Changes in Central Corneal Thickness of Preserved Corneas Over Time Measured Using Anterior Segment Optical Coherence Tomography Chul Young Choi,… [605313]

BASICINVESTIGATION
Changes in Central Corneal Thickness of Preserved
Corneas Over Time Measured Using Anterior Segment
Optical Coherence Tomography
Chul Young Choi, MD,* Dong Ju Youm, MD,* Myoung Joon Kim, MD,† and Hungwon Tchah, MD†
Purpose: To measure central corneal thickness (CCT) and
investigate serial changes in CCT, using anterior segment optical
coherence tomography (AS-OCT) on corneas in storage medium.
Methods: Between July and August 2006, 10 human corneoscleral
discs from 5 donors between 19 and 57 years of age were obtained.
Corneoscleral rims were excised and were transferred to Optisol-GS
(Bausch & Lomb, Irvine, CA). After preservation, AS-OCT (Visante
OCT; Carl Zeiss Meditec) was performed on all corneoscleral discs
to detect serial changes in CCT. The corneas were measured with
AS-OCT at 0.5, 1, 2, 3, 4, 6, and 12 hours and then at 1, 2, 3, and
4 days after preservation.
Results: The mean of the baseline CCT measurements obtained
with the ultrasound pachymeter was 632.7 mm. The average CCT on
AS-OCT decreased to 534 mm in the first day of preservation. As
time proceeded, the CCT of each cornea generally decreased. CCT
decreased significantly between 30 minutes and 1 hour after pre-
servation ( P= 0.004). Also, CCT changes in the interval from
preservation to 30 minutes showed a greater decline than during other
intervals. Therefore, the most significant change in CCT occurred in
the first hour after preservation.
Conclusion: AS-OCT offers a fast easy method for evaluating
human donor corneas for corneal thickness and structural changes
without the risk of bacterial contamination or mechanical damage.
Key Words: anterior segment optical coherence tomography, central
corneal thickness, preserved corneas
(Cornea 2009;28:536–540)Penetrating keratoplasty is the most common transplant
operation worldwide. For successful corneal transplanta-
tion, the quality of the donor material is of vital importance.
Standard evaluation of donor corneal material is cur-
rently performed by slit-lamp biomicroscopy of the enucleated
globe. The slit lamp enables accurate observation of the
cornea, revealing early stages of grossly visible pathology.
Besides slit-lamp biomicroscopy of the enucleated eye, several
other methods are available for assessing donor corneal
material; these include light microscopy, ultrasonic methods,
and confocal microscopy. Light microscopy1and slit-lamp
examination have the same requirement for optical transpar-
ency of the donor cornea. Surface screening using ultrasonic
methods2and confocal microscopy3,4cannot be performed
under sterile conditions during storage of potential cornea
transplants.
Clinical measurements of corneal thickness are currently
performed using an optical slit-lamp or ultrasound pachy-
meters. Optical slit-lamp pachymetry is based on a triangula-
tion principle and has a relatively poor precision of 8 mm.5
Ultrasound pachymetry has a precision of approximately
2mm.6However, ultrasound pachymetry requires corneal
contact with a probe or fluid coupling medium, and this creates
difficulty in maintaining sterile conditions.
Optical coherence tomography (OCT) is another
imaging modality that could provide noncontact measurement
of central corneal thickness (CCT).7–10Although previous
investigations were based primarily on a model designed for
posterior segment imaging, anterior segment optical coherence
tomography (AS-OCT) has been introduced recently for
imaging the anterior segment. The AS-OCT systems are based
on low-coherence interferometry using a superluminescent
diode (wavelength of 1310 nm) and are equipped with analysis
software that provides automatic and manual measurements of
CCT. In contrast to ultrasound pachymetry, AS-OCT requires
no contact with the eye.
Neubauer et al11adapted standard retinal OCT for
assessment and follow-up of the corneal disc in organ culture
under sterile conditions and have proven that OCT is an
excellent mode of noncontact examination of corneas in vitro.
