Corneal endothelial cell abnormalities in X-linked Alport syndrome.

Background: X-linked Alport syndrome results from the effect of COL4A5 mutations on basement membranes in the kidney, ear and eye. This study investigated individuals with X-linked Alport syndrome for corneal abnormalities.Patients and Methods: Six men and four women from 8 families with genetically-diagnosed X-linked Alport syndrome underwent ophthalmological examination including slit lamp examination and corneal endothelial specular microscopy. Results for corneal microscopy for men and women with X-linked disease were compared separately with the mean values for age- matched normals using the student's t test.Results: Five of the 6 men had end-stage kidney failure, all 6 had a hearing loss, three had lenticonus, and three had a central fleck retinopathy. Two men had a history of recurrent corneal erosions but no evidence of posterior polymorphous corneal dystrophy. None of the four women had kidney failure, but two had a hearing loss, and two had a central fleck retinopathy. One woman, whose son had recurrent corneal erosions, also had erosions, but no features of a posterior polymorphous corneal dystrophy.Corneal specular microscopy demonstrated abnormalities in affected men and women, with larger endothelial cells (p = .0001 in men, p = .004 in women) fewer 6-sided cells (p = .0001, p = .001 respectively) and reduced cell density (p = .03, p = .02 respectively) than normal.Conclusions: Recurrent corneal erosions are common in men and women with X-linked Alport syndrome, but posterior polymorphous corneal dystrophy is rare. The abnormal corneal endothelial cells in affected men and women are consistent with an abnormal Descemet membrane, and the reduced cell density resembles the reduced podocyte numbers found in the Alport glomerulus.

Efecto de la lente fáquica ACR-128 sobre la tensión ocular y el endotelio corneal en las altas miopías / Effect of the ACR-128 phakic lens on ocular tension and the corneal endothelium in high myopia

RESUMEN Objetivo: Describir los efectos sobre la tensión ocular y el endotelio corneal con el implante de la lente fáquica ACR-128 para la corrección de la alta miopía. Métodos: Se realizó un estudio descriptivo, observacional, longitudinal y prospectivo en 60 ojos de 32 pacientes con miopía corregida con lente fáquica ACR-128. Se determinaron las complicaciones trans y posoperatorias, la presión intraocular, la densidad de las células endoteliales, el coeficiente de variabilidad y la hexagonalidad, así como la posición de la lente. El análisis estadístico se realizó con la Prueba T para datos pareados, con una significación del 95 por ciento. Resultados: La edad media fue de 27,41 ± 5,91 años y el 68,75 por ciento correspondió al sexo femenino. El equivalente esférico preoperatorio promedio fue de -11,54 ± 3,20 dioptrías. Resultó sin complicaciones transoperatorias el 100 por ciento; las posoperatorias inmediatas fueron de 93,33 por ciento y las mediatas y tardías del 95,00 por ciento. No hubo diferencias significativas entre el pre y el posoperatorio en la tensión ocular (p=0,2570); la densidad endotelial fue p= 0,0928; el coeficiente de variación p= 0,889 y la hexagonalidad (p= 0,0957). Conclusiones: El implante de la lente fáquica ACR-128 para la corrección de las altas miopías es un procedimiento seguro, al ofrecer escasas complicaciones y mínimos efectos en la tensión ocular y en el endotelio corneal(AU)

ABSTRACT Objective: Describe the effects of ACR-128 phakic lens implantation for high myopia correction on ocular tension and the corneal endothelium. Methods: An observational descriptive longitudinal prospective study was conducted of 60 eyes of 32 patients with myopia corrected with the ACR-128 phakic lens. Determination was made of intra- and postoperative complications, intraocular pressure, endothelial cell density, variability and hexagonality quotient, and lens position. Statistical analysis was based on the paired T-test with a significance level of 95 percent. Results: Mean age was 27.41 ± 5.91 years and 68.75 percent of the patients were female. Mean preoperative spherical equivalent was -11.54 ± 3.20 diopters. Complications were none in the intraoperative period, 93.33 percent in the immediate postoperative period and 95.00 percent mid- or long-term. No significant differences were found between the pre- and postoperative periods concerning ocular tension (p= 0.2570). Endothelial cell density was p= 0.0928, the variability quotient p= 0.889 and hexagonality p= 0.0957. Conclusions: ACR-128 phakic lens implantation for correction of high myopia is a safe procedure causing few complications and minimal effects on ocular tension and the corneal endothelium(AU)

