Journal of Refractive Surgery

Report 

Moderate Keratoconus With Thick Corneas

Thaís Bacha Berti, MD; Vinícius Coral Ghanem, MD, PhD; Ramon Coral Ghanem, MD, PhD; Perry S. Binder, MS, MD

Abstract

PURPOSE:

To describe two patients with moderate keratoconus and a corneal thickness exceeding 600 μm at the thinnest point.

METHODS:

Case report.

RESULTS:

In the first case, the steepest keratometric power was 51.50 diopters (D) in the right eye and 53.4 in the left eye and the thickness at the thinnest point was 658 and 625 μm, respectively. In the second case, the steepest keratometric power was 46.70 D in the right eye and 49.60 D in the left eye and the thickness at the thinnest point was 618 and 608 μm, respectively.

CONCLUSIONS:

Keratoconus may develop despite a very thick cornea, reinforcing the idea that biomechanical changes can signify an important factor in the development and progression of this pathology.

[J Refract Surg. 2013;29(6):430–435.]

From Sadalla Amin Ghanem Eye Hospital, Joinville, SC, Brazil (TBB, VCG, RCG); and Gavin Herbert Eye Institute, University of California, Irvine, California (PSB).

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (TBB, RCG, VCG); data collection (TBB, VCG); analysis and interpretation of data (PSB, TBB, RCG, VCG); drafting of the manuscript (PSB, TBB, VCG); critical revision of the manuscript (TBB, RCG, VCG); administrative, technical, or material support (PSB, VCG); supervision (VCG)

Correspondence to: Vinícius Coral Ghanem, MD, PhD, Sadalla Amin Ghanem Eye Hospital, Rua Abdon Batista 172, Joinville, SC 89201-010, Brazil. E-mail: vcghanem@hotmail.com

Received: May 01, 2012
Accepted: February 26, 2013

Abstract

PURPOSE:

To describe two patients with moderate keratoconus and a corneal thickness exceeding 600 μm at the thinnest point.

METHODS:

Case report.

RESULTS:

In the first case, the steepest keratometric power was 51.50 diopters (D) in the right eye and 53.4 in the left eye and the thickness at the thinnest point was 658 and 625 μm, respectively. In the second case, the steepest keratometric power was 46.70 D in the right eye and 49.60 D in the left eye and the thickness at the thinnest point was 618 and 608 μm, respectively.

CONCLUSIONS:

Keratoconus may develop despite a very thick cornea, reinforcing the idea that biomechanical changes can signify an important factor in the development and progression of this pathology.

[J Refract Surg. 2013;29(6):430–435.]

From Sadalla Amin Ghanem Eye Hospital, Joinville, SC, Brazil (TBB, VCG, RCG); and Gavin Herbert Eye Institute, University of California, Irvine, California (PSB).

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (TBB, RCG, VCG); data collection (TBB, VCG); analysis and interpretation of data (PSB, TBB, RCG, VCG); drafting of the manuscript (PSB, TBB, VCG); critical revision of the manuscript (TBB, RCG, VCG); administrative, technical, or material support (PSB, VCG); supervision (VCG)

Correspondence to: Vinícius Coral Ghanem, MD, PhD, Sadalla Amin Ghanem Eye Hospital, Rua Abdon Batista 172, Joinville, SC 89201-010, Brazil. E-mail: vcghanem@hotmail.com

Received: May 01, 2012
Accepted: February 26, 2013

Keratoconus is a non-inflammatory corneal ectasia characterized by progressive thinning of the central and paracentral portion of the cornea, resulting in variably decreased vision, depending on the severity of the disease.1,2

In addition to topography, corneal thickness (ultrasound or tomography) is an important clinical parameter altered by this pathology.2–4 An abnormally thin cornea is also considered a risk factor for eyes undergoing LASIK or photorefractive keratectomy surgery.5 Previous reviews of corneal thickness in cases of keratoconus have reported an ultrasonic mean central thickness of 485 ± 29 μm,1 494.2 ± 50 μm,2 523 ± 41 μm,3 and 462.5 ± 8 μm.6 According to Gherghel et al.,3 the mean corneal thickness at the thinnest point in patients with keratoconus evaluated by corneal tomography was 424 ± 70 μm and the maximum corneal thickness at the thinnest point documented in the researched literature was 602 μm.

