Clinical significance of central corneal thickness and comparison of central corneal thickness measurements methods

Abstract

Significance of central corneal thickness has been increasing in ophthalmology practice. It is an important clinical evaluation tool especially prior to refractive surgery and in diagnosis of glaucoma and keratoconus. Refractive surgery is planned according to preoperative central corneal thickness measurements. Besides, in order to determine actual intraocular pressure, central corneal thickness is measured and corrected eye pressure is obtained. Today, devices used in measurement of central corneal thickness do the measurement according to two principles. First and relatively older method is ultrasonic method. Optic method is the second and more recent method. In daily practice, the most commonly used clinical method in measurement of central corneal thickness is ultrasound pachymeter. However, this measurement technique requires contact between cornea and probe and gives thinner measurement results compared to the methods that use optic principle. Recently, several technologic methods based on optics have been put in use; they provide advantages of non-contact technique and objective determination of central corneal thickness. Of these methods, most commonly used include Specular Microscopy, Optical coherence tomography, Laser Doppler Interferometry, Optical low coherence reflectometry pachymetry, Optic based topographic mapping (also called screening section pachymetry) and Pentacam. In this article, it was aimed to evaluate importance of central corneal thickness in clinical use and compare measurement methods. J Clin Exp Invest 2014; 5 (1): 153-158

Keywords

• Central corneal thickness, glaucoma, refractive surgery, ultrasound pachymetry, optical method

Santral kornea kalınlığının klinik önemi ve santral kornea kalınlığı ölçüm yöntemlerinin karşılaştırılması

Öz

Santral kornea kalınlığının önemi oftalmoloji pratiğinde zaman geçtikçe artmaktadır. Bilhassa refraktif cerrahi öncesinde, glokom ve keratokonus tanısının konulması gibi klinik durumlarda önemli bir klinik değerlendirme aracıdır. Özellikle, refraktif cerrahi rutin olarak operasyon öncesi santral kornea kalınlığı ölçümüne göre planlanmaktadır. Ayrıca intraoküler basıncın doğru tespit edilebilmesi için de santral kornea kalınlığı ölçülüp düzeltilmiş göz tansiyonu belirlenir. Günümüzde santral kornea kalınlığı ölçümünde kullanılan aletler iki prensibe göre ölçüm yapmaktadır. Birinci ve nisbeten daha eski bir yöntem olan ultrasonik yöntem, ikinci ve daha yeni bir yöntem olan optik yöntemdir. Pratikde SKK ölçülmesinde en sık kullanılan klinik yöntem ultrason pakimetresidir. Ancak bu ölçüm yöntemi, kornea-prob teması gerektirmektedir ve kornea yüzeyindeki mekanik basınçtan dolayı optik prensip ile ölçüm yapan yöntemlere göre daha ince ölçüm değerleri vermektedir. Son yıllarda, non-kontakt teknik ve santral kornea kalınlığının objektif belirlenmesi avantajlarını sunan optik temele dayanan birçok teknolojik yöntemler kullanılmaya başlanmıştır. Bu yöntemlerin günümüzde en çok kullanılanları ise speküler mikroskobi, optik koherens tomografi, lazer doppler interferometri, optik düşük koherens reflektometri pakimetresi, optik temelli topografik haritalama sistemi ya da diğer adıyla tarayıcı kesit pakimetre ve pentacam olarak sıralanabilir. Bu makalede santral kornea kalınlığının klinik kullanımda öneminin anlaşılması ve ölçüm yöntemlerinin bilinmesi amaçlanmıştır.

Anahtar Kelimeler

• Santral kornea kalınlığı, glokom, refraktif cerrahi, ultrason pakimetri, optik yöntem

References

1. 1. Pflugfelder SC, Liu Z, Feuer W, et al. Corneal thickness indices discriminate between keratoconus and contact lens-induced corneal thinning. Ophthalmology 2002;109:2336-2341.
2. 2. Holden BA, Mertz GW, McNally JJ. Corneal swelling response to contact lenses worn under extended wear conditions. Invest Ophthalmol Vis Sci.1983;24:218- 226.
3. 3. Academy of Ophthalmology. Excimer laser photorefractivekeratectomy (PRK) for myopia and astigmatism. Ophthalmic procedure preliminary assessment. Ophthalmology 1999;106:422-437.
4. 4. Price FW Jr, Koller DL, Price MO. Central corneal pachymetry in patients undergoing laser in situ keratomileusis. Ophthalmology 1999;106:2216-2220.
5. 5. Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol 2000;44:367-408.
6. 6. Gordon MO, Beiser JA, Brandt JD, et al. The Ocular Hypertension Treatment Study; baseline factors that predict the onset of primary openangl glaucoma; the Ocular Hypertension Treatment Study Group. Arch Ophthalmol 2002;120:714-720.
7. 7. Doughman D. The Cornea. In: Principles and Practise of Ophthalmology. Peyman GA,Sanders DR, Goldberg MF (Eds). WB. Saunders Company, Philadelphia, 1989;356-339.
8. 8. Martola EL, Baum JL. Central and peripheral corneal thickness: A clinical study. Arch Ophthalmol1968;79:28.