Distrofia polimorfa posterior, presentación de un caso y análisis de la literatura / Posterior polymorphous dystrophy, case report and literature review

CASO CLÍNICO: La distrofia polimorfa posterior (DPP) es una distrofia corneal rara de transmisión autosómica dominante. Las estructuras corneales afectadas en esta distrofia son la membrana de Descemet y el endotelio. Se presenta el caso clínico de una mujer de 47 años sin antecedentes de importancia, con hallazgos típicos de DPP (lesiones vesiculares y en banda a nivel del endotelio y Descemet posterior). DISCUSIÓN: Encontramos que las manifestaciones clínicas en nuestra paciente son muy similares a los casos reportados en otras poblaciones. La ausencia de antecedentes heredofamiliares no descarta el diagnóstico de DPP puesto que esta enfermedad generalmente cursa asintomática

CASE REPORT: Posterior Polymorphous Dystrophy (DPP) is a rare posterior corneal dystrophy that is genetically transmitted as autosomal dominant. Corneal structures affected in this dystrophy are Descemet membrane and the endothelium. A case is presented on a 47 years old woman with no relevant history, with typical findings of DPP (vesicular and band lesions at the endothelium and posterior Descemet). DISCUSSION: To our knowledge there are no reported cases of DPP in Latin-American patients in the literature. The clinical manifestations in our patient were found to be very similar to the cases reported in other populations

Síndrome de Chandler / Chandler's syndrome

El síndrome de Chandler es una de las variaciones clínicas del síndrome iridocorneoendotelial, donde el denominador común es una alteración del endotelio corneal cuyo diagnóstico es, en ocasiones, muy difícil de realizar por la complejidad y la variabilidad de sus signos y síntomas. Se presenta una paciente de 67 años con disminución importante de la visión del ojo izquierdo. A la exploración existía un edema corneal severo, una midriasis pupilar, una corectopia leve hacia el sector temporal con tracción iridiana hacia el ángulo y sinequias anteriores angulares en el lado de la corectopia. La realización de un recuento endotelial demostró alteraciones cuali y cuantitativas del endotelio en el ojo izquierdo. Se concluyó que la microscopia especular es fundamental para el diagnóstico y la evaluación en casos sospechosos de síndrome de Chandler(AU)

Chandler's syndrome is a clinical variant of the iridocorneal endothelial syndrome in which the common aspect is the altered corneal endothelium that is sometimes very difficult to be diagnosed on account of the complexity and variability of signs and symptoms. This article was aimed at showing the effectiveness of specular microscopy for diagnosis. Here is a 67 years-old female patient who had significant reduction of vision in her left eye. On examination, there were observed severe corneal edema, pupillary mydriasis, mild corectopia towards the temporal sector with angled iridal traction and anterior angle synechias on the corectopia side. The endothelial counting revealed qualitative and quantitative alterations in the left eye. It was concluded that the specular microscopy is the key to diagnosis and assessment of suspected Chandler's syndrome cases(AU)

Síndrome de Chandler / Chandler's syndrome

El síndrome de Chandler es una de las variaciones clínicas del síndrome iridocorneoendotelial, donde el denominador común es una alteración del endotelio corneal cuyo diagnóstico es, en ocasiones, muy difícil de realizar por la complejidad y la variabilidad de sus signos y síntomas. Se presenta una paciente de 67 años con disminución importante de la visión del ojo izquierdo. A la exploración existía un edema corneal severo, una midriasis pupilar, una corectopia leve hacia el sector temporal con tracción iridiana hacia el ángulo y sinequias anteriores angulares en el lado de la corectopia. La realización de un recuento endotelial demostró alteraciones cuali y cuantitativas del endotelio en el ojo izquierdo. Se concluyó que la microscopia especular es fundamental para el diagnóstico y la evaluación en casos sospechosos de síndrome de Chandler(AU)

Chandler's syndrome is a clinical variant of the iridocorneal endothelial syndrome in which the common aspect is the altered corneal endothelium that is sometimes very difficult to be diagnosed on account of the complexity and variability of signs and symptoms. This article was aimed at showing the effectiveness of specular microscopy for diagnosis. Here is a 67 years-old female patient who had significant reduction of vision in her left eye. On examination, there were observed severe corneal edema, pupillary mydriasis, mild corectopia towards the temporal sector with angled iridal traction and anterior angle synechias on the corectopia side. The endothelial counting revealed qualitative and quantitative alterations in the left eye. It was concluded that the specular microscopy is the key to diagnosis and assessment of suspected Chandler's syndrome cases(AU)

Successful Descemet stripping endothelial keratoplasty in congenital hereditary endothelial dystrophy.

