Confocal microscopy of a patient with irregular astigmatism after LASIK reoperations and relaxation incisions

Comparison of modified corneal cross-linking with intrastromal voriconazole for the treatment of fungal corneal ulcer

The present study aimed to evaluate the efficacy of modified corneal cross-linking (CXL) for the treatment of fungal corneal ulcers compared with that following intrastromal voriconazole injection. In total, 31 patients with fungal corneal ulcers treated at The General Hospital of Northern Theater Command between October 2017 and October 2019 were enrolled. Among them, 10 eyes were treated with ultraviolet A (UV-A)/riboflavin CXL (CXL group), whilst 21 eyes were treated with debridement combined with intrastromal voriconazole (stromal injection group). Preoperative microbiological examination was performed in both groups, and evaluated using Fisher's exact test. Postoperatively, infection control and total efficacy rates, localized lesion, ulcer healing rate 1 week after surgery, visual acuity and complications were evaluated using Fisher's exact test, however visual acuity was analyzed by mixed-model ANOVA. The results showed that the pre-operative species distribution between the CXL and stromal injection groups did not significantly differ. The infection control rate in the CXL group was notably higher compared with that in the stromal injection group (P=0.04). Furthermore, the total efficacy rate in the CXL group was also markedly higher compared with that in the stromal injection group, though no statistically significant differences were observed. Localized lesions were observed in nine eyes (90.0%) in the CXL group and nine eyes (42.9%) in the stromal injection group (P=0.02). However, the rate of ulcer healing at 1 week postoperatively and the logarithm of the minimum angle of resolution (logMAR) of visual acuity were not found to be significantly different between the two groups. In terms of complications, with the exception of one patient in the CXL group exhibiting loss of corneal transparency and one patient in the stromal injection group presenting with partial corneal thinning, no other forms of complications were observed. In conclusion, the present study suggested that CXL could have a beneficial impact for treating fungal corneal ulcers in the aspects of infection control, localized lesions and accelerated epithelialization. In addition, except the loss of corneal transparency, this treatment approach could be applied with reduced risks of adverse events.

Four-dimensional multiphoton confocal microscopy: the new frontier in cellular imaging

This paper reviews new developments in microscopy that combine gene transfer technology, multiphoton confocal fluorescence microscopy, live cell imaging and digital imaging techniques that provide unique insights into the complex physiological processes involved in tissue function at the cellular and subcellular level. The evolution of this novel, new technology is discussed with particular attention to earlier achievements in noninvasive ocular surface imaging. The practical basis of confocal microscopy, multiphoton confocal fluorescence microscopy, and the vital fluorescent labeling of cells in living tissues are also discussed. Additionally, one application using retroviral gene transfer to express enhanced green fluorescent protein in living wound healing fibroblasts is presented as an example of how living biology can be studied in situ in four dimensions (x, y, z, time).

Clinical corneal confocal microscopy

Confocal microscopy allows non-invasive in vivo imaging of the ocular surface. Its unique physical properties enable microscopic examination of all layers of the cornea and have been used to investigate numerous corneal diseases: epithelial changes, numerous stromal degenerative or dystrophic diseases, endothelial pathologies, corneal deposits, infections, and traumatic lesions. It offers a new approach to study the physiological reactions of the cornea to different stimuli and the pathophysiologic events leading to corneal dysfunction in certain diseases. Confocal microscopy proves to be a powerful diagnostic tool and is especially of value in certain corneal diseases by allowing straightforward and non-invasive recognition of the pathologic conditions.

In vivo three-dimensional confocal laser scanning microscopy of the epithelial nerve structure in the human cornea

PURPOSE

Evaluation of a new method for in vivo visualization of the distribution and morphology of human anterior corneal nerves.

METHOD

The anterior cornea was examined to a depth of 100 microm in four human volunteers with a confocal laser scanning microscope (CLSM) using a Rostock Cornea Module (developed in house) attached to a Heidelberg Retina Tomograph II (Heidelberg Engineering, Germany). Optical sections were digitally reconstructed in 3D using AMIRA (TGS Inc., USA). The scanned volumes had a greatest size of 300 x 300 x 40 microm and voxel size of 0.78 x 0.78 x 0.95 microm.

RESULTS

The spatial arrangement of the epithelium, nerves and keratocytes was visualized by in vivo 3D-CLSM. The 3D-reconstruction of the volunteers' corneas in combination with the oblique sections gave a picture of the nerves in the central human cornea. Thin nerves run in the subepithelial plexus aligned parallel to Bowman's layer and are partially interconnected. The diameter of these fibres varied between 1.0 and 5 microm. Thick fibres rose out of the deeper stroma. The diameter of the main nerve trunks was 12+/-2 microm. Branches penetrating the anterior epithelial cell layer could not be visualized.