OCT has been proposed as a method for donor corneal
screening because of the ability of OCT to make noncontact
measurements through the donor corneal chamber, thereby
preserving tissue sterility. The aim of the present study was to
measure CCT and investigate serial changes in CCT, using
AS-OCT on corneas in storage medium.Received for publication June 4, 2008; revision received September 9, 2008;
accepted October 12, 2008.
From the *Department of Ophthalmology, Sungkyunkwan University School
of Medicine, Kangbuk Samsung Hospital, Seoul, Korea; and †Department
of Ophthalmology, University of Ulsan College of Medicine, Asan
Medical Center, Seoul, Korea.
Supported in part by Grant 2007-049 from the Asan Institute for Life
Sciences, Seoul, Korea.
Presented at the American Society of Cataract and Refractive Surgery
symposium on Cataract, Intraocular Lens and Refractive Surgery, April 27
to May 2, 2007, San Diego, CA.
Reprints: Hungwon Tchah, MD, Department of Ophthalmology, University of
Ulsan College of Medicine, Asan Medical Center, 388-1 Pungnap-2
Dong, Seoul, Korea (e-mail: hwtchah@amc.seoul.kr).
Copyright /C2112009 by Lippincott Williams & Wilkins
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METHODS
Between July 2006 and August 2006, 10 human
corneoscleral discs from 5 donors between 19 and 57 years
of age were obtained from the Eye Bank of the Asan Medical
Center, Seoul, Korea, according to the guidelines of the Eye
Bank Association of America. After obtaining consent from
the donor’ s family, corneal tissue was retrieved by whole globe
enucleation. Whole globes arrived at the eye bank laboratory
and underwent a screening slit-lamp examination.
Corneoscleral rims were excised and were transferred to
Optisol-GS (Bausch & Lomb, Irvine, CA). The mean death-to-
preservation interval of the 10 corneoscleral discs was
187 minutes. Two eyes were preserved in a moist chamber
at 4/C176C within 5 hours after enucleation and then transferred to
Optisol-GS. The other 8 eyes were immediately preserved in
Optisol-GS, after enucleation. Tissue was released to the sur-
geon on the day of surgery after a second screening slit-lamp
examination.
Before preservation, baseline CCT measurements were
obtained for each cornea using an ultrasound pachymeter
(Corneo-Gage Plus; Sonogage, Cleveland, OH). After pres-
ervation, AS-OCT (Visante OCT; Carl Zeiss Meditec) was
performed on all corneoscleral discs, by the same technician,
to detect serial changes in CCT. The corneas were measured
with AS-OCT at 0.5, 1, 2, 3, 4, 6, and 12 hours and then at 1, 2,
3, and 4 days after preservation.
The setup for measurement is shown in Figure 1, with
the corneoscleral disc in a storage bottle held with a custom-
made device. The corneal viewing chamber (Bausch & Lomb)
has a transparent window when viewed from above that allows
the AS-OCT beam to scan the cornea.
The examiner viewed a real-time image of the eye on
a video monitor to allow more precise alignment. The cross-
section was centered on the corneal apex reflection. The
corneal apex was easily identified on real-time OCT images
because the anterior surface reflection was strong. The Visante
OCT methodology allows the cornea to be imaged cross-
sectionally in different meridians. In this study, we used a high-
resolution mode with a horizontal scan line (10 mm with 256
A-scans) particularly selected for CCT measurement. Perpen-
dicularity of the scanning laser beam to the central corneal
surface was adjusted by placing the vertex at the center of the
OCT image and maximizing vertex reflection. The caliper tool
in the Visante OCT software suite was used for manual
measurement (Fig. 2). Three measurements were taken from
each eye, and the average was used in comparisons of CCT.
To analyze serial changes in recorded CCT, independent
sample ttests were performed using SPSS 12.0 (SPSS Inc,
Chicago, IL). A Pvalue of less than 0.05 was considered to be
statistically significant.