PURPOSE: To report successful Descemet stripping endothelial keratoplasty (DSEK) in a patient with congenital hereditary endothelial dystrophy (CHED). METHODS: A 19-year-old boy presented with complaints of decreased vision, hazy corneas, and nystagmus since birth. Six months prior, the right eye had undergone penetrating keratoplasty. In the left eye, he was planned for DSEK. RESULTS: Successful Descemet membrane (DM) scoring and stripping was achieved with a reverse Sinskey hook after trypan blue staining. Manually dissected posterior stromal donor tissue was transplanted using Busin glide. Corneal edema resolved completely with a final best-corrected visual acuity of 20/100 at 6 months. Serial anterior segment optical coherence tomography scans showed maximum decrease in stromal thickness in the first month. Despite resolution of corneal edema, mild stromal haze persisted, which decreased with time. Histopathology of removed DM showed thickened DM and absence of endothelial cells which was suggestive of CHED. CONCLUSIONS: To the best of our knowledge, this is the first reported case of successful DSEK in a patient with CHED.

Non-invasive assessment of corneal endothelial permeability by means of electrical impedance measurements.

The permeability of the corneal endothelial layer has an important role in the correct function of the cornea. Since ionic permeability has a fundamental impact on the passive electrical properties of living tissues, here it is hypothesized that impedance methods can be employed for assessing the permeability of the endothelial layer in a minimally invasive fashion. Precisely, the main objective of the present study is to develop and to analyze a minimally invasive method for assessing the electrical properties of the corneal endothelium, as a possible diagnostic tool for the evaluation of patients with endothelial dysfunction. A bidimensional model consisting of the main corneal layers and a four-electrode impedance measurement setup placed on the epithelium has been implemented and analyzed by means of the finite elements method (FEM). In order to obtain a robust indicator of the permeability of the endothelium layer, the effect of the endothelium electrical properties on the measured impedance has been studied together with reasonable variations of the other model layers. Simulation results show that the impedance measurements by means of external electrodes are indeed sufficiently sensitive to the changes in the electrical properties of the endothelial layer. It is concluded that the method presented here can be employed as non-invasive method for assessing endothelial layer function.

Absence of phenotype-genotype correlation of patients expressing mutations in the SLC4A11 gene.

PURPOSE: The purposes of this study were to describe the clinical characteristics of corneal patients with mutations in the SLC4A11 gene and to determine if these characteristics could be correlated with specific genetic mutations. METHODS: A retrospective case series review was conducted. Baseline demographic data, including gender, age at diagnosis of congenital hereditary endothelial dystrophy, family history, and pedigree information, were obtained. Information from clinical examination, including intraocular pressure, ultrasonic pachymetry, best spectacle-corrected visual acuity, axial length, and slit-lamp biomicroscopic evaluation, including corneal diameter and fundus examination, were also documented from the notes. History of corneal surgery was also recorded. Hearing loss was assessed by audiometry. Genetic analysis was performed by polymerase chain reaction amplification and sequencing. RESULTS: Seven patients were identified. Four of the seven had associated hearing loss; all of the patients had undergone or were awaiting penetrating keratoplasty to one or both eyes. No correlation could be reached between the ocular phenotype and the gene mutation in this small sample. Individuals with the same mutation had different degrees of hearing loss within their respective families. CONCLUSIONS: Corneal endothelial cells are more vulnerable to defects in the functional activity of SLC4A11 than cells of the striae vascularis of the inner ear. Both congenital hereditary endothelial dystrophy 2 and Harboyan syndrome have similar ocular phenotypes, ie, diffuse bilateral corneal edema present at birth or within the neonatal period; hence, audiometry must be performed to differentiate the two conditions.

[Posterior polymorphous corneal dystrophy--case report]. / Dystrofia polimorficzna tylna rogówki--opis przypadku.

