Relationships of the masked gulls.-Although molecular biologists may have useful information for ... more Relationships of the masked gulls.-Although molecular biologists may have useful information for ornithologists, they usually overlook the possibility that ornithologists might also be able to tell them something. From work in the fi eld and with museum specimens, I know most of the smaller, more or less masked, southern gulls whose affi nities Given et al. (2005) analyzed, and I have some problems with their conclusion that these species are all related to each other and also to the northern Black-headed Gull (Larus ridibundus). First, Given et al. are not the fi rst to suggest that the Black-headed Gull has a southern relative. Murphy (1936:1084) wrote of the Brown-hooded Gull (L. maculipennis): This Patagonian gull is so closely related to the [Black-headed] Gull of Europe that Hellmayr (1932, 412) believes the relationship between the two might possibly be regarded as subspecifi c. Aplin (1894, 211) states, furthermore, that in voice and actions the Argentine bird is much like ridibundus, a fact that had also been noted by Darwin.
Background: Central corneal thickness greater than 0.520 mm causes true intraocular pressure to b... more Background: Central corneal thickness greater than 0.520 mm causes true intraocular pressure to be overestimated when the technique of applanation tonometry is used to measure intraocular pressure. Objective: To compare the corneal thickness measurements of patients enrolled in a study of ocular hypertension with those of age-matched control subjects with normal intraocular pressure. Methods: Central corneal pachymetry using an optical pachymeter was performed on each study subject (n=55) at baseline and in an independent sample of control subjects. A 2 sample, 2-tailed t test was used to compare the 2 populations. Results: The patients with ocular hypertension had significantly higher mean corneal thickness measurements (mean±SD, 0.594±0.037 mm) than the control group (0.563±0.027 mm) (PϽ.001). Conclusion: Corneal thickness may be a confounding factor in the measurement of intraocular pressure, and this may modify the risk for progression to glaucoma in patients with ocular hypertension.
Purpose-To compare subbasal nerve densities estimated from images recorded by the Tandem Scanning... more Purpose-To compare subbasal nerve densities estimated from images recorded by the Tandem Scanning and the ConfoScan 4 confocal microscopes. Methods-Confocal microscopy was used to estimate subbasal nerve density in 62 corneas of 40 subjects (18 corneas of 18 normal subjects and 44 corneas of 22 patients between 1 and 12 months after LASIK) At each examination, corneas were scanned first by using Tandem Scanning and then by using a ConfoScan 4 confocal microscope. Subbasal nerves from 2 to 4 scans per cornea were traced by using a semi-automated nerve analysis program. Nerve density was expressed as total nerve length divided by the sample area (µm/mm 2). Differences in nerve density between instruments were examined by using paired tests. Results-In normal corneas, subbasal nerve density was 10,658 ± 5,581 µm/mm 2 (mean ± SD) with the ConfoScan 4 and 5,534 ± 1,850 µm/mm 2 with the Tandem Scanning microscope (P<0.0001). One to 12 months after LASIK, mean subbasal nerve density was 2,477 ± 3,514 µm/mm 2 estimated with the ConfoScan 4 and 844 ± 983 µm/mm 2 estimated with the Tandem Scanning (P=0.0003). Estimates of nerve density were correlated between instruments (r=0.71, P<0.0001), although the mean difference between instruments was 2,308 ± 3,885 µm/mm 2 (P<0.0001). Conclusions-Mean subbasal nerve density estimated with the ConfoScan 4 was 2 to 3 times higher than density estimated with the Tandem Scanning confocal microscope. These differences must be considered when comparing subbasal nerve densities between studies that use different confocal microscopes.
