The Influence of Age on the Refractive Index of the Human Corneal Stroma Resected Using a Mechanical Microkeratome

Purpose: To measure the refractive index (RI) of the human corneal stroma in vivo using an objective Abbé refractometer (VCH-1) and to determine if RI of the stroma is related to age. Methods: The VCH-1 was calibrated against a standard subjective Abbé refractometer using 7 randomly selected turbid semiliquid media. VCH-1 was used to measure RI at the central midstroma immediately after lifting the flap in neophyte patients preselected for laser-assisted in situ keratomileusis. Surgical procedures continued as preplanned after measuring the RI; in binocular cases, measurements were taken from the right eye only. Flaps were created using a mechanical microkeratome. Results: The VCH-1 was capable of measuring the RIs of all 7 turbid semiliquid media. The average RMS difference between RI estimates according to the VCH-1 and standard subjective Abbé refractometer was 0.003. The mean RI (±SD) of the stroma was 1.369 (±0.008; range, 1.356–1.390), and the mean age (±SD) of the subjects was 33.7 years (±8.86; range, 18–56 years). A significant linear correlation was found between age and RI. Least squares regression lines equating RI with age (x, years) was of the form: RI = 1.35711 + 0.00034x (r = +0.383, n = 36, P = 0.011). Conclusions: RI of the stroma in vivo has a tendency to be increased in older patients when the stroma is resected using a mechanical microkeratome.

[1]  J. Alió,et al.  Changes in the refractive index of the human corneal stroma during laser in situ keratomileusis: Effects of exposure time and method used to create the flap , 2008, Journal of cataract and refractive surgery.

[2]  S. Mishima,et al.  Flow of water in the corneal stroma. , 1962, Experimental eye research.

[3]  J. Alió,et al.  Refractive index change in bovine and human corneal stroma before and after lasik: a study of untreated and re-treated corneas implicating stromal hydration. , 2004, Investigative ophthalmology & visual science.

[4]  F. Fitzke,et al.  Refractive index of the human corneal epithelium and stroma. , 1995, Journal of refractive surgery.

[5]  M. C. Leske,et al.  Corneal thickness and intraocular pressure in the Barbados eye studies. , 2003, Archives of ophthalmology.

[6]  I. Fatt,et al.  Flow conductivity of human corneal stroma. , 1970, Experimental eye research.

[7]  D. Maurice.  The structure and transparency of the cornea , 1957, The Journal of physiology.

[8]  J. Alió,et al.  Human Cornea Before and After Refractive Surgery Using a New Device: VCH-1 , 2008, Cornea.

[9]  M. O'Neal,et al.  Decreased endothelial pump function with aging. , 1986, Investigative ophthalmology & visual science.

[10]  J. Ytteborg,et al.  Corneal edema and intraocular pressure. II. Clinical results. , 1965, Archives of ophthalmology.

[11]  D. Altman,et al.  STATISTICAL METHODS FOR ASSESSING AGREEMENT BETWEEN TWO METHODS OF CLINICAL MEASUREMENT , 1986, The Lancet.

[12]  M. Kass,et al.  Central corneal endothelial cell density and central corneal thickness in ocular hypertension and primary open-angle glaucoma. , 1982, American journal of ophthalmology.

[13]  R A Laing,et al.  Changes in the corneal endothelium as a function of age. , 1976, Experimental eye research.

[14]  A. Gezer.  The Role of Patient's Age in Regression of Holmium: Yag Thermokeratoplasty-Induced Correction of Hyperopia , 1997, European journal of ophthalmology.

[15]  T. Olsen,et al.  THE THICKNESS OF THE HUMAN CORNEA AS DETERMINED BY A SPECULAR METHOD , 1984, Acta ophthalmologica.

[16]  A. Beckett,et al.  AKUFO AND IBARAPA. , 1965, Lancet.

[17]  Liu Pengcheng,et al.  Central corneal thickness in adult Chinese , 2008, Journal of Huazhong University of Science and Technology [Medical Sciences].

[18]  S. Azen,et al.  Central corneal thickness in Latinos. , 2003, Investigative ophthalmology & visual science.

[19]  M. Yamauchi,et al.  Cross-linking and the molecular packing of corneal collagen. , 1996, Biochemical and biophysical research communications.

[20]  R. Flom,et al.  Age differences in corneal hydration control. , 1989, Investigative ophthalmology & visual science.

[21]  C. R. Worthington,et al.  The structure of cornea , 1984, Quarterly Reviews of Biophysics.

[22]  D J Coleman,et al.  The shape of Bowman's layer in the human cornea. , 1998, Journal of refractive surgery.

[23]  H. Nomura,et al.  The relationship between age and intraocular pressure in a Japanese population: The influence of central corneal thickness , 2002, Current eye research.

[24]  K. Meek,et al.  Changes in the refractive index of the stroma and its extrafibrillar matrix when the cornea swells. , 2003, Biophysical journal.

[25]  R. S. Wall,et al.  Ageing of the human corneal stroma: structural and biochemical changes. , 1992, Biochimica et biophysica acta.

[26]  Srinivas K. Rao,et al.  Corneal Endothelial Cell Density and Morphology in Normal Indian Eyes , 2000, Cornea.

[27]  A. Daxer,et al.  Collagen fibrils in the human corneal stroma: structure and aging. , 1998, Investigative ophthalmology & visual science.

[28]  A. Robert,et al.  Corneal collagens. , 2001, Pathologie et biologie.

[29]  W. D. Wright.  Physiological Optics , 1958, Nature.

[30]  T. Olsen,et al.  Light scattering from the human cornea. , 1982, Investigative ophthalmology & visual science.

[31]  C. McGhee,et al.  Age-related differences in the normal human cornea: a laser scanning in vivo confocal microscopy study , 2007, British Journal of Ophthalmology.

[32]  D Hodge,et al.  Normal human keratocyte density and corneal thickness measurement by using confocal microscopy in vivo. , 2001, Investigative ophthalmology & visual science.

[33]  S. Patel,et al.  Refractive index of the mammalian cornea and its influence during pachometry. , 1987, Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians.

[34]  Shan C. Lin,et al.  Central corneal thickness of Caucasians, Chinese, Hispanics, Filipinos, African Americans, and Japanese in a glaucoma clinic. , 2004, Ophthalmology.

[35]  A. Elsheikh,et al.  Assessment of Corneal Biomechanical Properties and Their Variation with Age , 2007, Current eye research.

[36]  J. McLaren,et al.  Variations in human corneal endothelial cell morphology and permeability to fluorescein with age. , 1988, Experimental eye research.

[37]  R. Guthoff,et al.  Depth and age‐dependent distribution of keratocytes in healthy human corneas: A study using scanning‐slit confocal microscopy in vivo , 2002, Journal of cataract and refractive surgery.

[38]  G. Kaye.  Stereologic measurement of cell volume fraction of rabbit corneal stroma. , 1969, Archives of ophthalmology.

[39]  Luis Alonso,et al.  The relationship between central corneal thickness and Goldmann applanation tonometry , 2003, Clinical & experimental optometry.

[40]  H. Edelhauser,et al.  In vitro corneal endothelial permeability in rabbit and human: the effects of age, cataract surgery and diabetes. , 1989, Experimental eye research.