We present two unusual patients with keratoconus who had a corneal thickness greater than 600 μm at the thinnest point.

Case Reports

Case 1

A 37-year-old woman was examined in April 2007. She was previously clinically diagnosed as having keratoconus, but without prior topography. She had never worn contact lenses. She complained of visual difficulty in both eyes and bilateral ocular itching. She had been using the same glasses for 5 years (−0.75 −2.50 × 29 in the right eye and −1.25 – 3.75 × 164 in the left eye). Her previous medical history consisted of active polycystic ovary syndrome. There was no family history of keratoconus, corneal transplants, sporadic eye rubbing, and no known atopic diseases in the patient or her family.

The best corrected visual acuity was 20/25 in the right eye and 20/25− in the left eye with her current spectacles. The manifest refraction was −1.50 −1.50 × 30 (20/20−) in the right eye and −0.50 – 3.00 × 170 (20/25−) in the left eye. Intraocular pressure by applanation was 16 mm Hg in both eyes. The biomicroscopic examination showed a clear cornea with a steep central curvature. Corneal topography in the right eye (Medmont, Vermont, Australia) revealed keratoconus with a paracentral, inferior steepening with a maximum keratometric power of 51.50 D and a paracentral inferior steepening in the right eye and a maximum keratometric power of 53.40 D in the left eye (Figures 1A and 1B ). The thickness at the thinnest point evaluated by Orbscan II (Bausch & Lomb, Rochester, NY) was 658 μm in the right eye and 625 μm in the left eye using a correction factor of 8% (Figures 1C and 1D ). The central cornea thickness measured by ultrasonic pachymetry was 672 μm in the right eye and 667 μm in the left eye. Specular microscopy (SP-2000P; Topcon, Tokyo, Japan) showed 3,329 cells/mm2 in the right eye and 3,834 cells/mm2 in the left eye. We referred her to the Contact Lens Department to improve her visual acuity.

Case 1. Topography showed inferior and nasal keratoconus in the right eye, with a maximum keratometric power in the apex of (A) 51.50 diopters in the right eye and (B) 53.40 diopters in the left eye. Orbscan II (Bausch & Lomb, Rochester, NY) showed a thinnest point of (C) 658 μm in the right eye and (D) 625 μm in the left eye. GALILEI Analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland) showed corneal thickness at the thinnest point of (E) 624 μm in the right eye and (F) 610 μm in the left eye.

Figure 1. Case 1. Topography showed inferior and nasal keratoconus in the right eye, with a maximum keratometric power in the apex of (A) 51.50 diopters in the right eye and (B) 53.40 diopters in the left eye. Orbscan II (Bausch & Lomb, Rochester, NY) showed a thinnest point of (C) 658 μm in the right eye and (D) 625 μm in the left eye. GALILEI Analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland) showed corneal thickness at the thinnest point of (E) 624 μm in the right eye and (F) 610 μm in the left eye.

On September 15, 2011, the manifest refraction had slightly worsened in the right eye to −1.75 −2.00 × 15 (20/25) but appeared stable in the left eye at −1.00 − 2.75 × 165 (20/25). We repeated the tomography examinations using the GALILEI Analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland), which showed the corneal thickness in the thinnest point to be 624 μm in the right eye and 610 μm in the left eye (Figures 1E and 1F ). Specular microscopy was 2,696 cells/mm2 in the right eye and 2,806 cells/mm2 in the left eye. The central corneal thickness on ultrasound pachymetry was 648 μm in the right eye and 622 μm in the left eye.

Case 2

A 38-year-old man was examined in April 2001. He had been previously diagnosed as having keratoconus. He complained of a gradual worsening of vision in both eyes over several years, which did not improve with glasses. He had a habit of rubbing his eyes. There was nothing of note in his previous medical history. There was no family history of keratoconus.

