Automated assessment of keratocyte density in clinical confocal microscopy of the corneal stroma

A Review On digital image processing techniques for in-Vivo confocal images of the cornea

This work reviews the scientific literature regarding digital image processing for in vivo confocal microscopy images of the cornea. We present and discuss a selection of prominent techniques designed for semi- and automatic analysis of four areas of the cornea (epithelium, sub-basal nerve plexus, stroma and endothelium). The main context is image enhancement, detection of structures of interest, and quantification of clinical information. We have found that the preprocessing stage lacks of quantitative studies regarding the quality of the enhanced image, or its effects in subsequent steps of the image processing. Threshold values are widely used in the reviewed methods, although generally, they are selected empirically and manually. The image processing results are evaluated in many cases through comparison with gold standards not widely accepted. It is necessary to standardize values to be quantified in terms of sensitivity and specificity of methods. Most of the reviewed studies do not show an estimation of the computational cost of the image processing. We conclude that reliable, automatic, computer-assisted image analysis of the cornea is still an open issue, constituting an interesting and worthwhile area of research.

Corneal confocal microscopy identifies a reduction in corneal keratocyte density and sub-basal nerves in children with type 1 diabetes mellitus

PURPOSE

To assess whether alterations in stromal keratocyte density are related to loss of corneal nerve fibres in children with type 1 diabetes mellitus (T1DM).

METHODS

Twenty participants with T1DM and 20 age-matched healthy controls underwent corneal confocal microscopy. Corneal sub-basal nerve morphology and corneal keratocyte density (KD) were quantified.

RESULTS

Corneal nerve fibre density (CNFD) (p<0.001), corneal nerve branch density (p<0.001), corneal nerve fibre length (CNFL) (p<0.001) and inferior whorl length (IWL) (p<0.001) were lower in children with T1DM compared with healthy controls. Anterior (p<0.03) and mid (p=0.03) stromal KDs were lower with no difference in posterior KD (PKD) in children with T1DM compared with controls. Age, duration of diabetes, height, weight and body mass index did not correlate with anterior (AKD), mid (MKD) or PKD. Inverse correlations were found between glycated haemoglobin and PKD (r=-0.539, p=0.026), bilirubin with MKD (r=-0.540, p=0.025) and PKD (r=-0.531, p=0.028) and 25-hydroxycholecalciferol with MKD (r=-0.583, p=0.018). CNFD, CNFL and IWL did not correlate with AKD, MKD or PKD.

CONCLUSION

This study demonstrates a reduction in corneal nerves and anterior and mid stromal KD in children with T1DM, but no correlation between corneal nerve and keratocyte cell loss.

[Morphological changes of cornea in children with hyperopia in the immediate and remote postoperative period after laser keratomieleusis according to confocal microscopy data]

Studying morphological changes of cornea in the remote postoperative period is becoming increasingly relevant with refractive surgeries being adapted for children.

PURPOSE

comparative analysis of keratocyte density and hystomorphologic changes of cornea after laser in situ keratomieleusis (LASIK) and femtosecond laser-assisted LASIK (FS-LASIK) in children with hyperopia.

MATERIAL AND METHODS

109 patients aged 6-17 years in 2 groups were examined with 'Confoscan-4' confocal microscope.

RESULTS

In comparison with initial data, keratocyte density decreased in the immediate postoperative period after FS-LASIK and LASIK in average by 17.09%, 64.31% and 12.2% in the corneal flap, directly in the laser influence zone (interface) and in the retroablation zone respectively. After 5 years, keratocyte density decreased in the corneal flap, interface zone and retroablation zone by 12.01%, 48.71% and 8.06% respectively in comparison with initial data. A circular scar at the flap edge was left after FS-LASIK; keratocyte density in the corneal flap and in the interface zone was in average 8.9% and 15.28% higher respectively, and twice more subepithelial nerves were noted compared to LASIK.

CONCLUSIONS

In the remote postoperative period keratocyte density in the corneal decreased in average by 43% after FS-LASIK and by 46% after LASIK in comparison with initial data. No changes were seen in the morphologic state of the cornea outside the influence zone. Both the technologies are safe, however keratocyte density and the number of subepithelial nerves are higher in the cornea flap and in the interface zone after FS-LASIK; corneal stability is assured by a circular scar formed at the flap edge.