RESULTS
The mean age of donors was 32.4 years (range, 19–57
years). The causes of death were trauma (2 donors), sub-
arachnoidal hemorrhage (2 donors), and drug-induced hepatitis
(1 donor). There was no history indicating that any donor had
suffered from ophthalmological disease. On slit-lamp examina-
tion, all corneas appeared normal before and after enucleation.The CCT measurements are presented in Table 1. The
mean of the baseline CCT measurements obtained with the
ultrasound pachymeter was 632.7 mm. The average CCT on
AS-OCT decreased to 534 mm in the first day of preservation.
As time proceeded, the CCT of each cornea generally
decreased, except in the case of the 2 corneas preserved in
a moist chamber. In these corneas, marked swelling occurred
after 5 hours. However, the CCT of these corneas showed
apparent declines after transfer to Optisol-GS. Notably, the
CCT of several corneas decreased to 2 days after preservation.
Figure 3 graphically depicts serial changes in CCT
measurement after preservation. CCT decreased significantly
between 30 minutes and 1 hour after preservation ( P= 0.004).
Also, CCT changes in the interval from preservation to 30
minutes showed a greater decline than during other intervals.
Therefore, the most significant change in CCT occurred in the
first hour after preservation.
DISCUSSION
The measurement of CCT has become increasingly
important in living human eyes. CCT is useful in the diagnosis
of certain corneal diseases and in the monitoring of treatment
FIGURE 1. Setup for AS-OCT measurement of CCT. A storage
bottle containing a corneoscleral disc is placed on a custom-
made holding device while a scan is performed. During this
procedure, the corneoscleral disc remains in its medium,
minimizing the risk of contamination.
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effectiveness. CCT is required for preoperative evaluation
when refractive surgery is considered,12,13for assessment of
corneal endothelial function in contact lens clinics, and for
accurate determination of intraocular pressure to effectively
manage glaucoma patients.14,15
Corneal thickness is known to be associated with the
function and number of corneal endothelial cells in living eyes.
Therefore, although not proved, CCT of donor cornea may
serve as a good reference for the health and number of
endothelial cells during the preservation period and the early
postoperative period when endothelial cell density cannot be
measured.Ultrasound pachymetry is an efficient and accurate
method for measuring corneal thickness and is considered as
the current gold standard. However, it is limited in donor
corneas by being a contact technique with potential draw-
backs of the risk of contamination and epithelial damage
associated with use of an ultrasound probe and introducing
measurement error secondary to probe misplacement or
corneal compression.
The high-speed and noncontact approach offered by AS-
OCT is a promising alternative for assessment of donor
corneas. In living eyes, some studies demonstrated that CCT
measured by AS-OCT was reliable and showed that the data
FIGURE 2. CCT is measured manu-
ally using the caliper tool in the
Visante OCT software suite.
TABLE. 1 CCT Measurements ( mm) on Each Cornea Over Time
Donor BF M* 5H† 1H 2H 3H 4H 6H 12H 1D‡ 2D 3D 4D
1 634 — 590 550 550 540 540 530 530 530 540 540 —
2 630 — 590 540 540 540 540 540 530 530 520 520 —
3 630 — 650 590 590 570 560 560 570 570 550 550 550
4 647 — 620 600 580 600 580 580 580 580 — — —
5 602 — 600 550 530 530 520 520 520 520 — — —
6 626 — 610 560 530 520 520 520 500 500 — — —
7 596 — 590 540 530 530 530 530 520 520 — — —
8 602 — 590 550 540 530 530 530 520 520 — — —
9 677 710 640 600 610 600 580 580 520 530 530 — —
10 683 710 650 630 610 610 590 590 570 540 — — —
Mean 633 — 613 571 561 557 549 548 536 534 — — —
BF, before preservation.
*M, 5 hours in a moist chamber.
†H, hours after preservation.