Investigative Ophthalmology & Visual Science, May 1, 2005
ABSTRACT To determine changes in keratocyte density up to 3 years after LASIK. Prospective, nonra... more ABSTRACT To determine changes in keratocyte density up to 3 years after LASIK. Prospective, nonrandomized, comparative trial. Seventeen eyes of 11 patients received LASIK with a planned 180-microm flap to correct refractive errors between -2.0 diopters (D) and -11.0 D (mean, -6.56+/-2.44). Corneas were examined by using confocal microscopy before LASIK and 1, 3, 6, 12, 24, and 36 months after LASIK. Bright objects that resembled keratocyte nuclei were manually counted by a masked observer. Cell densities were determined in anterior and posterior halves of the stromal flap, anterior and posterior halves of the 100-microm-thick layer immediately behind the ablation (retroablation layer), and the posterior third of the stroma. The region of stroma that was ablated (as measured 1 month after LASIK) was omitted from preoperative analysis. Cell densities after LASIK were compared (using1-factor repeated-measures analysis of variance) with densities in the corresponding layer of the normal preoperative stroma (which served as its own control). Corneal keratocyte density. Before LASIK, keratocyte densities in the anterior and posterior stromal flap and the anterior retroablation layer were 34 818+/-5108 cells/mm(3) (mean +/- SD), 25 390+/-4045 cells/mm(3), and 21 328+/-2980 cells/mm(3), respectively, and densities in these layers decreased 14% to 20% at 1 month after LASIK (P&lt;0.001). Keratocyte densities in these layers remained stable at 3 and 6 months, and then gradually decreased further (P&lt;0.001) to 26% to 36% below pre-LASIK densities by 3 years. Keratocyte densities in the remaining stromal layers did not change after LASIK. Keratocyte densities in the stromal flap and in the anterior retroablation layer decrease during the first 6 months after LASIK and then decrease further during the next 2.5 years. Further studies on these patients and others are warranted to confirm these findings and learn their significance.
Salmonella tymphimurium enteritis; 0.36 Positive Periphlebitis, especially of vena miliary patter... more Salmonella tymphimurium enteritis; 0.36 Positive Periphlebitis, especially of vena miliary pattern on chest X-ray nasalis superior, both eyes 5, M, 13 Interstitial pneumonia Unknown Positive Periphlebitis of vena temporalis inferior, L.E. 6, M, 41 Bilateral parotitis; persistent 0.30 Positive Periphlebitis, both eyes pulmonary infiltrates 'Measured by an indirect immunofluorescence technique with monoclonal antibodies. 'Detected by an enzyme-linked immunosorbent assay using disrupted HTLV-1I1 as antigen in which antibody was considered to be detected if the absorbance ratio for the test serum compared to that of a standard negative serum was> 8.0
Purpose: To measure changes in keratocyte density up to 5 years after photorefractive keratectomy... more Purpose: To measure changes in keratocyte density up to 5 years after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Methods: This was a prospective, nonrandomized clinical trial. Eighteen eyes of 12 patients received PRK to correct a mean refractive error of -3.73 +/- 1.30 D, and 17 eyes of 11 patients received LASIK to correct a mean refractive error of -6.56 +/- 2.44 D. Corneas were examined by using confocal microscopy before and 6 months, 1 year, 2 years, 3 years, and 5 years after the procedures. Keratocyte densities were determined in five stromal layers in PRK patients and in six stromal layers in LASIK patients. Differences between preoperative and postoperative cell densities were compared by using Bonferroni-adjusted paired t tests. Results: After PRK, keratocyte density in the anterior stroma was decreased by 39%, 42%, 45%, and 47% at 6 months, 2 years, 3 years, and 5 years, respectively (P < .001). At 5 years, keratocyte density was decreased by 20% to 24% in the posterior stroma (P < .05). After LASIK, keratocyte density in the stromal flap was decreased by 22% at 6 months (P < .02) and 37% at 5 years (P < .005). Keratocyte density in the anterior retroablation zone was decreased 18% (P < .005) at 1 year and 43% (P < .005) at 5 years. At 5 years, keratocyte density was decreased by 19% to 22% (P < .05) in the posterior stroma. Conclusions: Keratocyte density is decreased in the anterior stroma after PRK and in the stromal flap and the retroablation zone after LASIK for up to 5 years. Posterior stromal keratocyte deficits are first noted at 5 years.
