Morphometric study was conducted on 28, serially sectioned staged human embryos. The cornea is of equal thickness during its early development (stages 15&plusmn;17). During developmental stages 18 and 19 (7 th week) it is thicker in the central part. In the last embryonic week the peripheral part of the cornea becomes thicker than its central part. The performed study elucidates structural differentiation during development of the cornea

Bruska, Małgorzata

Styszyński, Andrzej

Woźniak, Witold

English

Via Medica Journals

Folia Morphol. Vol. 60, No. 1, pp. 5759Copyright ' 2001 Via MedicaISSN 00155659www.fm.viamedica.plO R I G I N A L  A R T I C L E57Address for correspondence: Witold Woniak, PhD, Department of Anatomy, University School of Medical Sciences, ul. wiŒcickiego 6,60781 Poznaæ, Poland, tel: +61 869 91 81, fax: +61 865 89 85, e-mail: wwozniak@usoms.poznan.plMorphometric study of the corneain human embryosAndrzej Styszyæski, Ma‡gorzata Bruska, Witold WoniakDepartment of Anatomy, Karol Marcinkowski University School of Medical Sciences, Poznaæ, Poland[Received 2 January  2001; Accepted 15 January 2001]Morphometric study was  conducted on 28, serially sectioned staged humanembryos. The cornea is of equal thickness during its early development (stages1517). During developmental stages 18 and 19 (7th week) it is thicker in thecentral part. In the last embryonic week the peripheral part of the cornea be-comes thicker than its central part. The performed study elucidates structuraldifferentiation during development of the cornea.key words: human eye, development, embryonic period, cornea,morphometryINTRODUCTIONMost of the interest in the development of the humancornea has been concentrated on the early differenti-ation and structure of that eye coat [13,5,10,1517].Morphometric studies on the eyes of human embry-os and fetuses have been very few, frequently at var-ious periods of development, and no line of conti-nuity could be established to allow the growth ofthe organ as a whole to be followed. ORahilly andBossy [9] established the growth curve of the hu-man embryonic and fetal eyeballs, basing on linearmeasurements and the volume of the eyes. Staflova[11] related the size of the eye to the age of humanembryos and fetuses, showing that the developmentof the eye is very stable as compared to other or-gans.Harayama et al. [4] measured the diameters ofthe cornea and eyeball in 220 human fetuses agedfrom 12 to 28 weeks.In our previous morphometric studies [12,13] thehuman embryonic retina and lens were investigated.In the present study we measured the thicknessof the cornea in 28 human embryos aged from 36to 56 days and correlated our data with histologicalfindings.MATERIAL AND METHODSThe study was  conducted on 28 staged humanembryos from the collection of the Department ofAnatomy, University School of Medical Sciences inPoznaæ. All embryos were embedded in toto in para-plast and sectioned serially. The age of the embryoswas estimated according to the criteria of the Carn-egie Embryological Institute and expressed in pos-tovulatory days and in developmental stages. Serialsections, 5 µm thick, were stained with hematoxylinand eosine. Morphometric studies included the thick-ness of the cornea in its centre and at its periphery.Measurements were made, with a Leica Image Pro-cessing and Analysis System, for 5 consecutive sec-tions and for each section the cornea was measuredin 10 different axes. Thus in each embryo 50 mea-surements were made from which the main valuewas calculated (Table 1).RESULTSThe cornea appears in human embryos at stage 15.In these embryos the restored surface ectodermforms the anterior epithelium of the cornea, whichhas its own basement membrane. By stage 19 mes-enchyme grows between the surface ectoderm and58Folia Morphol., 2001, Vol. 60, No. 1Table 1. Thickness of cornea in relation to embryonic ageStage C-R Length Age Thickness of corneain mm in days in mmCentre Periphery15 8.0 36 0.008 – 0.001 0.009 – 0.00115 8.0 36 0.011 – 0.001 0.010 – 0.00115 8.5 36 0.010 – 0.001 0.009 – 0.00115 9.0 36 0.010 – 0.001 0.008 – 0.00116 10.0 38 0.011 – 0.001 0.010 – 0.00116 10.0 38 0.010 – 0.001 0.011 – 0.00116 10.0 38 0.012 – 0.001 0.009 – 0.00116 11.0 38 0.009 – 0.001 0.012 – 0.00116 11.0 38 0.010 – 0.001 0.012 – 0.00116 12.0 38 0.009 – 0.001 0.010 – 0.00117 12.0 41 0.009 – 0.001 0.008 – 0.00117 13.0 41 0.010 – 0.001 0.010 – 0.00117 13.0 41 0.011 – 0.001 0.009 – 0.00117 14.0 41 0.013 – 0.001 0.011 – 0.00118 15.0 44 0.012 – 0.001 0.009 – 0.00118 16.0 44 0.011 –0.001 0.010–0.00119 17.0 46 0.024 – 0.002 0.021 – 0.00219 18.0 46 0.023 – 0.002 0.022 – 0.00220 20.0 49 0.019 – 0.002 0.024 – 0.00220 20.0 49 0.018 – 0.002 0.023 – 0.00220 21.0 49 0.020 – 0.002 0.026 – 0.00321 22.0 51 0.022 – 0.002 0.035 – 0.00321 23.0 51 0.021 – 0.002 0.034 – 0.00322 25.0 53 0.033 – 0.003 0.047 – 0.00422 26.0 53 0.028 – 0.003 0.045 – 0.00423 30.0 56 0.081 – 0.007 0.093 – 0.00823 