Historically, obtaining accurate measurement of corneal pachymetry was not a critical part of tissue evaluations performed by the eye bank. Simply noting the presence and perceived severity of stromal edema with increased corneal thickness would be reported as part of slit-lamp evaluation of a cornea. However, as endothelial keratoplasty began to become more common around 2006, accurate corneal pachymetry of donor tissue became increasingly important (Fig. 1).1
In the mid-2000s, when donor preparation for Descemet stripping automated endothelial keratoplasty (DSAEK) began being performed in the eye bank setting, the ability to accurately measure corneal thickness became critical.2–4 Early adopters relied on handheld pachymeter units to obtain accurate readings of corneal thickness at the time of tissue processing. Although these handheld units provided eye banks with accurate pachymetry, they were not without issue.
Because pachymetry was performed at the same time as DSAEK preparation, an eye bank may not know that a cornea is too thick or too thin to process until the cornea had already been removed from its storage solution and mounted on an artificial anterior chamber. The use of the handheld unit during processing also extended the time a cornea spent out of storage solution and required the processing eye bank to touch a nonsterile probe to the cornea to obtain readings.
The ability to obtain accurate thickness measurement before DSAEK processing became increasingly important as surgeon preferences for final DSAEK graft thicknesses became more specific.5 Specular microscopes have the ability to measure corneal thickness through obtaining an in-focus image of the endothelium and an in-focus image of the epithelium and measuring the distance the stage travels between those images. This provided the advantage of knowing the corneal thickness before processing; however, because of the subjectivity of technicians, it was difficult to measure only epithelial thickness and often times still required the use of a handheld pachymeter unit during processing.
With the increasing need to know corneal thickness with a high degree of accuracy (including being able to precisely measure the thickness of the corneal epithelium), eye banks began using optical coherence tomography (OCT) in the late 2000s.6 The first adopters of this technology immediately saw tremendous benefit in obtaining OCT images before processing tissue and further benefit in integrating the use of OCT in routine evaluation of donor tissue (Fig. 2).
The most widely adopted OCT model used by contributors of images for this Atlas was the Optovue RTVue (Fremont, CA) (Fig. 3). Other OCT models included the Envisu R Series SDOCT (Leica Microsystems Inc, Buffalo Grove, IL) and the Carl Zeiss Visante (Dublin, CA). All of these models give eye bank personnel the ability to accurately analyze donor corneas to determine their suitability for various surgical uses.
Beyond accurate measurement of corneal thickness (Fig. 4), OCT imagery allows for highly accurate measurements of anterior scars to determine whether a cornea can be processed for use in DSAEK preparation.7 OCT imagery also allows eye bank personnel to accurately measure the stroma and epithelium separately. Armed with this knowledge, eye bank personnel can develop a detailed plan before processing such as determining the appropriate microkeratome head size or whether to remove the epithelium before processing. With a plan in place, eye banks are able to provide DSAEK grafts within the requested thickness parameters. OCT can also be used to identify potential stromal infiltrates, distinguished from simple epithelial exposure. And finally, OCT may aid eye banks in screening for refractive surgery.8
OCT imagery has become an important addition to the eye banking community's tool kit to continue to ensure that appropriate donor corneas are being provided for surgical use. This atlas will illustrate its usage in various eye banking situations and how it complements other donor cornea evaluation technologies.
2. Brown JS, Wang D, Li X, et al. In situ ultrahigh-resolution optical coherence tomography characterization of eye bank corneal tissue processed for lamellar keratoplasty. Cornea. 2008;27:802–810.
3. Tang M, Stoeger C, Galloway J, et al. Evaluating DSAEK graft deturgescence in preservation medium after microkeratome cut with optical coherence tomography. Cornea. 2013;32:847–850.
4. Woodward MA, Titus MS, Shtein RM. Effect of microkeratome pass on tissue processing for Descemet stripping automated endothelial keratoplasty. Cornea. 2014;33:507–509.
5. Neff KD, Biber JM, Holland EJ. Comparison of central corneal graft thickness to visual acuity outcomes in endothelial keratoplasty. Cornea. 2011;30:388–391.
6. Eye Bank Association of America. Medical Standards. Washington, DC: Eye Bank Association of America; 2017.
7. Bald MR, Stoeger C, Galloway J, et al. Use of Fourier-domain optical coherence tomography to evaluate anterior stromal opacities in donor corneas. J Ophthalmol. 2013;2013:397680.
8. Lin RC, Li Y, Tang M, et al. Screening for previous refractive surgery in eye bank corneas by using optical coherence tomography. Cornea. 2007;26:594–599.