Purpose: To determine central keratocyte and subbasal nerve densities after penetrating keratopla... more Purpose: To determine central keratocyte and subbasal nerve densities after penetrating keratoplasty (PK) in clear grafts and in grafts with late endothelial failure (LEF). Methods: Ninety-nine clear grafts of 74 patients and 21 grafts with LEF in 19 patients were examined by confocal microscopy at 1 to 31 years after PK. Keratocyte density and number of keratocytes in a full-thickness column of stroma with frontal area of 1 mm(2) were determined from images. Subbasal nerve fiber bundle density was measured in the central cornea as the visible length of nerve per frame area. Comparisons were made to normal corneas. Results: Full-thickness keratocyte density in clear grafts (22,101 +/- 3,799 cells/mm(3), mean +/- SD, n = 99) was lower than in normal corneas (26,610 +/- 3,683 cells/mm(3), n = 63, P < .001) but did not differ from grafts with LEF (21,268 +/- 3,298 cells/mm(3), n = 12, P = .47). The number of keratocytes in clear grafts (10,325 +/- 1,708 cells, n = 99) was lower than in normal corneas (11,466 +/- 1,503 cells, n = 63, P < .001) but did not differ from grafts with LEF (10,778 +/- 1,760 cells, n=12, P = .39). Median subbasal nerve density in clear grafts (150 microm/mm(2), n = 94) was lower than in normal corneas (7,025 microm/mm(2), n = 76, P < .001), and nerve recovery correlated with time after PK (r = 0.36, P < .001, n = 94). Conclusions: Keratocyte density and number of keratocytes are decreased in penetrating grafts compared to normal corneas, but not compared to grafts with LEF. Subbasal nerve density does not recover to normal through 30 years after PK.
To report a case of aberrant corneal nerve regeneration after myopic photorefractive keratectomy ... more To report a case of aberrant corneal nerve regeneration after myopic photorefractive keratectomy (PRK). One patient underwent bilateral PRK to correct a refractive error of -5.50 D in each eye. Thirteen months after the original PRK, the left eye underwent an uncomplicated PRK reoperation to correct a regression of -1.00 D. The central corneas were examined by confocal microscopy preoperatively in both eyes, at 1 and 2 years after the original PRK in the right eye, and before and 1 and 2 years after the PRK reoperation in the left eye. Aberrant anterior stromal nerves with a coiled course and irregular branching pattern were identified 22 micro m deep to the most anterior keratocyte layer at 1 year after the PRK reoperation in the left eye and remained unchanged 2 years after reoperation. No abnormal stromal nerves were identified in the left eye before the reoperation or at any time in the right eye. Aberrant regeneration of corneal stromal nerves may occur after myopic PRK reoperation.
Journal of Cataract and Refractive Surgery, Feb 1, 2004
To compare the measured ablation depth after myopic laser in situ keratomileusis (LASIK) and phot... more To compare the measured ablation depth after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) with the predicted ablation depth.
Purpose-To compare long-term keratometric changes after penetrating keratoplasty (PK) for keratoc... more Purpose-To compare long-term keratometric changes after penetrating keratoplasty (PK) for keratoconus and Fuchs' endothelial dystrophy. Design-Retrospective, comparative case series Methods-We retrospectively analyzed 168 corneas after PK for keratoconus (85 eyes of 63 subjects) and Fuchs' dystrophy (83 eyes of 60 subjects). Patients were examined after final suture removal at 12 months after PK to 30 years after surgery. Operations were performed by one surgeon using the same suturing technique in all cases. Eyes were excluded from further analysis after re-grafting or after relaxing incisions. Mean keratometric corneal power and astigmatism were measured by manual keratometry. Data were assessed by using generalized estimating equation models to determine change over time. Results-Mean keratometric corneal power and astigmatism increased through 30 years after PK for keratoconus (P<.001 and P<.001), but did not change through 20 years after PK for Fuchs dystrophy (P=.55 and P=.55) The change in keratometric corneal power and astigmatism after PK in keratoconus patients only differed from the change in Fuchs dystrophy patients 10 or more years after PK (P=.002 and P=.003).