The best corrected visual acuity was 20/30 in the right eye and 20/30− in the left eye. The manifest refraction was plano −0.75 × 75° (20/25) in the right eye and +0.75 −1.25 × 85° (20/30) in the left eye. The biomicroscopy showed slight conjunctival discoloration with a mild mucoid discharge in both eyes and a clear cornea. Corneal topography (Medmont) showed an inferior, peripheral keratoconus in the right eye with an apical maximum keratometric power of 46.70 D in the right eye and 49.60 D in the left eye (Figures 2A and 2B ). The corneal thickness at the thinnest point evaluated by Orbscan II (Bausch & Lomb) was 618 μm in the right eye and 608 μm in the left eye using a correction factor of 8% (Figures 2C and 2D ). Specular microscopy (EM-3000; Tomey, Nagoya, Japan) was 2,625 cells/mm2 in the right eye and 2,526 cells/mm2 in the left eye. We recommended a contact lens fitting to improve his visual acuity.

Case 2. Topography (Medmont, Vermont, Australia) shows an inferior keratoconus with a maximum keratometric power of (C) 46.70 diopters in the right eye and (D) 49.60 diopters in the left eye. Orbscan II (Bausch & Lomb, Rochester, NY) showing a thinnest point of (C) 618 μm in the right eye and (D) 608 μm in the left eye.

Figure 2. Case 2. Topography (Medmont, Vermont, Australia) shows an inferior keratoconus with a maximum keratometric power of (C) 46.70 diopters in the right eye and (D) 49.60 diopters in the left eye. Orbscan II (Bausch & Lomb, Rochester, NY) showing a thinnest point of (C) 618 μm in the right eye and (D) 608 μm in the left eye.

Discussion

We report two cases of patients with moderate keratoconus with a corneal thickness at the thinnest point of greater than 605 μm by tomography. One of the eyes with a maximum keratometric power of 51.50 D had a thickness at the thinnest point of 648 μm. The classification used was based on the steepest keratometric power (moderate 46 to 52 D).7 To our knowledge, the maximum central corneal thickness reported in patients with keratoconus using the Orbscan II and ultrasonic pachymetry was 576 and 627 μm, respectively3 (Table 1 ). These values are lower than those found in this report. Ultrasound pachymetry was also used to confirm the measurements from Orbscan in the central cornea and we used a second tomography device (GALILEI Analyzer) more than 3 years after the initial consultation to confirm the measurements in case 1 (Figures 1C and 1D ). Another uncommon feature was the mirror symmetry observed on the GALILEI Analyzer and Orbscan topography. It is difficult to explain the reason for this finding, but it may be that this feature is more frequent in patients with keratoconus who have thick corneas.

Reported Maximum CCT and TCT in the Thinnest Point in Patients With Keratoconus

Table 1: Reported Maximum CCT and TCT in the Thinnest Point in Patients With Keratoconus

The differences between the thinnest point and the central cornea were 26 μm in the right eye and 48 μm in the left eye in case 1 and 9 μm in the right eye and 12 μm in the left eye in case 2. The differences observed in case 2 were lower than those observed in case 1 due to more advanced keratoconus. The difference between the mean apical corneal thickness and the mean central corneal thickness measured by Orbscan was 36.9 μm in Haque et al.2 and 34.4 μm in Gherghel et al.3 The keratoconus apex location and the severity of the disease are the two main reasons that this difference can vary significantly.

There was no correlation between the thinnest point and posterior elevation (an unusual finding for a patient with keratoconus) in case 2. This lack of correlation may be due to the atypical corneal thickness and the peripheral keratoconus location. The corneal asymmetry observed in the topography was much higher than the 1.4 to 1.6 for the normal cornea. The low power on the horizontal axis was probably due to the peripheral location of the process. There was no sign of pellucid marginal degeneration in the topography, nor was there any peripheral thinning.

Uçakhan et al.6 evaluated mean central corneal thickness in patients with keratoconus and subdivided them into three groups based on the mean keratometric power (light > 47 D, moderate 47 to 55 D, and severe > 55D). The mean central corneal thickness in patients with moderate keratoconus was 433 ± 15 μm using the Pentacam and 444 ± 11 μm using ultrasonic pachymetry (Table 2 ). Considering these values, a central corneal thickness greater than 600 μm in our patients with moderate keratoconus was more than 10 standard deviations from the mean. A comparison of the reported corneal thickness in the thinnest point of eyes with keratoconus and in our study is presented in Table 1 .