CONCLUSIONS

3D-CLSM allows analysis of the spatial arrangement of the anterior corneal nerves and visualization of the epithelium and keratocytes in the living human cornea. The developed method provides a basis for further studies of alterations of the cellular arrangement and epithelial innervation in corneal disease. This may help to clarify alterations of nerve fibre patterns under various clinical and experimental conditions.

Pathologic findings in postmortem corneas after successful laser in situ keratomileusis

PURPOSE

To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK).

METHODS

Corneas from 48 eyes of 25 postmortem patients were processed for histology and transmission electron microscopy (TEM). The 25 patients had LASIK between 3 months and 7 years prior to death. Evaluation of all 5 layers of the cornea and the LASIK flap interface region was done using routine histology, periodic acid-Schiff (PAS)-stained specimens, toluidine blue-stained thick sections, and TEM.

RESULTS

In patients for whom visual acuity was known, the first postoperative day uncorrected visual acuity was 20/15 to 20/30. In patients for whom clinical records were available, the postoperative corneal topography was normal and clinical examination showed a semicircular ring of haze at the wound margin of the LASIK flap. Histologically, the LASIK flap measured, on average, 142.7 microm (range, 100-200). A spectrum of abnormal histopathologic and ultrastructural findings was present in all corneas. Findings at the flap surface included elongated basal epithelial cells, epithelial hyperplasia, thickening and undulations of the epithelial basement membrane (EBM), and undulations of Bowman's layer. Findings in or adjacent to the wound included collagen lamellar disarray; activated keratocytes; quiescent keratocytes with small vacuoles; epithelial ingrowth; eosinophilic deposits; PAS-positive, electron-dense granular material interspersed with randomly ordered collagen fibrils; increased spacing between collagen fibrils; and widely spaced banded collagen. There was no observable correlation between postoperative intervals and the severity or type of pathologic change except for the accumulation the electron-dense granular material.

CONCLUSIONS

Permanent pathologic changes were present in all post-LASIK corneas. These changes were most prevalent in the lamellar interface wound. These changes along with other pathologic alterations in post-LASIK corneas may change the functionality of the cornea after LASIK.

Late traumatic dislocation of laser in situ keratomileusis flaps

We present 2 patients with late traumatic laser in situ keratomileusis flap dislocation 8 months and 17 months after surgery. One patient had a sharp trauma that caused a partial laceration and the second patient had a blunt trauma that caused a dislocation of the flap. The corneas were examined with slitlamp microscopy, computed corneal topography, and confocal microscopy. One flap was repositioned surgically; the other was treated conservatively with an eye patch. The final visual outcomes were good and illustrate the benefit of immediate attention and flap repositioning.

In vivo confocal microscopy of the human cornea

AIMS

To describe the optics of in vivo confocal microscopy, its advantages over previous methods, and to summarise the literature that arose from its use for the observation of the human cornea. A critical review of the clinical usefulness of this new technology for the corneal examination is undertaken.

METHODS

Confocal microscopes obtain increased resolution by limiting the illumination and observation systems to a single point. Rapid scanning is used to reconstruct a full field of view and allows for "real time" viewing.

RESULTS

Coronal sections of the in situ epithelium, Bowman's membrane, stroma, and endothelium can be visualised at a resolution of 1-2 micro m. A backscattered light intensity curve allows objective measurements of sublayer thickness and corneal haze to be taken. In vivo confocal microscopy is therefore particularly useful in the areas of infective keratitis, corneal dystrophies, refractive surgery, and contact lens wear, where it aids in differential diagnosis and detection of subtle short and long term changes. Real time endothelial cell assessment can also be performed.

CONCLUSION

Because of their ability to visualise living tissue at cellular levels, confocal microscopes have proved useful additions to the current clinical tools.

Mismatch between flap and stromal areas after laser in situ keratomileusis as source of flap striae

PURPOSE

To calculate theoretically the magnitude of the excess area between the lower surface of the flap and the underlying ablated stroma.

METHODS

On the initial assumptions of a nonextensible flap and a spherical cornea, flap and ablated stromal areas were determined as a function of myopic correction in the range of 0 to -12 diopters (D) for typical values of corneal radius (7.8 mm) and flap thickness (160 microm), together with a range of ablation zone diameters (4.0 mm, 6.0 mm, 8.0 mm, and 10.0 mm).

RESULTS

Excess flap area increases with the magnitude of the refractive correction and the diameter of the ablated zone. For a -6.0 D correction and an 8.0 mm ablation zone, the excess area is nominally about 1.0 mm(2), giving a potential overlap of the flap at the edge opposite the hinge of about 100 microm. CONCLUSIONS; Excess flap area may cause striae because of wrinkling. Although a nonextensible flap is assumed in the model, any stretching or contraction due to cutting the flap will be independent of the refractive correction. Hence, a mismatch in areas must still occur. This geometric effect may have clinical consequences in optical aberration, refractive regression, or impaired wound healing.

