Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue (the graft).
When the entire cornea is replaced it is known as penetrating keratoplasty and when only part of the cornea is replaced it is known as lamellar keratoplasty. Keratoplasty simply means surgery to the cornea.
The graft is taken from a recently deceased individual with no known diseases or other factors that may affect the chance of survival of the donated tissue or the health of the recipient.
The cornea is the transparent front part of the eye that covers the iris, pupil and anterior chamber. The surgical procedure is performed by ophthalmologists, physicians who specialize in eyes, and is often done on an outpatient basis.
Corneal transplantation is performed when medicines, keratoconus conservative surgery and cross-linking can no longer heal the cornea.
This surgical procedure usually treats corneal blindness, with success rates of at least 41% as of 2021.
Corneal diseases are a leading cause of blindness with an estimated 10 million patients diagnosed with bilateral corneal blindness worldwide.
Corneal transplantation is highly successful in low-risk patients with corneal blindness but often fails those with high-risk indications such as recurrent or chronic inflammatory disorders, history of glaucoma and herpetic infections, and those with neovascularisation of the host bed.
Moreover, the need for donor corneas greatly exceeds the supply, especially in disadvantaged countries.
The outermost layer, the epithelium, which makes up 10% of the total corneal thickness, consists of stratified cells with tight junctions, that form a protective barrier. Between the epithelium and stroma is the Bowman's layer, an acellular layer often known as a modified extension of stroma.
The stroma makes up 90% of the total corneal thickness. It protects the eye from the external environment while contributing to 65–75% of all light transmission to the retina, enabling vision.
Separating the posterior corneal stroma and endothelium is the Descemet's membrane, which is a dense, thick, somewhat transparent, cell-free matrix. For those with corneal melting disorders, the Descemet's membrane is sometimes the only layer remaining to keep the eye's integrity.
The endothelium is made up of a single layer of hexagonal cells. The function of the endothelium is to regulate and maintain stromal hydration. Collectively, the cornea is a highly complex tissue, innervated and avascular.
Most patients starting their search for refractive surgery initially consider LASIK, PRK, or SMILE. That said, corneal pathology, such as epithelial basement membrane dystrophy, Fuchs’ endothelial dystrophy, keratoconus, pterygiums, RK scars and Salzmann’s nodules, can eliminate these patients as ideal candidates for some procedures.
The good news: The implantation of lenses (or “lens refractive surgery”) is a group of procedures that patients who have concurrent corneal disease can often benefit from.
In our practice, we find that phakic IOLs, including the Visian Implantable Collamer Lens (ICL) (Staar Surgical) and the Visian Toric Implantable Collamer Lens (TICL) (Staar Surgical) are options to consider for young myopes who have corneal disease.
Phakic IOLs bypass an otherwise compromised cornea in a way that does not cause the corneal disease to worsen.
Typically, we implant ICLs in myopic, or nearsighted, patients who are between 21 to 45 years of age and have more than -3.00 D, but less than -15.00 D of sphere, as ICLs are FDA approved for these refractive errors.
We implant TICLs in patients who have myopic astigmatism and 1.0 D to 4.0 D of cylinder at the spectacle plane.
We have successfully treated patients who are highly myopic, have a large amount of astigmatism and keratoconus, or other causes of stromal thinning and protrusion, who need options other than glasses, contact lenses, or laser vision correction to help them see their best.
Something else to consider: Due to reduced image minification, correction of refraction near the nodal point of the eye, it is not rare to observe patients gaining lines of best-corrected visual acuity (BCVA).
In fact, in a subset of a report of our first-year experience using the TICL post-FDA approval, we looked at 31 eyes that were not correctable to 20/20 preoperatively, most due to corneal abnormalities, and found a statistically significant improvement in BCVA of one line of visual acuity on average.
Furthermore, many of these eyes had postoperative Uncorrected VA that exceeded preoperative BCVA.
Based on these results and other published reports of ICLs in the setting of corneal disease, we believe ICLs are safe and effective at correcting myopia with and without astigmatism when corneal disease, such as keratoconus and corneal scars, are present.
Oftentimes, we see patients seeking a second opinion because they’ve been told they aren’t candidates for LASIK, but still have the desire to reduce their need for contact lenses and glasses.
The majority of the patients we see are thrilled when informed that lens refractive surgery may be suitable for them.
We believe our role is to inform the patient of every option possible to provide the best visual outcome, while taking into account whether corneal disease (or other ocular disease, for that matter) is present.
To ensure a satisfactory surgical outcome for these patients, we take multiple corneal topography images to check for abnormalities on the anterior surface of the eye.
If there are abnormalities, such as Salzmann’s nodules or pterygia, we typically recommend removing those surface irregularities first; then bringing the patient back for a series of repeat scans and topographies before discussing with the patient which IOL we feel will best fit their needs.
In the case of Salzmann’s nodules or pterygia, we have experienced that corneal topography images before and after removal can decrease the amount of astigmatism drastically, affecting not only the power of toric IOL needed, but also the spherical power of the lens.
Furthermore, some of these patients have a desire to have not only their distance vision corrected, but also their near. However, not all patients adapt well to monovision; and we typically do not recommend multifocal or trifocal IOLs to patients if they have significant corneal disease.
We’ve implanted the Crystalens AO (Bausch + Lomb) IOL and the Trulign Toric IOL (Bausch + Lomb), which provide excellent optics, particularly for distance and intermediate vision, but may still require reading glasses.
Most patients entering our offices seek surgical solutions for not only pathology, like corneal disease and cataract, but also a wide range of refractive errors they may present with.
As corneal physicians, we are fortunate to have the technologies and surgical techniques to match a wide variety of patient needs and desires.
We believe it is our job to diagnose and treat pathology, and also to help meet the desires of our patients as they relate to dependence on external optical aids, such as contact lenses and glasses.
Utilizing lens refractive surgery, we have many options to mask corneal abnormalities to help our patients and provide good, quality vision.