The authors mention the use of a calibrated confocal microscope for the measurement of corneal th... more The authors mention the use of a calibrated confocal microscope for the measurement of corneal thickness and conclude that their results represent the true mean corneal thickness, a figure that was less than that measured with ultrasound pachymetry and Orbscan. They also argued that the calibration of ultrasonic pachymeters might not be accurate. However, even though the calibrated confocal microscope may have the exact measurement as the micrometer when measured on a contact lens, the same accuracy may not be transferable to in vivo examination of the human cornea. The authors mentioned that motion during the scan is a possible source of error. In contrast to their suggestion, however, the design of the confocal microscope may not help to minimize this error. The authors note that the cornea is somewhat stabilized by contact with the objective lens though a thin layer of methylcellose. It should be noted that this layer of methylcellose cannot stop anteriorposterior (A-P) movement of the eyeball or the patient's head during the examination. This can be demonstrated in the authors' own data, in which measurements of eight subjects (33.3%) had differences greater than 25-m between AP and posterior-anterior (PA) scan during the first measurement. It would be interesting if the authors compared the paired difference and used a Bland and Altman plot to assess the difference between the first and second measurements for both A-P and P-A scans. Results from repeating measurements of the same procedure is the way to assess the repeatability of equipment.
The corneal endothelium is derived from the neural crest. A general classification of disorders o... more The corneal endothelium is derived from the neural crest. A general classification of disorders of development of the neural crest has been previously presented (Johnston). Disorders of the corneal endothelium may be considered according to a modification of this scheme to reflect its true embryologic origin. In this classification, corneal endothelial disorders are catagorized as abnormalities of neural crest cell formation (cyclopia), migration (Peters' anomaly), proliferation (iridocorneal endothelial syndrome), final differentiation (Fuchs' dystrophy), and acquired abnormalities (metaplasia, abiatrophy, and proliferation).
Relationships of the masked gulls.-Although molecular biologists may have useful information for ... more Relationships of the masked gulls.-Although molecular biologists may have useful information for ornithologists, they usually overlook the possibility that ornithologists might also be able to tell them something. From work in the fi eld and with museum specimens, I know most of the smaller, more or less masked, southern gulls whose affi nities Given et al. (2005) analyzed, and I have some problems with their conclusion that these species are all related to each other and also to the northern Black-headed Gull (Larus ridibundus). First, Given et al. are not the fi rst to suggest that the Black-headed Gull has a southern relative. Murphy (1936:1084) wrote of the Brown-hooded Gull (L. maculipennis): This Patagonian gull is so closely related to the [Black-headed] Gull of Europe that Hellmayr (1932, 412) believes the relationship between the two might possibly be regarded as subspecifi c. Aplin (1894, 211) states, furthermore, that in voice and actions the Argentine bird is much like ridibundus, a fact that had also been noted by Darwin.
Background: Central corneal thickness greater than 0.520 mm causes true intraocular pressure to b... more Background: Central corneal thickness greater than 0.520 mm causes true intraocular pressure to be overestimated when the technique of applanation tonometry is used to measure intraocular pressure. Objective: To compare the corneal thickness measurements of patients enrolled in a study of ocular hypertension with those of age-matched control subjects with normal intraocular pressure. Methods: Central corneal pachymetry using an optical pachymeter was performed on each study subject (n=55) at baseline and in an independent sample of control subjects. A 2 sample, 2-tailed t test was used to compare the 2 populations. Results: The patients with ocular hypertension had significantly higher mean corneal thickness measurements (mean±SD, 0.594±0.037 mm) than the control group (0.563±0.027 mm) (PϽ.001). Conclusion: Corneal thickness may be a confounding factor in the measurement of intraocular pressure, and this may modify the risk for progression to glaucoma in patients with ocular hypertension.