Changes in Keratocyte Density and Visual Function Five Years After Laser In Situ Keratomileusis: Femtosecond Laser Versus Mechanical Microkeratome

PURPOSE

To determine the effects of keratocyte loss on optical properties and vision after laser in situ keratomileusis (LASIK) with the flap created with a femtosecond laser or a mechanical microkeratome.

DESIGN

Randomized clinical paired-eye study.

METHODS

Both eyes of 21 patients received LASIK for myopia or myopic astigmatism. One eye of each patient was randomized by ocular dominance to flap creation with a femtosecond laser and the other eye to flap creation with a mechanical microkeratome. Before LASIK and at 1, 3, and 6 months and 1, 3, and 5 years after LASIK, keratocyte density was measured using confocal microscopy, and high-contrast visual acuity and anterior corneal wavefront aberrations were measured by standard methods. At each visit, all variables were compared between methods of creating the flap and to the same variable before treatment using paired tests with Bonferroni correction for multiple comparisons.

RESULTS

Keratocyte density in the flap decreased by 20% during the first year after LASIK and remained low through 5 years (P < .001). High-order wavefront aberrations increased and uncorrected visual acuity improved immediately after surgery, but these variables did not change further to 5 years. There were no differences in any variables between treatments.

CONCLUSIONS

A sustained reduction in keratocyte density does not affect vision or optical properties of the cornea through 5 years after LASIK. The method of creating a LASIK flap does not influence the changes in keratocyte density in the flap.

Keratocyte density 3 months, 15 months, and 3 years after corneal surface ablation with mitomycin C

PURPOSE

To study the effects of surface ablation with mitomycin C (MMC) on keratocyte population.

DESIGN

Prospective, nonrandomized, interventional, comparative case series.

METHODS

Thirty two eyes treated with surface ablation with 0.02% MMC were compared with nontreated eyes at Vissum Santa Hortensia, Madrid, Spain. Keratocyte density was measured with the Heidelberg Retina Tomograph II (Rostock Cornea Module) 3, 15, and 36 to 42 months after the surgery in the anterior, mid, and posterior stroma, and compared with control eyes.

RESULTS

Three months postoperatively, we found a lower stromal bed density compared to controls (16 993 ± 8001 vs 29 660 ± 5904 cells/mm(3), P = .0001), while there was a significantly higher cell density in the mid (30 783 ± 9300 vs 18 505 ± 1996 cells/mm(3), P = .0001) and deep stroma (30 268 ± 8321 vs 18 438 ± 2139 cells/mm(3), P = .0001). Three years after the surgery, the cellularity in the stromal bed had not significantly changed from the 3-month follow-up, but the density in the mid (18 889 ± 3474 cells/mm(3)) and posterior stroma (18 992 ± 3402 cells/mm(3)) had decreased to show no difference from controls. The mean cell density between the anterior, mid, and posterior stroma was not significantly different from controls 15 months and 3 years after the surgery.

CONCLUSION

Our study suggests that there is a reorganization of the stromal cell population soon after surface ablation with MMC, with a decrease in the stromal bed compensated initially with an increase in the mid and posterior stroma. Corneal cellularity tends to normalize over time, and 3 years postoperatively the mean cell density throughout the cornea seems to maintain normal values.

Automated detection and cell density assessment of keratocytes in the human corneal stroma from ultrahigh resolution optical coherence tomograms

Keratocytes are fibroblast-like cells that maintain the optical clarity and the overall health of the cornea. The ability to measure precisely their density and spatial distribution in the cornea is important for the understanding of corneal healing processes and the diagnostics of some corneal disorders. A novel computerized approach to detection and counting of keratocyte cells from ultra high resolution optical coherence tomography (UHR-OCT) images of the human corneal stroma is presented. The corneal OCT data is first processed using a state-of-the-art despeckling algorithm to reduce the effect of speckle on detection accuracy. A thresholding strategy is then employed to allow for improved delineation of keratocyte cells by suppressing similarly shaped features in the data, followed by a second-order moment analysis to identify potential cell nuclei candidates. Finally, a local extrema strategy is used to refine the candidates to determine the locations and the number of keratocyte cells. Cell density distribution analysis was carried in 3D UHR-OCT images of the human corneal stroma, acquired in-vivo. The cell density results obtained using the proposed novel approach correlate well with previous work on computerized keratocyte cell counting from confocal microscopy images of human cornea.