Posterior polymorphous corneal dystrophy (PPCD) is a rare, bilateral, congenital disorder. It affects endothelial cells and Descemet's membrane. Slit lamp examination of PPCD shows characteristic bilateral endothelial bands, vesicles, and polymorphous opacities at the level of Descemet's membrane and endothelium, which can be accompanied by iridocorneal peripheral adhesions, iris atrophy, and corectopia. The clinical phenotype of PPCD can vary from relatively benign Descemet's thickening to severe progression towards vision loss from corneal edema or consecutive glaucoma. We present a case report of a 7-years old male patient with left eye corneal edema. Diagnosis of PPCD is made by slit-lam examination accompanied by anterior segment optical coherence tomography (AS OCT), and specular microscopy examination. Examination also revealed corneal changes in left eye of 32-years old patient's mother.

Queratoplastia endotelial de membrana de Descemet (DMEK): resultados a dos años / Descemet membrane endothelial keratoplasty (DMEK): Two-year results

Objetivo: Describir los resultados, dos años despuésde realizar una queratoplastia endotelial demembrana de Descemet (DMEK: Descemet membraneendothelial keratoplasty), para el tratamientode alteraciones del endotelio corneal.Métodos: Estudio clínico prospectivo no randomizado.En 10 pacientes con distrofia endotelial deFuchs o queratopatía bullosa, se practicó unaDMEK. A través de una incisión de 3,5 mm en córneaclara, la membrana de Descemet (MD) delreceptor fue desprendida del estroma posterior enpresencia de aire. Un disco de 9 mm de diámetroenrollado de MD donante preservada, fue insertadoen la cámara anterior del receptor, posicionado encontacto con el estroma posterior corneal y aseguradoen su posición mediante el llenado completode la cámara anterior con aire durante 30 minutos.Resultados: Tres ojos mostraron un desprendimientocompleto del tejido donante, por lo que fueronsometidos posteriormente a una queratoplastiaendotelial con «pelado» de la MD (DSEK: Descemet stripping endothelial keratoplasty). En los sieteojos restantes, se observó una agudeza visual mejorcorregida (AVMC) ≥ a 0,7 en 3 ojos (43%) en el primermes, en 5 ojos (71%) a los seis meses, y en seisojos (86%) al primer y segundo años. A los seismeses, la densidad celular endotelial media fue de2039 (DS: 373) cél/mm2 (n=7), al año de 1925 (DS:267 cél/mm2 (n=7) y a los 2 años de 1730 (DS: 400)cél/mm2 (n=6).Conclusión: DMEK podría proporcionar una recuperaciónrápida y casi completa de la visión. Debidoa que el tejido donante puede ser obtenido a partirde anillos córneo-esclerales donantes, el procedimientopodría ser fácilmente accesible para lamayoría de los cirujanos corneales(AU)

Purpose: To report the two-year results of Descemetmembrane endothelial keratoplasty (DMEK)for managing corneal endothelial disorders.Methods: Non-randomized prospective clinicaltrial. A DMEK was performed in ten patients withFuchs’ endothelial dystrophy or bullous keratopathy.A 3.5 mm clear corneal incision was madeand «under air» DM was stripped off from the posteriorstroma. A 9.0 mm diameter, organ cultureddonor DM roll was inserted into a recipient anteriorchamber, positioned into the posterior stroma andsecured by completely filling the anterior chamberwith air for 30 minutes.Results: Three eyes showed complete detachmentof the tissue; this was managed by a secondary Descemetstripping endothelial keratoplasty procedure.The remaining seven eyes had a best correctedvisual acuity of ≥ 0.7 in three eyes (43%) at onemonth, in five eyes (71%) at six months, and in sixeyes (86%) at one and two years. At six months, theendothelial cell density averaged 2039 (±373) cells/mm2 (n=7), at one year 1925 (±267) cells/mm2(n=7) and at two years 1730 (±400) cells/mm2(n=6).Conclusions: DMEK may provide quick andnearly complete visual rehabilitation. Since thedonor tissue can be stripped from donor corneoscleralrims, the procedure may be readily accessibleto most corneal surgeons(AU)

Dominant inhibition of lens placode formation in mice.