Purpose-To compare subbasal nerve densities estimated from images recorded by the Tandem Scanning... more Purpose-To compare subbasal nerve densities estimated from images recorded by the Tandem Scanning and the ConfoScan 4 confocal microscopes. Methods-Confocal microscopy was used to estimate subbasal nerve density in 62 corneas of 40 subjects (18 corneas of 18 normal subjects and 44 corneas of 22 patients between 1 and 12 months after LASIK) At each examination, corneas were scanned first by using Tandem Scanning and then by using a ConfoScan 4 confocal microscope. Subbasal nerves from 2 to 4 scans per cornea were traced by using a semi-automated nerve analysis program. Nerve density was expressed as total nerve length divided by the sample area (µm/mm 2). Differences in nerve density between instruments were examined by using paired tests. Results-In normal corneas, subbasal nerve density was 10,658 ± 5,581 µm/mm 2 (mean ± SD) with the ConfoScan 4 and 5,534 ± 1,850 µm/mm 2 with the Tandem Scanning microscope (P<0.0001). One to 12 months after LASIK, mean subbasal nerve density was 2,477 ± 3,514 µm/mm 2 estimated with the ConfoScan 4 and 844 ± 983 µm/mm 2 estimated with the Tandem Scanning (P=0.0003). Estimates of nerve density were correlated between instruments (r=0.71, P<0.0001), although the mean difference between instruments was 2,308 ± 3,885 µm/mm 2 (P<0.0001). Conclusions-Mean subbasal nerve density estimated with the ConfoScan 4 was 2 to 3 times higher than density estimated with the Tandem Scanning confocal microscope. These differences must be considered when comparing subbasal nerve densities between studies that use different confocal microscopes.
Investigative Ophthalmology & Visual Science, May 1, 2005
ABSTRACT To determine changes in keratocyte density up to 3 years after LASIK. Prospective, nonra... more ABSTRACT To determine changes in keratocyte density up to 3 years after LASIK. Prospective, nonrandomized, comparative trial. Seventeen eyes of 11 patients received LASIK with a planned 180-microm flap to correct refractive errors between -2.0 diopters (D) and -11.0 D (mean, -6.56+/-2.44). Corneas were examined by using confocal microscopy before LASIK and 1, 3, 6, 12, 24, and 36 months after LASIK. Bright objects that resembled keratocyte nuclei were manually counted by a masked observer. Cell densities were determined in anterior and posterior halves of the stromal flap, anterior and posterior halves of the 100-microm-thick layer immediately behind the ablation (retroablation layer), and the posterior third of the stroma. The region of stroma that was ablated (as measured 1 month after LASIK) was omitted from preoperative analysis. Cell densities after LASIK were compared (using1-factor repeated-measures analysis of variance) with densities in the corresponding layer of the normal preoperative stroma (which served as its own control). Corneal keratocyte density. Before LASIK, keratocyte densities in the anterior and posterior stromal flap and the anterior retroablation layer were 34 818+/-5108 cells/mm(3) (mean +/- SD), 25 390+/-4045 cells/mm(3), and 21 328+/-2980 cells/mm(3), respectively, and densities in these layers decreased 14% to 20% at 1 month after LASIK (P&lt;0.001). Keratocyte densities in these layers remained stable at 3 and 6 months, and then gradually decreased further (P&lt;0.001) to 26% to 36% below pre-LASIK densities by 3 years. Keratocyte densities in the remaining stromal layers did not change after LASIK. Keratocyte densities in the stromal flap and in the anterior retroablation layer decrease during the first 6 months after LASIK and then decrease further during the next 2.5 years. Further studies on these patients and others are warranted to confirm these findings and learn their significance.