‡D, days after preservation.
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agreed with those from ultrasound pachymetry.16,17The
advantage of AS-OCT as a noncontact technique is that
preserved corneal discs can be examined while the tissues
remain in sterile medium, thus avoiding the risk of
contamination and epithelial damage.
There have been attempts to use conventional retinal
OCT for donor corneal screening. Neubauer et al11adapted
standard retinal OCT for assessment and follow-up of the
corneal disc in organ culture under sterile conditions and
showed that OCT is an excellent approach for noncontact
examination of corneas in vitro. Earlier studies revealed that
corneal examination by OCT could be appropriate when eye
banks screen donor corneas before laser in situ keratomileusis
surgery.18–20
Over the last 25 years, eye banks have been able to
increase corneal preservation times and improve donor quality.
The evolution of storage media has led to the development of
Optisol, a preservation medium containing dextran, 2.5%
chondroitin sulfate, vitamins, and the precursors of adenosine
triphosphate (adenosine, inosine, and adenine). Optisol
preserves corneal endothelium as effectively as Dexsol
(Chiron Vision, Irvine, CA), the earlier widely used corneal
preservation medium, and is better at preventing stromal
swelling during storage. Corneas stored in Optisol are viable
for 2 weeks if kept refrigerated.21–24Recently, the commer-
cially available corneal preservation medium predominantly
used worldwide is Optisol-GS, which is Optisol (Chiron
Vision) modified by the addition of 200 mg/mL streptomycin
sulfate.
Studies on animal or human corneal thickness changes
upon Optisol storage have been performed. Chang et al25
reported that there was a slight decrease in porcine corneal
thickness during the first 4 hours of preservation, and the
corneas tended to become thicker with increasing preservation
time. The increase was more profound in the second week.
Walkenbach et al24studied rabbit and human corneas stored in
Optisol. Rabbit corneas decreased in thickness within the first
6 hours of storage and then slowly thickened over the next 14
days. Thickness changes in human corneas during storage
were similar to those seen in rabbit tissue, except that the initial
thinning was greater with human corneas.
To the best of our knowledge, the current study
demonstrates, for the first time, serial thickness changes in
the human cornea preserved in Optisol-GS, using AS-OCT.
Here, there was a marked decrease in corneal thickness during
the first hour of preservation, and the corneas tended to
become thinner for up to 2 days after preservation. These
decreases in corneal thickness were presumably caused by the
higher concentration of chondroitin sulfate in Optisol-GS
(compared with the earlier Dexsol solution), which acts to
osmotically remove water from the corneas. It was reported
that Optisol-GS with a concentration of chondroitin sulfate at
2.5% could suppress corneal swelling more effectively than
Dexsol, 1.35%.21–23Whereas the osmolar pressure of aqueous
humor is 303 mOsm/kg26and Dexsol 309 mOsm/kg, the
osmolar pressure of Optisol-GS is 351 mOsm/kg.27The
control of corneal thickness during storage may serve as
a good reference for corneal function after storage, and such
control has also significant clinical implications. Manysurgeons prefer a relatively thin cornea at the time of
keratoplasty because such corneas are more transparent than
thicker corneas and offer better handling characteristics and
easier apposition to the host cornea.
This study had several limitations. Although a single
investigator performed all CCT measurements, we cannot
exclude the possibility that the inspector became more
accurate with increasing experience. It is difficult to perform
AS-OCT on a preserved cornea in a storage bottle. However,
the more the examiner performed this task, the more skillful he
became. As donation of cornea is limited in Korea, the donor
corneas of this study are of small number. The availability of
more preserved corneas, stored for longer preservation times,
might have allowed us to more accurately measure serial
changes in the CCT of preserved corneas.
