Comparison of Central Corneal Thickness and Peripheral Corneal Thickness using Sheimpflug system, Optical Coherence Tomography and Ultrasound Pachymetry in Normal, Keratoconus and Post-Refractive Surgery Eyes at Different Corneal Thickness.

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Comparison of Central Corneal Thickness and
Peripheral Corneal Thickness using Sheimpflug
system, Optical Coherence Tomography and
Ultrasound Pachymetry in Normal, Keratoconus and
Post-Refractive Surgery Eyes at Different Corneal
Thickness.
Ricardo N. Sepulveda, MD Claudia Maria Prospero
Ponce, MS Karolinne Maia Rocha, MD PhD William J.
Dupps, MD PhD Ronald R. Krueger, MD Cole Eye
Institute Cleveland, OH Authors have no
financial interest.
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Background
Purpose To compare central corneal thickness
(CCT) and peripheral corneal thickness (PCT) with
scheimpflug system (Pentacam), high-speed optical
coherence tomography (Visante) and ultrasound
pachymetry (US) in normal eyes, keratoconus
suspect and post-laser in situ keratomileusis
(LASIK). Setting Department of Refractive
Surgery, Cole Eye Institute, The Cleveland
Clinic. Cleveland, Ohio, USA. Study Type
Retrospective Analysis
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Introduction

• Ultrasound pachymetry is currently the gold
  standard in measuring CCT.
• Measurements taken with Pentacam and Visante-OCT
  have demonstrated to be comparable to US.
• To our knowledge, this is the first study
  comparing central pachymetry between the 3
  systems in pre- and post-LASIK eyes, and
  keratoconus suspects.

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Patients and Methods

• The CCT and PCT were measured with Pentacam
  (Oculus Inc, Lynnwood, WA, USA) , US (Sonogage,
  Corneo-Gage Plus, Sonogage Inc., USA) and
  Visante OCT(Carl Zeiss Meditec Inc., Dublin, CA,
  USA,) in 163 eyes of 83 patients.
• 3 groups were retrospectively analyzed
  Keratoconus suspects, Post-LASIK and Normal
  patients (without Corneal pathology).
• Keratoconus suspects were identified by the
  Rabinowitz-Macdonald criteria and using the
  PathFinder II Corneal Analysis Software for the
  ATLAS Corneal Topography System (Model 9000).
• Influence of age and corneal thickness was
  evaluated in all groups, categorizing eyes with
  thin (500µm), normal (501-550µm) or thick
  (551µm) corneas using US values.

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Patients and Methods

• Data was collected at 0 mm and 6 mm from
  Pentacam, 0-2mm and 5-7mm from OCT, and a single
  value was obtained from US.
• Multivariate generalized estimating equations
  were used to analyze the correlations between the
  3 measurements obtained from the patients both
  eyes.
• Mean CCT and mean PCT difference between devices
  were obtained for each group using multivariate
  linear regression.
• Analyzed factors included age, keratoconus
  suspects and previous refractive surgery (LASIK)
  subsequently, influence of absolute corneal
  thickness in pachymetry measurements was
  determined.

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Results

• 83 patients (163 eyes)
• Mean age 39 years (range 22-69 yrs.)
• 53 female, 30 male
• 40 eyes were keratoconus suspects, 17 post LASIK
  and 103 normal eyes.
• Mean spherical equivalent (SE) and Keratometry
  (Km) are shown in Table 1.
• Keratometry readings ranged from 36.2 D to 59.5
  D.
• Mean CCT for each group is shown in Table 2.

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Results

• CCT measurements were higher in US compared with
  Pentacam (6.49 1.84µ plt0.0005) and Visante OCT
  (7.481.38µ plt0.0005) for keratoconus suspects,
  post LASIK and normal eyes, regardless of age and
  corneal thickness.
• The greatest difference in mean CCT measurements
  was observed in the post-LASIK group (Table 3),
  where Pentacam measured thinner CCT than US and
  OCT.
• Peripheral corneal thickness measurements were
  superior in Pentacam than in OCT(603.26 38.83µ
  vs. 570.6140.39µ plt0.0005).

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Results
All All Normal Keratoconus Post Lasik
SE -3.78 3.36 -4.17 3.03 -4.09 3.75 -0.78 2.29
Km 44.77 2.14 44.63 1.31 46.04 2.6 42.2 2.4
Table 1. Spherical equivalent and Km for all the
eyes and for each individual group
Mean Normal Keratoconus Post LASIK
CCT (value SD) US Pentacam OCT 52328.04 516.2831.6 515.4129.16 523.0241.61 513.5743.96 512.6742.31 526.0666.73 501.6673.74 516.3566.14
PCT (value SD) Pentacam OCT 597.3734.20 564.2634.8 575.0545.28 608.9742.79 628.8246.91 60049.79
Table 2. Mean central(CCT) and peripheral(PCT)
corneal thickness with standard deviation in the
3 groups.
Mean Difference US vs. Pentacam P value US vs OCT P value Pentacam vs OCT P value
CCT (value SD) Constant Keratoconus Post LASIK 6.491.84 4.07 3.34 17.754.86 0.0005 0.224 0.0005 7.481.38 3.282.51 2.04 3.63 0.0005 0.190 0.575 0.891.39 0.212.58 15.613.66 0.521 0.935 0.0005
Table 3. Mean central corneal thickness
difference between Ultrasound, Pentacam and
Visante OCT pachymetries in a paired analysis.
Standard deviation is also shown. P value lt0.05
was statistically significant
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Results
Mean Difference Pentacam vs OCT P value
PCT (value SD) Constant Keratoconus Post LASIK 1.25.05 4.497.14 33.162.71 0.0005 0.812 0.53
Table 4. Peripheral corneal thickness was higher
in Pentacam than in Visante OCT (constant). No
influence was observed in Keratoconus or Post
LASIK patients. P value was statistically
significant if lt0.05
Mean Difference US vs Pentacam P value US vs OCT P Value Pentacam vs OCT P Value
CCT (value SD) Thick Thin Constant 6.263.67 1.933.22 7.662.07 0.089 0.550 0.0005 3.62.64 -2.132.32 8.231.47 0.173 0.359 0.0005 -2.083.02 -4.442.67 0.681.64 0.491 0.096 0.679
Table 5. US gives thicker measurements than OCT
and Pentacam(plt0.0005). The difference between US
and Pentacam were similar at any absolute corneal
thickness. gt551µm 500µm
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Results
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Results
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Conclusion

• These recently new devices do not replace US
  pachymetry  but rather complement each other in
  the preoperative evaluation of refractive surgery
  candidates, aid in the diagnosis and treatment of
  keratoconus suspects, help evaluate the lens,
  screen for glaucoma and allow room for more
  research in all ophthalmologic fields.
• Ophthalmologists should be familiar with the
  difference in CCT between US, Pentacam and
  Visante OCT.
• Pentacam and Visante OCT can be used
  interchangeably for central pachymetry, however,
  in post LASIK patients, Visante OCT might perform
  better pachymetry maps than Pentacam.
• Further studies are suggested in order to
  establish the influence of age in peripheral
  pachymetry.