The lens in the vertebrate eye has been shown to be critical for proper differentiation of the surrounding ocular tissues including the cornea, iris and ciliary body. In mice, previous investigators have assayed the consequences of molecular ablation of the lens. However, in these studies, lens ablation was initiated (and completed) after the cornea, retina, iris and ciliary body had initiated their differentiation programs thereby precluding analysis of the early role of the lens in fate determination of these tissues. In the present study, we have ablated the lens precursor cells of the surface ectoderm by generation of transgenic mice that express an attenuated version of diphtheria toxin (Tox176) linked to a modified Pax6 promoter that is active in the lens ectodermal precursors. In these mice, lens precursor cells fail to express Sox2, Prox1 and alphaA-crystallin and die before the formation of a lens placode. The Tox176 mice also showed profound alterations in the corneal differentiation program. The corneal epithelium displayed histological features of the skin, and expressed markers of skin differentiation such as Keratin 1 and 10 instead of Keratin 12, a marker of corneal epithelial differentiation. In the Tox176 mice, in the absence of the lens, extensive folding of the retina was seen. However, differentiation of the major cell types in the retina including the ganglion, amacrine, bipolar and horizontal cells was not affected. Unexpectedly, ectopic placement of the retinal pigmented epithelium was seen between the folds of the retina. Initial specification of the presumptive ciliary body and iris at the anterior margins of the retina was not altered in the Tox176 mice but their subsequent differentiation was blocked. Lacrimal and Harderian glands, which are derived from the Pax6-expressing surface ectodermal precursors, also failed to differentiate. These results suggest that, in mice, specification of the retina, ciliary body and iris occurs at the very outset of eye development and independent of the lens. In addition, our results also suggest that the lens cells of the surface ectoderm may be critical for the proper differentiation of the corneal epithelium.

Coexistent congenital hereditary endothelial dystrophy and congenital glaucoma.

PURPOSE: To retrospectively evaluate the coexistence of congenital glaucoma with congenital hereditary endothelial dystrophy. METHODS: Ten infants presented to our hospital with diffuse corneal edema and bilaterally elevated intraocular pressure (IOP). These patients were diagnosed with congenital glaucoma. All patients underwent trabeculotomy with trabeculectomy for control of IOP. Although IOP was normalized in all patients, corneal edema persisted. These patients underwent penetrating keratoplasty, and the buttons were subjected to histopathologic examination. RESULTS: The corneal grafts remained clear in all patients. The histopathologic examination of the excised corneal buttons showed diffuse stromal edema, loss of the endothelial cell layer, and thickening of the posterior non-banded portion of the Descemet membrane, suggestive of congenital hereditary endothelial dystrophy. CONCLUSIONS: Congenital hereditary endothelial dystrophy may coexist with congenital glaucoma. This combination should be suspected where persistent and total corneal opacification fails to resolve after normalization of IOP.

Immunohistochemical characterization of cytokeratins in the abnormal corneal endothelium of posterior polymorphous corneal dystrophy patients.

Posterior polymorphous corneal dystrophy (PPCD) is a hereditary bilateral disorder affecting Descemet's membrane and the endothelium. The aim of the present study was to determine the spectrum of cytokeratin (CK) expression in cells on the posterior surface of the cornea in PPCD patients. Ten corneal buttons and one specimen of the trabecular meshwork (TM) from PPCD patients who underwent graft or glaucoma surgery were used, as well as six corneal buttons and two TM specimens obtained from healthy donors as controls. Cryosections were fixed and indirect immunofluorescent staining was performed using antibodies directed against a wide spectrum of cytokeratins (CKs). The number of positive cells and the intensity of the staining were assessed using fluorescent microscopy. All 10 PPCD corneal specimens had areas of endothelium displaying typical endothelial morphology as well as areas consisting of layers two to six cells thick with both flat endothelial-like cells and polygonal cells with round nuclei and a large cytoplasm. Both of these morphologically distinct cell types showed strong immunostaining for CK7, CK19, CK8 and CK18, while weaker positive signals were observed for CK1, CK3/12, CK4, CK5/6, CK10, CK10/13, CK14, CK16 and CK17. PPCD endothelium was completely negative for CK2e, CK9, CK15, and CK20. Focal positivity was detected in PPCD TM for CK4, CK7 and CK19. CK8 and CK18 were the only CKs expressed in control endothelium. PPCD and control epithelium displayed similar staining patterns. The distinct positivity for CK3/12, CK4, CK5/6, CK10/13, CK14, CK16 and CK17 was observed in aberrant PPCD endothelium for the first time. We demonstrate that the abnormal endothelium of PPCD patients expresses a mixture of CKs, with CK7 and CK19 predominating. In terms of CK composition, the aberrant PPCD endothelium shares features of both simple and squamous stratified epithelium with a proliferative capacity. The wide spectrum of CK expression is most probably not indicative of the transformation of endothelial cells to a distinct epithelial phenotype, but more likely reflects the modified differentiation of metaplastic epithelium.