Salmonella tymphimurium enteritis; 0.36 Positive Periphlebitis, especially of vena miliary patter... more Salmonella tymphimurium enteritis; 0.36 Positive Periphlebitis, especially of vena miliary pattern on chest X-ray nasalis superior, both eyes 5, M, 13 Interstitial pneumonia Unknown Positive Periphlebitis of vena temporalis inferior, L.E. 6, M, 41 Bilateral parotitis; persistent 0.30 Positive Periphlebitis, both eyes pulmonary infiltrates 'Measured by an indirect immunofluorescence technique with monoclonal antibodies. 'Detected by an enzyme-linked immunosorbent assay using disrupted HTLV-1I1 as antigen in which antibody was considered to be detected if the absorbance ratio for the test serum compared to that of a standard negative serum was> 8.0
Purpose: To measure changes in keratocyte density up to 5 years after photorefractive keratectomy... more Purpose: To measure changes in keratocyte density up to 5 years after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Methods: This was a prospective, nonrandomized clinical trial. Eighteen eyes of 12 patients received PRK to correct a mean refractive error of -3.73 +/- 1.30 D, and 17 eyes of 11 patients received LASIK to correct a mean refractive error of -6.56 +/- 2.44 D. Corneas were examined by using confocal microscopy before and 6 months, 1 year, 2 years, 3 years, and 5 years after the procedures. Keratocyte densities were determined in five stromal layers in PRK patients and in six stromal layers in LASIK patients. Differences between preoperative and postoperative cell densities were compared by using Bonferroni-adjusted paired t tests. Results: After PRK, keratocyte density in the anterior stroma was decreased by 39%, 42%, 45%, and 47% at 6 months, 2 years, 3 years, and 5 years, respectively (P < .001). At 5 years, keratocyte density was decreased by 20% to 24% in the posterior stroma (P < .05). After LASIK, keratocyte density in the stromal flap was decreased by 22% at 6 months (P < .02) and 37% at 5 years (P < .005). Keratocyte density in the anterior retroablation zone was decreased 18% (P < .005) at 1 year and 43% (P < .005) at 5 years. At 5 years, keratocyte density was decreased by 19% to 22% (P < .05) in the posterior stroma. Conclusions: Keratocyte density is decreased in the anterior stroma after PRK and in the stromal flap and the retroablation zone after LASIK for up to 5 years. Posterior stromal keratocyte deficits are first noted at 5 years.
Purpose: To determine central keratocyte and subbasal nerve densities after penetrating keratopla... more Purpose: To determine central keratocyte and subbasal nerve densities after penetrating keratoplasty (PK) in clear grafts and in grafts with late endothelial failure (LEF). Methods: Ninety-nine clear grafts of 74 patients and 21 grafts with LEF in 19 patients were examined by confocal microscopy at 1 to 31 years after PK. Keratocyte density and number of keratocytes in a full-thickness column of stroma with frontal area of 1 mm(2) were determined from images. Subbasal nerve fiber bundle density was measured in the central cornea as the visible length of nerve per frame area. Comparisons were made to normal corneas. Results: Full-thickness keratocyte density in clear grafts (22,101 +/- 3,799 cells/mm(3), mean +/- SD, n = 99) was lower than in normal corneas (26,610 +/- 3,683 cells/mm(3), n = 63, P < .001) but did not differ from grafts with LEF (21,268 +/- 3,298 cells/mm(3), n = 12, P = .47). The number of keratocytes in clear grafts (10,325 +/- 1,708 cells, n = 99) was lower than in normal corneas (11,466 +/- 1,503 cells, n = 63, P < .001) but did not differ from grafts with LEF (10,778 +/- 1,760 cells, n=12, P = .39). Median subbasal nerve density in clear grafts (150 microm/mm(2), n = 94) was lower than in normal corneas (7,025 microm/mm(2), n = 76, P < .001), and nerve recovery correlated with time after PK (r = 0.36, P < .001, n = 94). Conclusions: Keratocyte density and number of keratocytes are decreased in penetrating grafts compared to normal corneas, but not compared to grafts with LEF. Subbasal nerve density does not recover to normal through 30 years after PK.