CCT measurements with AS-OCT may put to practical
use in some fields because evaluations of imported donor
corneas and precut tissue in Descemet stripping automated
endothelial keratoplasty and studies on donated corneal tissue
and corneal storage medium. With imported donor corneas,
each cornea is screened and stored according to a standard eye
bank procedure before being shipped for transportation. The
long transportation period, the inevitable vibration, and
unexpected shifts in temperature might damage the delicate
donor corneal endothelium.28,29Even though reevaluation of
corneas after transportation is difficult, CCT measurements
using AS-OCT may be suitable to evaluate the condition of
imported donor corneas. Recent studies reported that the use
of precut tissue for Descemet stripping automated endothelial
keratoplasty is not associated with increased risk of
complications related to tissue preparation.30–32However,
many surgeons still concern about the possibility of adverse
tissue changes that may occur between the now extended time
when the tissue is precut and the time it is transplanted.33–35
CCT measurements with AS-OCT may be an easy method and
FIGURE 3. Serial changes in CCT after preservation.
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good reference for the health of endothelial cells during the
preservation. Besides, serial CCTwith AS-OCT may be useful
in performing study on donated corneal tissue and corneal
storage medium.
In conclusion, AS-OCT offers a fast easy method for
evaluating human donor corneas for corneal thickness and
structural changes without the risk of bacterial contamination
or mechanical damage.
REFERENCES
1. Borderie V , Martinache C, Sabolic V , et al. Light microscopic evaluation
of human donor corneal stroma during organ culture. Acta Ophthalmol
Scand . 1998;76:154–157.
2. Pavlin CJ, Sherar MD, Foster FS. Subsurface ultrasound microscopic
imaging of the intact eye. Ophthalmology . 1990;97:244–250.
3. Lemp MA, Dilly PN, Boyde A. Tandem-scanning (confocal) microscopy
of the full-thickness cornea. Cornea . 1985–1986;4:205–209.
4. Patel S, McLaren J, Hodge D, et al. Normal human keratocyte density and
corneal thickness measurement by using confocal microscopy in vivo.
Invest Ophthalmol Vis Sci . 2001;42:333–339.
5. Ehlers N, Hansen FK. On the optical measurement of corneal thickness.
Acta Ophthalmol (Copenh) . 1971;49:65–81.
6. Reinstein DZ, Silverman RH, Trokel SL, et al. Corneal pachymetric
topography. Ophthalmology . 1994;101:432–438.
7. Muscat S, McKay N, Parks S, et al. Repeatability and reproducibility of
corneal thickness measurements by optical coherence tomography. Invest
Ophthalmol Vis Sci . 2002;43:1791–1795.
8. Sin S, Simpson TL. The repeatability of corneal and corneal epithelial
thickness measurements using optical coherence tomography. Optom Vis
Sci. 2006;83:360–365.
9. Bechmann M, Thiel MJ, Neubauer AS, et al. Central corneal thickness
measurement with a retinal optical coherence tomography device versus
standard ultrasonic pachymetry. Cornea . 2001;20:50–54.
10. Wong AC, Wong CC, Yuen NS, et al. Correlational study of central
corneal thickness measurements on Hong Kong Chinese using optical
coherence tomography, Orbscan and ultrasound pachymetry. Eye. 2002;
16:715–721.
11. Neubauer AS, Priglinger SG, Thiel MJ, et al. Sterile structural imaging
of donor cornea by optical coherence tomography. Cornea . 2002;21:
490–494.
12. Emara B, Probst LE, Tingey DP , et al. Correlation of intraocular pressure
and central corneal thickness in normal myopic eyes and after laser in situ
keratomileusis. J Cataract Refract Surg . 1998;24:1320–1325.
13. Price FW Jr, Koller DL, Price MO. Central corneal pachymetry in patients
undergoing laser in situ keratomileusis. Ophthalmology . 1999;106:2216–
2220.
14. Whitacre MM, Stein RA, Hassanein K. The effect of corneal thickness on
applanation tonometry. Am J Ophthalmol . 1993;115:592–596.
15. Herndon LW , Choudhri SA, Cox T, et al. Central corneal thickness in
normal, glaucomatous, and ocular hypertensive eyes. Arch Ophthalmol .
