Proteoglycan distribution in the corneas of individuals with bullous keratopathy.
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Collagen↗
Biomedical subjects
A J Quantock
Publications and source records attributed to A J Quantock.
Macular corneal dystrophy: reduction in both corneal thickness and collagen interfibrillar spacing.
The interfibrillar spacing of collagen fibrils was measured at twenty different positions across a macular dystrophy cornea using synchrotron X-ray diffraction. Unlike previous work of this type the cornea had not been frozen for storage. The spacings were all significantly lower than the spacings which existed at similar positions across a normal adult human cornea. This close-packing of collagen fibrils seems to be responsible for the reduced thickness of the central cornea in macular dystrophy. Neither the patient's serum or corneal tissue contained appreciable amounts of sulfated keratan sulfate, this classifies the disease as Type I macular corneal dystrophy.
Adult↗
Macular corneal dystrophy: the macromolecular structure of the stroma observed using electron microscopy and synchrotron X-ray diffraction.
The distribution of sulphated proteoglycans within the stromas of three patients (A,B,C) suffering from macular corneal dystrophy was studied using the specific dye Cuprolinic Blue in a 'critical electrolyte concentration' method. The corneas were examined using transmission electron microscopy and A and C were further studied by low-angle synchroton X-ray diffraction. Sera from all three patients were analyzed for the presence of keratan sulphate using a monoclonal antibody in an enzyme-linked immunosorbent assay. The serum from Patient A contained keratan sulphate, but the chains were thought to be shorter or less sulphate in their sera. Electron microscopy showed many electron-transparent lacunae randomly distributed throughout the specimens. The average collagen fibril diameter was normal but there were differences in packing between the specimens. Specimen A was closely-packed with most collagen fibrils in contact with their neighbours. Specimens B and C showed fewer regions of close packing; in most of the tissue the interfibrillar spacing appeared normal. Staining with Cuprolinic Blue revealed an unusual distribution of proteoglycans in some parts of the interfibrillar matrix, particularly in A, with 'small' proteoglycans running exclusively parallel to the collagen fibrils. Furthermore in A, and to a lesser extent in B and C, some lacunae were filled with clusters of abnormal sulphated proteoglycan filaments (of various sizes) which were chondroitinase ABC susceptible. Clearly defined regions, both within the lacunae and elsewhere, failed to stain with Cuprolinic Blue; this suggests an absence of sulphated proteoglycans within these areas. Equatorial X-ray diffraction of the wet tissues (A and C) gave values for the mean interfibrillar centre-to-centre separation of 43 +/- 2 nm in Specimen A and 52 +/- 3 nm in Specimen C. The differences observed in the serum keratan sulphate levels, the packing of the collagen fibrils and the distribution of chondroitin/dermatan sulphate proteoglycans confirm the heterogeneity that exists within the macular corneal dystrophies.
Chondroitin Sulfates↗
Axial electron density of human scleral collagen. Location of proteoglycans by x-ray diffraction.
The low angle meridional x-ray diffraction pattern from fresh human sclera was analyzed to ascertain if collagen-bound proteoglycans affect the axially-projected electron density distribution to the same extent as appears to occur in the cornea. The results showed that, unlike cornea, the electron density of the sclera is similar to that seen in rat tail tendon collagen. The proteoglycans were specifically stained using either Cuprolinic blue or Cupromeronic blue, both under critical electrolyte conditions. The tissue was then examined by electron microscopy and by low angle x-ray diffraction. The electron-optical observations suggested that proteoglycans associate with collagen near the d/e staining bands in the gap zone. A difference Fourier analysis from the x-ray results confirmed that these observations were not e.m. preparative artefacts and allowed a quantitative estimate to be made of the axial extent of the proteglycans in the wet tissue.
Animals↗
Wound healing in response to keratorefractive surgery.
Over one million Americans have undergone refractive keratoplasty since the introduction of radial keratotomy into the United States in 1978. There are now a number of alternative techniques available for reshaping the corneal surface to alter ocular refractive errors. Numerous technologic advances in the past decade now enable us to perform these procedures in a safer and more reliable fashion. The ability to control precisely the refractive outcome, however, continues to elude us and appears to be limited, in part, by interindividual variability in the wound healing response. Presently, we review the corneal wound healing response to various keratorefractive approaches and suggest some interventional strategies which might enable us to modulate more precisely our refractive results.