Mean CCT Evaluation in Patients With Keratoconus Using Different Methods

Table 2: Mean CCT Evaluation in Patients With Keratoconus Using Different Methods

It has been suggested that corneal thickness is an important risk factor in the development of ectasia after refractive surgery.5 However, ectasia has occurred in some patients without any of the proposed risk factors.8 Our report shows that unknown factors that affect the individual cornea’s biomechanical stability could be responsible for some of the reported cases of ectasia in corneas with a normal thickness, and that keratoconus may develop and evolve despite a thick cornea, reinforcing the idea that biomechanical changes to the cornea can signify an important factor in the development and progression of this pathology. A thick cornea does not mean a biomechanically stronger cornea.9–12 These characteristics are linked to individual constitutional factors such as the stromal biochemical composition, including types of collagen found in the cornea and the quantity of glycosaminoglycans, among other still relatively unknown factors.11,12

We wish to stress that the specular microscopy results of our patients were normal, presenting no evidence whatsoever of endothelial disease. The endothelial mosaic had normal appearance at all examinations. The difference of almost 20% between examinations in case 1 was probably because the measurements were performed using two different devices. The first result of 3,329 cells/mm2 in the right eye and 3,834 cells/mm2 in the left eye are above that expected for the patients’ age. The second measurement of 2,696 cells/mm2 in the right eye and 2,806 cells/mm2 in the left eye also did not show any signs of endothelial disease.

References

  1. Kawana K, Miyata K, Tokunaga T, et al. Central corneal thickness measurements using Orbscan II scanning slit topography, noncontact specular microscopy, and ultrasonic pachymetry in eyes with keratoconus. Cornea. 2005;24:967–971 doi:10.1097/01.ico.0000159733.37554.ba [CrossRef] .
  2. Haque S, Simpson T, Jones L. Corneal and epithelial thickness in keratoconus: a comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography. J Refract Surg. 2006;22:486–493.
  3. Gherghel D, Hosking SL, Mantry S, et al. Corneal pachymetry in normal and keratoconic eyes: Orbscan II versus ultrasound. J Cataract Refract Surg. 2004;30:1272–1277 doi:10.1016/j.jcrs.2003.11.049 [CrossRef] .
  4. Luz A, Ursulio M, Castanheda D, Ambrosio R Jr, . Corneal thickness progression from the thinnest point to the limbus: study based on a normal and a keratoconus population to create reference values [article in Portuguese]. Arq Bras Oftalmol. 2006;69:579–583 doi:10.1590/S0004-27492006000400023 [CrossRef] .
  5. Randleman JB, Woodward M, Lynn MJ, Stulting RD. Risk assessment for ectasia after corneal refractive surgery. Ophthalmology. 2008;115:37–50 doi:10.1016/j.ophtha.2007.03.073 [CrossRef] .
  6. Uçakhan OO, Ozkan M, Kanpolat A. Corneal thickness measurements in normal and Keratoconic eyes: Pentacam comprehensive eye scanner versus noncontact specular microscopy and ultrasound pachymetry. J Cataract and Refractive Surgery. 2006;30:970–977 doi:10.1016/j.jcrs.2006.02.037 [CrossRef] .
  7. Zadnik K, Barr JT, Edrington TB, et al. Baseline findings in the collaborative longitudinal evaluation of keratoconus (CLEK) study. Invest Ophthalmol Vis Sci. 1998;39:2537–2546.
  8. Tuli SS, Iyer S. Delayed ectasia following LASIK with no risk factors: is a 300-micron stromal bed enough?J Refract Surg. 2007;23:620–622.
  9. Ortiz D, Pinero D, Shabayek M, et al. Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes. J Cataract Refract Surg. 2007;33:1371–1375 doi:10.1016/j.jcrs.2007.04.021 [CrossRef] .
  10. Toubout D, Roberts C, Kérautret J, et al. Correlations between corneal hysteresis, intraocular pressure and corneal central pachymetry. J Cataract Refract Surg. 2008;34:616–622 doi:10.1016/j.jcrs.2007.11.051 [CrossRef] .
  11. Kotecha A, Elsheikh A, Roberts CR, Zhu H, Garway-Heath DF. Corneal thickness and age-related biomechanical properties of the cornea measured with the ocular response analyzer. Invest Ophthalmol Vis Sci. 2006;47:5337–5347 doi:10.1167/iovs.06-0557 [CrossRef] .
  12. Luce DA. Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J Cataract Refract Surg. 2005;31:156–162 doi:10.1016/j.jcrs.2004.10.044 [CrossRef] .
  13. Shah S, Laiquzzaman M, Bhojwani R, Mantry S, Cunliffe I. Assessment of the biomechanical properties of the cornea with the ocular response analyzer in normal and keratoconic eyes. Invest Ophthalmol Vis Sci. 2007;48:3026–3031 doi:10.1167/iovs.04-0694 [CrossRef] .
  14. Gromacki SJ, Barr JT. Central and peripheral corneal thickness in keratoconus and normal patient groups. Optom Vis Sci. 1994;71:437–441 doi:10.1097/00006324-199407000-00003 [CrossRef] .
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  16. Prospero Ponce CM, Rocha KM, Smith SD, Krueger RR. Central and peripheral corneal thickness measured with optical coherence tomography, Scheimpflug imaging, and ultrasound pachymetry in normal, keratoconus-suspect, and post-laser in situ keratomileusis eyes. J Cataract Refract Surg. 2009;35:1055–1062 doi:10.1016/j.jcrs.2009.01.022 [CrossRef] .

