgery is simply cataract surgery with intraocular lens (IOL) placement prior to the formation of a visually-significant cataract. This option corrects the refractive error as well as eliminates the formation of cataract in the future. The IOL may be a monofocal for distance or near target, or may be a multifocal or extended depth-of-focus IOL.
Surgical follow up
Intraocular refractive surgery does require follow up with a qualified doctor. One possible follow up schedule could be: the day after surgery, one week after surgery, and one month after surgery. Annual checks are advisable after most intraocular surgery.
Infection, inflammation, glaucoma, endothelial cell loss, iris abnormalities and retinal detachment have been associated with phakic intraocular lenses and as such, and endothelial cell count, intra-ocular pressure measurement and a dilated fundus exam may be indicated during follow-up examinations.
Prognosis
FDA trials for currently available phakic intraocular lenses (spherical correction of nearsightedness) have shown that better than 80% of patients saw 20/40 or better without correction. Ongoing monitoring has shown acceptably low incidence of endothelial cell loss, cataract formation, secondary glaucoma (pupillary block, pigment dispersion), iris atrophy (pupil ovalization), and traumatic dislocation. At least annual eye examinations are recommended for phakic intraocular lens patients.
Refractive lens exchange surgery outcomes have been published less in the medical literature. Its frequency of success is believed to be high in appropriate patients, but the risk of retinal detachment may be as high as 8% in selected patients. High myopia without prior posterior vitreous separation can be considered an elevated risk for retinal detachment in refractive lens exchange patients. Postoperative scar formation behind the implant lens is also a possible risk that frequently requires a Nd:YAG laser to eliminate blur.
References
- ↑ Packer M. The implantable collamer lens with a central port: review of the literature. Clin Ophthal 2018;12:2427-2438.
- Huang D, Schallhorn SC, Sugar A, Farjo AA, Majmudar PA, Trattler WB, Tanzer DJ. Ophthalmology. 2009; 116:2244-58. Phakic intraocular lens implantation for the correction of myopia: a report by the American Academy of Ophthalmology.
- Fong CS. Singapore Med J. 2007; 48:709-18. Refractive surgery: the future of perfect vision?
- Koch DD, Harvey TM. Conn's Current Therapy. 2006;227-30. Vision Correction Procedures.