Animals↗
Comparison of the standard combined (bidirectional) radial keratotomy technique with the undercut technique in human donor eyes.
BACKGROUND: We evaluated the efficacy of a new radial keratotomy technique, using a diamond designed to undermine the central clear zone without incising superficial stroma. METHODS: An 8-incision radial keratotomy at a 3-mm central clear zone was performed on nine pairs of human donor globes. One eye of each pair was incised using the standard combined (bidirectional) technique diamond and the contralateral eye, using the undercut bidirectional technique diamond. Paired t-tests were used to compare changes in central corneal curvature between these two groups. Microscopic analysis of incision morphology was performed on four eyes. RESULTS: Corneal topography at the 1-, 3-, and 5-mm annular zones revealed corneal flattening of 7.70 +/- 1.50 diopters (D), 6.70 +/- 1.30 D, and 5.10 +/- 1.00 D, respectively, in the undercut bidirectional technique group versus 6.20 +/- 1.70 D, 5.30 +/- 1.50 D, and 4.00 +/- 1.20 D, respectively, in the standard bidirectional technique group (P < 0.01 for each annular zone). Light microscopy (serial sections) revealed an average incision depth of 80.9 +/- 3.9% in the undercut bidirectional technique group versus 72.7 +/- 4.5% in the combined group (P < 0.01). The undercut bidirectional technique incisions undermined the central clear zone for a distance of approximately 350 microns compared to about 140 microns for the standard bidirectional incisions. CONCLUSIONS: In the human cadaver eye, the undercut technique of radial keratotomy provided greater flattening than the standard bidirectional technique. The greater amount of flattening may result from greater central extension of the undercut incisions beneath the central clear zone, from greater incision depth, or from a combination of both factors.
Aged↗
Ultrastructure of picosecond laser intrastromal photodisruption.
PURPOSE: To investigate the ultrastructure of the corneal stroma after picosecond intrastromal photodisruption with a neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser. METHODS: We performed picosecond intrastromal photodisruption on six human eye-bank eyes using a lamellar technique. Thirty picosecond pulses at 1000 Hz and 20 to 25 mJ per pulse were placed in an expanding spiral pattern, the pulses separated by 15 microns. Three layers were placed in the anterior stroma, separated from each other by 15 microns. In addition, intrastromal radial and arcuate incisions were generated in two living rabbit eyes in a plane perpendicular to the corneal surface. After the procedure, the corneas were processed for scanning and transmission electron microscopy. RESULTS: Scanning electron microscopy of the eye-bank eyes demonstrated multiple, coalescing intrastromal cavities forming a layer oriented parallel to the corneal surface. These cavities had smooth inner walls. Transmission electron microscopy demonstrated tissue loss surrounding some cavities, with the terminated ends of collagen fibrils clearly evident. Other cavities were formed by separation of lamellae, with little evidence of tissue loss. A pseudomembrane was present along the margin of some cavities. Although there was occasional underlying tissue disruption along the border of a cavity, there was no evidence of thermal damage or tissue necrosis. The perpendicular photodisruptions demonstrated intrastromal cleavage of corneal collagen similar to diamond-knife incisions, with the exception of intact overlying Bowman's and epithelial layers. CONCLUSION: Intrastromal photodisruption with a Nd:YLF picosecond laser induced no thermal necrosis or coagulative change in the region of tissue interaction. Lamellar intrastromal photodisruption demonstrated both tissue loss and lamellar separation when performed with the current treatment parameters, possibly limiting ablation efficiency and predictability.
Animals↗
Picosecond laser in situ keratomileusis with a 1053-nm Nd:YLF laser.