Perinatal ablation of the mouse lens causes multiple anterior chamber defects.

PURPOSE: The purpose of this study was to reassess the role of the lens as an "embryonic organizer" of ocular tissues. METHODS: We ablated the lens in mice by lens-specific expression of an attenuated version of diphtheria toxin A subunit(Tox176) driven by a modified crystallin promoter. Alterations in the differentiation programs of ocular tissues were examined by hematoxylin and eosin staining, in situ hybridization, and immunohistochemistry. RESULTS: Transgenic mice in the family OVE1757 exhibited severe microphakia. Apoptotic lens fibers were seen by embryonic day 15 (E15) and the lenses were completely ablated by post natal day 8. Multiple defects were seen in the anterior chamber. Corneal endothelial cells did not differentiate properly. The mesenchymal cells that would normally give rise to the endothelial layer were found to express N-cadherin, but they failed to form tight junctions and undergo a mesenchymal-to-epithelial transition. Although early specification of the presumptive ciliary body and iris was detected, subsequent differentiation of the iris was blocked. No dramatic changes were seen in the development of the retina. CONCLUSIONS: These results support the hypothesis that an intact lens is essential for proper differentiation of both the corneal endothelium and the iris and that the lens "organizes" the development of tissues in the anterior chamber.

Ultrasound biomicroscopy of Chinese eyes with iridocorneal endothelial syndrome.

AIM: To document the ultrasound biomicroscopic (UBM) findings in Chinese patients with iridocorneal endothelial (ICE) syndrome. METHODS: 21 patients with ICE syndrome and 15 normal subjects underwent UBM. UBM findings of anterior segment were compared between normal subjects and three clinical types of ICE syndrome: progressive iris atrophy (PIA), Chandler's syndrome (CS), and Cogan-Reese syndrome (CRS). RESULTS: Central anterior chamber depth was significantly less in patients with ICE syndrome (2.25 (SD 0.32) mm) than in normal subjects (2.76 (0.32) mm). Peripheral anterior synechiae were observed in all the ICE patients by UBM. Three out of four CRS subjects showed an "arborised" shape of iridocorneal angle. Two eyes out of 10 with CS presented bridge-shaped synechiae. A membrane-like mound was observed in iridocorneal angle in two patients: one with CRS and one with CS. UBM was found to be more effective in detecting peripheral anterior synechiae (PAS) and iris atrophy than slit lamp microscopy and gonioscopy, mainly because of corneal oedema in patients with CS. Four out of 11 patients with unilateral ICE syndrome had shallow or closed anterior chamber angles in their fellow eyes. Two of them successfully responded to laser peripheral iridotomy. CONCLUSIONS: UBM is an effective method to reveal the anterior segment features and provides a useful tool in the diagnosis of ICE syndrome. Different subtypes of ICE syndrome may have different UBM manifestations. UBM can help to identify angle closure in the fellow eye of unilateral ICE syndromes.

Corneal endothelial abnormalities associated with thalidomide toxicity.

PURPOSE: To describe bilateral corneal endothelial abnormalities associated with thalidomide toxicity. METHODS: Observational case report. RESULTS: A 30-year-old man, born with bilateral hypoplastic upper limb defects (phocomelia) caused by thalidomide toxicity, presented with bilateral symmetrical corneal endothelial changes resembling guttata without corneal edema. Pachymetry, specular microscopy, and confocal microscopy were performed. Biomicroscopy findings over a 10-year follow-up showed no changes. CONCLUSIONS: Nonprogressive bilateral corneal endothelial changes resembling cornea guttata should possibly be included in the ocular manifestations of thalidomide toxicity. We postulate that thalidomide may have affected the migration and development of the mesenchymal neural crest cells, which are the developmental precursors of the corneal endothelium and stroma.