Reported Maximum CCT and TCT in the Thinnest Point in Patients With Keratoconus

Study Orbscan II ( μ m)
Ultrasonic Pachymetry ( μ m)
Specular Microscopy ( μ m)
UBM ( μ m)
CCT TCT CCT TCT CCT TCT
Current (4 eyes) Case 1-OD/OS: 684/673; Case 2-OD/OS: 627/620 Case 1-OD/OS: 658/625; Case 2-OD/OS: 618/608 Case 1-OD/OS: 672/667; Case 2-OD/OS: NA NA Case 1-OD/OS: 648/622; Case 2-OD/OS: 594/595 NA
Kawana et al. 1 (22 eyes) 530 NA 548 NA 529 NA
Ghergel et al. 3 (64 eyes) 576 602a 627 620a NA NA
Shah et al. 13 (93 eyes) NA NA 611 NA NA NA
Luz et al. 4 NA 540a NA NA NA NA
Avitabile et al. 15 (30 eyes) NA NA NA NA NA 420a

Mean CCT Evaluation in Patients With Keratoconus Using Different Methods

Study Pentacam ( μ m) Ultrasonic Pachymetry ( μ m) Specular Microscopy ( μ m) Orbscan II ( μ m) OCT ( μ m)
Uçkhan et al. 6 (62 eyes) Mild KC: 478.6 ± 10.5; Moderate KC = 433.7 ± 14.7; Severe KC: 358.2 ± 19.2 Mild KC: 481.9 ± 10.3; Moderate KC: 444.2 ± 11.4; Severe KC: 385.2 ± 14.7 Mild KC: 464.8 ± 10.2; Moderate KC: 426.9 ± 11.4; Severe KC: NA NA NA
Kawana et al. 1 (22 eyes) NA 485.0 ± 29.3 (422–548) 476.7 ± 28.3 (404–529) 449.5 ± 43.5 (346–530) NA
Haque et al. 2 (40 eyes) NA 494.2 ± 50.0 (NA) NA 438.6 ± 47.7 (NA) 433.5 ± 39.7 (NA)
Prospero Ponce et al. 16 (40 eyes) 514 ± 44.0 (NA) 523 ± 41.6 (NA) NA NA 512.7 ± 42.3 (NA)
Ghergel et al. 3 (64 eyes) NA 502.8 ± 52.5 (392–627) NA 458.8 ± 62.5 (322–576) NA
Gromacki & Barr 14 (28 eyes) NA 520 ± 40 (370–600) NA NA NA

10.3928/1081597X-20130515-05

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