To report a case of aberrant corneal nerve regeneration after myopic photorefractive keratectomy ... more To report a case of aberrant corneal nerve regeneration after myopic photorefractive keratectomy (PRK). One patient underwent bilateral PRK to correct a refractive error of -5.50 D in each eye. Thirteen months after the original PRK, the left eye underwent an uncomplicated PRK reoperation to correct a regression of -1.00 D. The central corneas were examined by confocal microscopy preoperatively in both eyes, at 1 and 2 years after the original PRK in the right eye, and before and 1 and 2 years after the PRK reoperation in the left eye. Aberrant anterior stromal nerves with a coiled course and irregular branching pattern were identified 22 micro m deep to the most anterior keratocyte layer at 1 year after the PRK reoperation in the left eye and remained unchanged 2 years after reoperation. No abnormal stromal nerves were identified in the left eye before the reoperation or at any time in the right eye. Aberrant regeneration of corneal stromal nerves may occur after myopic PRK reoperation.
Journal of Cataract and Refractive Surgery, Feb 1, 2004
To compare the measured ablation depth after myopic laser in situ keratomileusis (LASIK) and phot... more To compare the measured ablation depth after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) with the predicted ablation depth.
Purpose-To compare long-term keratometric changes after penetrating keratoplasty (PK) for keratoc... more Purpose-To compare long-term keratometric changes after penetrating keratoplasty (PK) for keratoconus and Fuchs' endothelial dystrophy. Design-Retrospective, comparative case series Methods-We retrospectively analyzed 168 corneas after PK for keratoconus (85 eyes of 63 subjects) and Fuchs' dystrophy (83 eyes of 60 subjects). Patients were examined after final suture removal at 12 months after PK to 30 years after surgery. Operations were performed by one surgeon using the same suturing technique in all cases. Eyes were excluded from further analysis after re-grafting or after relaxing incisions. Mean keratometric corneal power and astigmatism were measured by manual keratometry. Data were assessed by using generalized estimating equation models to determine change over time. Results-Mean keratometric corneal power and astigmatism increased through 30 years after PK for keratoconus (P<.001 and P<.001), but did not change through 20 years after PK for Fuchs dystrophy (P=.55 and P=.55) The change in keratometric corneal power and astigmatism after PK in keratoconus patients only differed from the change in Fuchs dystrophy patients 10 or more years after PK (P=.002 and P=.003).
The authors mention the use of a calibrated confocal microscope for the measurement of corneal th... more The authors mention the use of a calibrated confocal microscope for the measurement of corneal thickness and conclude that their results represent the true mean corneal thickness, a figure that was less than that measured with ultrasound pachymetry and Orbscan. They also argued that the calibration of ultrasonic pachymeters might not be accurate. However, even though the calibrated confocal microscope may have the exact measurement as the micrometer when measured on a contact lens, the same accuracy may not be transferable to in vivo examination of the human cornea. The authors mentioned that motion during the scan is a possible source of error. In contrast to their suggestion, however, the design of the confocal microscope may not help to minimize this error. The authors note that the cornea is somewhat stabilized by contact with the objective lens though a thin layer of methylcellose. It should be noted that this layer of methylcellose cannot stop anteriorposterior (A-P) movement of the eyeball or the patient's head during the examination. This can be demonstrated in the authors' own data, in which measurements of eight subjects (33.3%) had differences greater than 25-m between AP and posterior-anterior (PA) scan during the first measurement. It would be interesting if the authors compared the paired difference and used a Bland and Altman plot to assess the difference between the first and second measurements for both A-P and P-A scans. Results from repeating measurements of the same procedure is the way to assess the repeatability of equipment.
The corneal endothelium is derived from the neural crest. A general classification of disorders o... more The corneal endothelium is derived from the neural crest. A general classification of disorders of development of the neural crest has been previously presented (Johnston). Disorders of the corneal endothelium may be considered according to a modification of this scheme to reflect its true embryologic origin. In this classification, corneal endothelial disorders are catagorized as abnormalities of neural crest cell formation (cyclopia), migration (Peters' anomaly), proliferation (iridocorneal endothelial syndrome), final differentiation (Fuchs' dystrophy), and acquired abnormalities (metaplasia, abiatrophy, and proliferation).
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Papers by William Bourne