BACKGROUND: Excimer laser in situ keratomileusis requires a microkeratome to generate an anterior corneal flap, plus an excimer laser to ablate the underlying stromal tissue. In this paper we introduce the concepts of laser flap formation and in situ keratomileusis using a picosecond laser. METHODS: A neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser with a plano-plano quartz applanation lens was used to generate various patterns of intrastromal photodisruption in human donor eyes to fashion anterior corneal flaps and generate intrastromal lenticules. RESULTS: Smooth intrastromal dissections, 6 mm in diameter, were generated 160 microns below the corneal surface when the laser delivered pulses at 1 kHz with energies of either 40 microJ/pulse or 60 microJ/pulse, placed 20 microns apart in an expanding spiral. This enabled us to fashion anterior corneal flaps. The ease of the surgery and quality of the dissection corresponded well, and it was evident that both deteriorated noticeably when the laser pulses were separated by 25 microns or 30 microns, regardless of pulse energy. Using 40 microJ laser pulses placed 20 microns apart we also created a 5-mm diameter, 320 microns thick (130 microns-450 microns deep) stromal lenticule below a corneal flap that was easily extracted when the flap was raised. CONCLUSIONS: Anterior corneal flaps were easily fashioned using a Nd:YLF laser. Picosecond laser in situ keratomileusis with a Nd:YLF laser could offer a favorable alternative to combined microkeratome/excimer laser in situ keratomileusis.
Cornea↗
Organization of collagen in the lyophilized cornea.
PURPOSE: To investigate the organization of collagen fibrils in the lyophilized cornea. METHODS: Freshly harvested porcine corneas (n = 10) were lyophilized and examined by synchrotron x-ray diffraction and transmission electron microscopy. RESULTS: Collagen fibrils are highly compacted in lyophilized corneas. They become more widely spaced when the tissue is rehydrated, however, the distribution of imbibed water throughout the stroma is not necessarily homogeneous within an individual cornea, nor is it always similar in specimens that have been rehydrated to similar levels. In lyophilized corneas, the mean center-to-center interfibrilar spacing of the regularly arranged collagen reaches levels found in freshly thawed porcine corneas (between 74% and 78% water by weight) when between 74.3% and 81.6% of the rehydrated lyophilized cornea's weight is water. CONCLUSION: Regularly arranged collagen fibrils are able to reapproximate their original spacings if lyophilized corneal tissue is rehydrated, although the manner in which imbibed water is distributed is somewhat unpredictable.
Animals↗
Endothelial cell surface-associated keratan sulfate after excimer laser photoablation of the anterior rabbit cornea.
PURPOSE: The expression of keratan sulfate on the surfaces of corneal endothelial cells is altered when the cells are responding to injury. The purpose of this study was to investigate whether excimer laser surgery affected corneal endothelial cells and the levels of keratan sulfate associated with them. METHODS: We performed 14 bilateral, transepithelial phototherapeutic keratectomies in rabbits using a Nidek EC-5000 excimer laser. Ablations were 6 mm in diameter and 50 microm, 150 microm, or 240 microm deep. At various times following surgery the endothelium was immunolabeled for keratan sulfate and examined by scanning electron microscopy. Four untreated corneas were also examined. RESULTS: Three days after surgery, endothelial cells were not flat but were rounded or domed, a finding that was more pronounced after deeper ablations. No rounded cells, however, were seen at post-operative day 12. Keratan sulfate immunolabel was elevated on endothelial cells 3 days after surgery. By postoperative day 36, its expression was normal under the 50-microm ablations, but remained elevated under one of two 240-microm ablations. CONCLUSIONS: Corneal endothelial cells take on a rounded appearance in the early stages after excimer laser photoablations in rabbits, especially after deeper ablations. The apical surface of the endothelium also transiently expresses elevated levels of cell surface-associated keratan sulfate following surgery. These changes appear to be responses to some aspect of the surgery, and may have physiological implications.
Animals↗
Electron microscopic evaluation of intrastromal corneal rings explanted from nonfunctional human eyes.
BACKGROUND: Intrastromal corneal rings (ICRs) often exhibit small deposits in association with their suture holes. We assessed the morphology of four such deposits. METHODS: Four ICRs, explanted from nonfunctional human eyes, were examined by scanning electron microscopy and transmission electron microscopy. RESULTS: The surface of the suture hole deposits consisted of a disorganized convolution of collagenous lamellae. Within individual lamellae, however, the collagen fibrils tended to orientate parallel with one another. The deposits consisted of an amorphous material interspersed with curved cellular processes, collagen fibrils of variable diameter, and proteoglycan macromolecules. CONCLUSIONS: We propose that the mechanism which regulates stromal remodeling is amended in the region of the ICR suture holes. Due to their location, suture hole deposits have no optical significance; however, evaluation of their morphology provides insights into the wound-healing properties of the corneal stroma following ICR insertion.
Blindness↗