1997;115:1137–1141.
16. Li H, Leung CK, Wong L, et al. Comparative study of central corneal
thickness measurement with slit-lamp optical coherence tomographyand visante optical coherence tomography. Ophthalmology . 2008;115:
796–801.
17. Li EY, Mohamed S, Leung CK, et al. Agreement among 3 methods to
measure corneal thickness: ultrasound pachymetry, Orbscan II, and
Visante anterior segment optical coherence tomography. Ophthalmology .
2007;114:1842–1847.
18. Priglinger SG, Neubauer AS, May CA, et al. Optical coherence
tomography for the detection of laser in situ keratomileusis in donor
corneas. Cornea . 2003;22:46–50.
19. Wolf AH, Neubauer AS, Priglinger SG, et al. Detection of laser in situ
keratomileusis in a postmortem eye using optical coherence tomography.
J Cataract Refract Surg . 2004;30:491–495.
20. 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.
21. Kaufman HE, Beuerman RW , Steinemann TL, et al. Optisol corneal
storage medium. Arch Ophthalmol . 1991;109:864–868.
22. Lindstrom RL, Kaufman HE, Skelnik DL, et al. Optisol corneal storage
medium. Am J Ophthalmol . 1992;114:345–356.
23. Lass JH, Bourne WM, Musch DC, et al. A randomized, prospective,
double-masked clinical trial of Optisol vs DexSol corneal storage media.
Arch Ophthalmol . 1992;110:1404–1408.
24. Walkenbach RJ, Boney F, Y e GS. Corneal function after storage in dexsol
or optisol. Invest Ophthalmol Vis Sci . 1992;33:2454–2458.
25. Chang SW , Wang YH, Pang JH. The effects of epithelial viability on
stromal keratocyte apoptosis in porcine corneas stored in Optisol-GS.
Cornea . 2006;25:78–84.
26. Caprioli J. The ciliary epithelia and aqueous humor. In: Hart WM Jr, ed.
Adler’s Physiology of the Eye . 9th ed. St. Louis, MO: CV Mosby;
1992:228.
27. Tachibana A, Sawa M. Development of novel corneal storage medium:
first report. Examinations of rabbit cornea. Jpn J Ophthalmol . 2002;46:
377–383.
28. Wang IJ, Hu FR. Effect of shaking of corneal endothelial preservation.
Curr Eye Res . 1997;16:1111–1118.
29. Anderson SA, Story PG. Freezing of preservation media during corneal
tissue transport. J Ophthalmic Nurs Technol . 1996;15:19–20.
30. Kitzmann AS, Goins KM, Reed C, et al. Eye bank survey of surgeons
using precut donor tissue for descemet stripping automated endothelial
keratoplasty. Cornea . 2008;27:634–639.
31. Price MO, Baig KM, Brubaker JW , et al. Randomized, prospective
comparison of precut vs surgeon-dissected grafts for descemet stripping
automated endothelial keratoplasty. Am J Ophthalmol . 2008;146:36–41.
32. Chen ES, Terry MA, Shamie N, et al. Precut tissue in Descemet’ s stripping
automated endothelial keratoplasty donor characteristics and early
postoperative complications. Ophthalmology . 2008;115:497–502.
33. Suwan-Apichon O, Reyes JM, Griffin NB, et al. Microkeratome
preparation of lamellar corneal grafts. Eye Contact Lens . 2006;32:
248–249.
34. Suwan-Apichon O, Reyes JM, Griffin NB, et al. Microkeratome versus
femtosecond laser predissection of corneal grafts for anterior and posterior
lamellar keratoplasty. Cornea . 2006;25:966–968.
35. Rose L, Bricen ˜o CA, Stark WJ, et al. Assessment of eye bank-prepared
posterior lamellar corneal tissue for endothelial keratoplasty. Ophthal-
mology . 2008;115:279–286.
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