Anterior keratocyte depletion in fuchs endothelial dystrophy

OBJECTIVE

To determine if keratocyte populations are different in corneas with Fuchs dystrophy compared with control corneas.

METHODS

Eleven corneas excised during penetrating keratoplasty for Fuchs dystrophy and 5 control corneas of eyes enucleated for choroidal melanoma were examined using light microscopy. Twenty control corneas age-matched to the corneas with Fuchs dystrophy were examined using confocal microscopy in vivo. The number of keratocytes in a full-thickness column of central stroma with frontal area of 1 mm(2), determined using histologic and confocal methods, was compared between corneas with Fuchs dystrophy and controls.

RESULTS

By histology, the mean (SD) number of cells in a full-thickness column of stroma in Fuchs dystrophy (12 215 [1394] cells) was less than in control corneas (15 628 [710] cells; P < .001). The mean (SD) number of keratocytes in the anterior 10% of the stroma of corneas with Fuchs dystrophy (682 [274] cells) was less than in the control corneas measured using histology (1858 [404] cells; P < .001) and confocal microscopy (1481 [397] cells; P < .001).

CONCLUSIONS

Keratocytes are depleted by 54% to 63% in the anterior 10% of the stroma of corneas that require penetrating keratoplasty for Fuchs dystrophy. Keratocyte loss might contribute to anterior stromal changes that persist and degrade vision after endothelial keratoplasty.

Keratocyte density after laser-assisted subepithelial keratectomy with mitomycin C

PURPOSE

To study the effects of laser-assisted subepithelial keratectomy (LASEK) with mitomycin C (MMC) on the keratocyte population.

DESIGN

Prospective, nonrandomized, interventional, comparative case series.

METHODS

Fifty-six eyes treated at Vissum Santa Hortensia, Madrid, Spain, were included in the study. We compared 28 eyes treated with LASEK with intraoperative 0.02% MMC versus 28 non-treated eyes. Keratocyte density was measured 3 months after the surgery in the anterior, mid, and posterior stroma and was compared with the corresponding layers in the control eyes. The anterior layer in the LASEK group was compared with 2 layers in the control group: the most anterior stromal layer and the 80 μm-deep layer, because that was the mean ablation depth performed in eyes that underwent LASEK.

RESULTS

We found a statistically significantly lower keratocyte population in the most anterior stromal layer after LASEK with MMC compared with both the most anterior stromal layer and the 80 μm-deep layer in controls. On the contrary, the treated group showed a significantly higher keratocyte density in both the mid stroma and the deep stroma. The comparison between the average densities through the entire cornea showed a significantly higher keratocyte population in the LASEK with MMC group.

CONCLUSIONS

LASEK with MMC seems to cause a decrease in the anterior stromal cells 3 months after the surgery compared with nonoperated corneas. There seems to be a compensating proliferation of keratocytes in the deeper corneal layers, suggesting that the ability of keratocytes to repopulate the cornea is maintained after the surgical procedure.

Confocal microscopy of corneal stroma and endothelium after LASIK and PRK

PURPOSE

To compare with confocal microscopy the changes in stromal keratocyte density and endothelial cell count due to photorefractive keratectomy (PRK) and LASIK.

METHODS

In this prospective study, 32 eyes (16 myopic patients) were examined with the NIDEK Confoscan 3 confocal microscope before and 6 months after PRK and LASIK. The preoperative mean myopia was -2.85+/-0.99 diopters (D) (range: -1.00 to -4.00 D) in 24 eyes that underwent PRK and -2.94+/-0.96 D (range: -2.00 to -4.25 D) in 8 eyes that underwent LASIK. Keratocyte density in the anterior and posterior stroma and the endothelial cell count were measured. Statistically significant changes were assessed using the t test. P<.05 was considered statistically significant.