9. 9. Waring OG. Corneal Structure and Pathophysiology. In: Corneal Disorders Clinical Diagnosis and Management. Leibowitz HM (Ed). W. B. Saunders Company, Philadelphia.1984;1-265.
10. 10. Harris JE, Nordqist Lt. The hydration of the cornea. Am J Ophthalmol1955;40:100.
11. 11. Mishima S, Hedbys BO. The permeability of the corneal epithelium and endothelium. Exp Eye Res1967;6:10.
12. 12. Klyce SO, Beurman RW. Structure and function of cornea. In: The Cornea. Kaufman HE, Baron BA, McDonald MB, Waltman SR (Eds). Churchill Livingstone New York, 1998;3-54.
13. 13. Dohlman CH, Hedbys BO, Mishima S. The swelling pressure of the corneal stroma, Invest Ophthalmol Vis Sci 1962;1:158.
14. 14. Mauric DM. The permeability to sodium ions of the living rabbit’s cornea. J Physiol 1951;112:367.
15. 15. Ytteborg J, Dohlman CH. Corneal edema and intraocular pressure: ii. Clinical results. Arch Ophthalmol 1965;74:477.
16. 16. Fogagnolo P, Rossetti L, Mazzolani F, Orzalesi N. Circadian variations in central corneal thickness and intraocular pressure in patients with glaucoma. Br J Ophthalmol 2006;90:24-28.
17. 17. Korey M, Gieser D, Kass MA. Central corneal endothelial density and central corneal thickness in ocular hypertension and primary open angle glaucoma. Am J Ophthalmol 1982;94:610-616.
18. 18. Gagnon MM. Corneal endotelial cell density in glaucoma. Cornea 1997;16:318.
19. 19. Blix M.Oftalmometriska studier. Uppsala Lakareförenings Förhandlingar 1879;15:349-420.
20. 20. Maurice DM, Giardini AA. A simple optical apparatus for measuring the corneal thickness and the average thickness of the human cornea. Br J Ophthalmol 1951:35:169-177.
21. 21. Olsen T, Ehlers N. The thickness of the human cornea as determined by a specular method. Acta Ophthalmol. 1984;62:859-871.
22. 22. Jaeger W. Tiefemnmessung der menschlichen Vonderkammer mit planparallelen Platten. 1982;52:850-854.
23. 23. Hansen FK. A clinical study of the normal human central corneal thickness. Acta Ophthalmol 1971;49:82- 89.
24. 24. Green DG, Frueh BR, Shapiro JM. Corneal thickness measured by interferometry. J Opt Soc Am 1975;65:119-123.
25. 25. Suzuki S, Oshika T, Oki K, et al. Corneal thickness measurements: scanning-slit corneal topography and noncontact specular microscopy versus ultrasonic pachymetry J Cataract Refr Surg 2003;29:1313-1318.
26. 26. Kremer FB, Walton P, Gensheimer G. Determination of corneal thickness using ultrasonic pachymetry. Ann OphthalmoI 1985;17:506-507.
27. 27. Sarışın E, Kevser Ma, Eren H, Kaya V. Ultrasonik Pakimetre İle Kornea Kalınlıklarının Ölçümü. T Oft Gaz 1992;22:441.
28. 28. Edmund C. Determination of the corneal thickness profile by optical pacometry. Acta Ophthalmol. 1987;65:147.
29. 29. Doughty M, Zaman M. Human corneal thickness measures: a review and meta-analysis approach. Surv Ophthalmol 2000;44:367-408.
30. 30. McLaren JW, Nau CB, Erie JC, Bourne WM. Corneal thickness measurement by confocal microscopy,ultrasound, and scanning slit methods. Am J Ophthalmol 2004;137:1011-1020.
31. 31. Kawana K, Tokunaga T, Miyata K, et al. Comparison of corneal thickness measurements using Orbscan II, non-contact specular microscopy, and ultrasonic pachymetry in eyes after laser in situ keratomileusis. Br J Ophthalmol 2004;88:466-468.
32. 32. Bovelle R, Kaufmann SC, Thompso SW. Corneal thickness measurements with the Topcon SP-2000P specular microscope and an ultrasound pachymeter. Arch Ophthalmol 1999;117:868-870.
33. 33. Nissen J, Hjordal JO, Ehlers N. A clinical comparison of optical and ultrasonic pachymetry. Acta Ophthalmol 1991;69:659-663.
34. 34. Miglior S, Albe E, Guareschi M, et al.: Intraobserver and interobserver reproducibility in the evaluation of ultrasonic pachymetry measurements of central corneal thickness. Br J Ophthalmol 2004;88:174-177.
35. 35. Wheeler NC, Morantes CM, Kristensen RM. Reliability coefficients of three corneal pachymeters. Am J Ophthalmol 1992;113:645- 651.
36. 36. Yeniad B, Cakici O, İzgi B. Evaluation of corneal thickness with pentacam and ultrasonic pachymetry and assessment of the effect of corneal thickness on intraocular pressure. Glokom-Katarakt 2010;2:093-096
37. 37. Buyuk K, Bozkurt B, Kamis Ü, et al. Comparison of central corneal thickness measurements in normal and keratoconic eyes using ultrasonic pachymetry and OCULUS Pentacam. Turk J Ophtalmol 2011;3:104- 107
38. 38. Yazici AT, Pekel G, Bozkurt E, et al. Measurements of anterior segment parameters using three different non-contact optical devices in keratoconus patients. Int J Ophthalmol 2013;6:521-525.