30.0 56 0.074 – 0.006 0.088 – 0.00723 31.0 56 0.079 – 0.006 0.085 – 0.007lens epithelium, forming substantia propria, whichbecomes thicker on periphery to the end of the em-bryonic period.Results of the performed study (Table 1) showthat the thickness of the cornea in its centre and atthe periphery is almost equal by stage 17 (41 posto-vulatory days). The cornea becomes thicker in thecentre in embryos of developmental stages 18 and19 (44 and 46 postovulatory days). During the 8thweek of the embryonic period (stages 2023, 5156postovulatory days) the cornea becomes thicker atits periphery as compared to its central portion.DISCUSSIONThe cornea is formed from the surface ectoderm,mesenchyme, and neural crest cells. From the sur-face ectoderm is derived the external corneal epi-thelium. The mesenchyme gives rise to the substan-tia propria, and the neural crest cells migrate fromthe lip of the optic cup through the embryonic con-nective tissue and differentiate into the corneal epi-thelium. Formation of the cornea is induced by thelens vesicle [14]. This induction results in the trans-formation of a typical surface ectoderm into a trans-parent, multilayered structure with a complex extra-cellular matrix and cellular contribution from sever-al sources.In human embryos at stage 15 the early corneaconsists of the anterior epithelium, which is trans-formed basal ectodermal cells [68]. In developmen-tal stages 16 and 17 the cornea consists of the ante-rior epithelium, mesostroma and mesothelium [1,15]. Our study showed that at these stages the thick-ness of the cornea is equal throughout its wholesurface.During stage 18 and 19 the mesenchyme, consti-tuting the future substantia propria of the cornea,invades the interval between the surface ectodermand the lens epithelium, and the posterior epitheliumof the cornea becomes clearly distinguishable [69].This developmental event is expressed in greaterthickness of the centre of the cornea, which is evi-dent in our morphometric study.In the last week of the embryonic period (stages2023) the substantia propria of the cornea increas-es in thickness and is formed by 5 to 6 layers. It be-comes thicker on periphery. This was confirmed inthe present investigations.It has to be pointed out that differences in thick-ness between the centre and periphery of the adultcornea are already marked in the last embryonicweek.REFERENCES1. Ewer MS (1979) Zur Frühentwiclung des Stroma cor-neae und der Pupillarmembran beim Menschen. ActaAnat, 75: 3746.2. Fischer F (1928) Zur Entwiclungsgeschichte der Horn-haut des Menschen. Z Augenhlk, 64: 293310.3. Hagedoorn A (1928) The early development of the endot-helium of Descements membrane, the cornea and theanterior chamber of the eye. Br J Ophtalmol, 12: 479495.4. Harayama K, Amemiya T, Nishimura H (1980) Devel-opment of the cornea during fetal life: comparison ofcorneal and bulbar diameter. Anat Rec, 198: 531535.5. Israel NE (1929) Contribution to the development ofthe human cornea. Am J Ophtalmol, 12: 469475.59Andrzej Styszyæski et al., Thickness of human embryonic cornea6. ORahilly R (1966) The early development of the eye instaged human embryos. Contr Embryol Carneg Instn,38: 142.7. ORahilly R (1975) The prenatal development of thehuman eye. Exp Eye Res, 21: 93112.8. ORahilly R (1983) The timing and sequence of events inthe development of the human eye and ear during theembryonic period proper. Anat Embryol, 168: 8799.9. ORahilly R, Bossy J (1972) The growth of the eye. Part1: in utero. Annal Desarollo, 16: 3151.10. Scammon RE, Armstrong EL (1925) On the growth ofthe human eyeball and optic nerve. J Comp Neurol,38: 165219.11. Stalova J (1971) Relation of the size of the eye to theage and length in human ontogenesis. Am J ObstetGynecol, 110: 126128.12. Styszyæski A, Woniak W, Bruska M (1997) Morpho-metric study of the lens in staged human embryos.Folia Morphol, 56: 267272.13. Styszyæski A, Woniak W, Bruska M (1998) Morpho-metric study of the human embryonic retina. FoliaMorphol, 57: 212220.14. Tripathi BJ, Tripathi RC, Livingstone AM, Borisuth NSC(1991) The role of growth factors in the embryogene-sis and differentiation of the eye. Am J Anat, 192: 442471.15. Wulle KG (1972) Electron microscopy of the fetal de-velopment of the corneal endothelium and Desce-ments membrane of the human eye. Invest Ophthal-mol, 11: 897904.16. Wulle KG, Lerche W (1969) Electron microscopic ob-servations of the early development of the human cor-neal endothelium and Descements membrane. Oph-thalmologica, 157: 451461.17. Wulle KG, Richter J (1978) Electron microscopy of theearly embryonic development of the human cornealepithelium. Graefes Arch Clin Exp Ophthalmol, 209:3949.60Folia Morphol., 2001, Vol. 60, No. 1

Morphometric study of the cornea in human embryos

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Morphometric study of the cornea in human embryos

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