RESULTS

Preoperative hexagonal cell percentage in the LASIK group was 52.17+/-11.43 and 51.33+/-10.98 in the PRK group. Postoperatively, the percentages were 52.96+/-7.55 and 53.34+/-10.2, respectively. Six months postoperatively, keratocyte density changed by 367.12+/-103.35 cells/mm(2) (34.7% reduction) in the anterior stroma (P<.05) and 9.25+/-28.28 cells/mm(2) (1.31% reduction) in the posterior stroma (P>.05) for the LASIK group. In the PRK group, these values were 319.71+/-83.45 cells/mm(2) (31.13% reduction) in the anterior stroma (P<.05) and 0.17+/-38.97 cells/mm(2) (0.02% reduction) in the posterior stroma (P>.05). The changes in keratocyte densities were not statistically significant between groups (P>.05). The mean number of keratocytes decreased by 37.2% in the retroablation zone of the LASIK group (P<.05). No changes were noted in endothelial cell counts.

CONCLUSIONS

A significant decrease occurred in the number of stromal keratocytes in the anterior stroma. Despite differences in surgery, the change in keratocyte density and endothelial cell counts were similar between LASIK and PRK groups (P>.05).

Automated assessment of keratocyte density in stromal images from the ConfoScan 4 confocal microscope

Purpose. To develop a program to determine cell densities in images from the ConfoScan 4 (Nidek, Inc., Freemont, CA) confocal microscope and compare the densities with those determined in images obtained by the Tandem Scanning confocal microscope (Tandem Scanning Corp., Reston, VA). Methods. A program was developed that used image-processing routines to identify stromal cell nuclei in images from the ConfoScan 4 confocal microscope. Cell selection parameters were set to match cell densities from the program with those determined manually in 15 normal corneas of 15 volunteers. The program was tested on scans from 16 other normal volunteers and 17 volunteers 3 years after LASIK. Cell densities were compared to densities determined by manual assessment and to those in scans by the Tandem Scanning confocal microscope in the same corneas. Results. The difference in cell density between the automatic and manual assessment was -539 +/- 3005 cells/mm(3) (mean +/- SD, P = 0.11) in the 16 test corneas. Densities estimated from the ConfoScan 4 agreed with those from the Tandem Scanning confocal microscope in all regions of the stroma except in the anterior 10%, where the ConfoScan 4 indicated a 30% lower density. Conclusions. Differences in anterior stromal cell density between the ConfoScan 4 and the Tandem Scanning confocal microscope can be explained by the different optical designs. The lower spatial resolution of the ConfoScan 4 limits its ability to resolve thin layers. The adaptation of our earlier cell-counting program to the ConfoScan 4 provides a timesaving, objective, and reproducible means of determining stromal cell densities in images from the ConfoScan 4.

The effect of corneal light scatter on vision after penetrating keratoplasty

PURPOSE

To determine the effect of corneal light scatter on vision after penetrating keratoplasty (PK).

DESIGN

Cross-sectional study.

METHODS

setting: Cornea service at Mayo Clinic, Rochester, Minnesota. study population: Sixty-one eyes with clear grafts at 14.6 +/- 10.5 years after PK; 12 eyes with late endothelial failure (LEF) at 19.7 +/- 6.4 years after PK; 41 normal eyes. observation procedures: PK. main outcome measures: Backscatter from different depths of the cornea was measured by a custom scatterometer; intraocular forward light scatter was measured with a stray light meter; high-contrast visual acuity (HCVA) was measured by Early Treatment Diabetic Retinopathy Study (ETDRS) or Snellen chart; mesopic and photopic low-contrast visual acuity (LCVA) were measured with a 10% contrast chart.

RESULTS

Backscatter from the anterior, middle (stroma), and posterior thirds of the cornea was higher in clear grafts compared with normal (P < .001), and higher in grafts with LEF compared with clear grafts (P < .001). Corneal stromal backscatter from clear grafts correlated with time after keratoplasty (r = 0.21; P = .006; n = 61). Forward light scatter was higher in eyes with clear grafts compared with normal (P < or = .006), and higher in eyes with LEF compared with clear grafts (P < or = .01). Corneal stromal backscatter from clear grafts correlated with HCVA (r = 0.34; P = .02; n = 52), mesopic LCVA (r = 0.36; P = .01; n = 28), and photopic LCVA (r = 0.57; P < .001; n = 28). Forward scatter in eyes with clear grafts correlated with photopic LCVA (r = 0.38; P = .04; n = 26).

CONCLUSIONS

Light scattered from the cornea increases with time after PK and is associated with decreased high- and low-contrast vision.

Keratocyte and subbasal nerve density after penetrating keratoplasty

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.