A prototype two-detector confocal microscope for in vivo corneal imaging

Confocal microscopy through-focusing (CMTF) of the cornea produces a three-dimensional (3-D) display of corneal structure and intensity profiles that allow objective measurements of corneal sublayer thickness and relative assessment backscattering of light. In this study, a prototype confocal instrument was evaluated in which a photon counting photomultiplier tube (PMT) detector was added to provide faster and more quantitative measurements, while still maintaining the imaging capability of the microscope. To acquire images and measure backscattered light simultaneously, an uncoated pellicle beam splitter was incorporated into the light path of the confocal microscope. This beam splitter reflects 8% of the confocal signal to the PMT. The CMTF scans were performed on four rabbits using the prototype instrument. Corneal images and 3-D reconstructions acquired with and without the beam splitter in the light path appeared identical. Both the camera and PMT CMTF curves had easily identifiable peaks corresponding to the epithelium, basal lamina, and endothelium. No significant differences were found between PMT and camera CMTF measurements of epithelial, stromal, or corneal thickness (n = 12 scans). Furthermore, a high correlation was found between camera and PMT measurements (linear regression analysis, y = 0.999 x -0.4, r = 0.99, p < 0.001). The data suggest that by adding a pellicle beam splitter, CMTF intensity data can be acquired using a PMT. The PMT has a faster sampling rate and greater dynamic range than the camera and provides a count of the photons detected. Thus, the instrument has the potential for improving corneal pachymetry and back-scattering measurements while still providing high-resolution corneal images.

In vivo confocal microscopy through-focusing to measure corneal flap thickness after laser in situ keratomileusis

PURPOSE

To measure flap thickness in laser in situ keratomileusis (LASIK) patients using in vivo confocal microscopy through-focusing (CMTF) and compare measured versus intended flap thickness achieved by 2 microkeratomes, the Automated Corneal Shaper(R) (ACS) (Chiron Bausch & Lomb) and the Hansatome (Bausch & Lomb).

SETTING

Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA.

METHODS

Twenty-seven eyes of 27 patients were examined by in vivo CMTF 3 to 12 months after LASIK was performed with the ACS (12 patients) or Hansatome (15 patients) microkeratome. The central cornea was scanned, and the epithelium, flap, stroma, and total corneal thickness were measured. Normalized flap thickness (NFT) was also calculated to account for changes in epithelial thickness that may have occurred postoperatively.

RESULTS

The mean posterior stromal thickness was 341.1 microm +/- 53.9 (SD) (range 233 to 431 microm) in the ACS group and 320.3 +/- 42.3 microm (range 258 to 382 microm) in the Hansatome group. The mean nonnormalized flap thickness was 132.7 +/- 12.5 microm (range 11 to 151 microm) in the ACS group and 167.4 +/- 21.4 microm (range 141 to 209 microm) in the Hansatome group. The NFT was 129.6 +/- 9.5 microm and 158.4 +/- 22.1 microm, respectively. Both microkeratomes cut significantly less than intended (P <.05); however, the ACS cut a thinner-than-intended thickness in all cases, and the Hansatome cut thicker than intended in 13% of cases. The Hansatome also showed significantly greater variability in flap thickness than the ACS (P <.05).

CONCLUSIONS

A significant difference in precision was noted between the 2 microkeratomes. The findings emphasize the importance of performing thickness measurements and the usefulness of in vivo CMTF in making these determinations to ensure the safety and effectiveness of LASIK.

Evaluation of corneal stromal changes in vivo after laser in situ keratomileusis with confocal microscopy

PURPOSE

To assess by in vivo confocal microscopy the modifications of the corneal stroma after laser in situ keratomileusis (LASIK) for myopia.

DESIGN

Nonrandomized comparative (self-controlled) trial.

PARTICIPANTS

Sixteen eyes of 13 patients were examined before surgery and at days 8, 30, and 90, and 9 eyes were examined at 6 months postoperatively using an in vivo confocal microscope. TESTING/INTERVENTION: Stromal morphologic changes, keratocyte density, flap thickness, and subclinical haze were evaluated and compared at different time points. LASIK was performed with a Flapmaker microkeratome (Solan Ophthalmic products, Jacksonville, FL) and a Lasersight LSX excimer laser (LaserSight Technologies Inc., Winter Park, FL).

MAIN OUTCOME MEASURE

Confocal microscopy results.

RESULTS

Microfolds at the Bowman's layer were found in most eyes, as well as variable reflectivity particles (pa) located at the interface level in all eyes examined postoperatively. The density of these particles significantly decreased with time with, respectively, 504 +/- 101 pa/mm2 at day 8 and 380 +/- 111 pa/mm2 at day 30 (P = 0.003), 332 +/- 100 pa/mm2 at month 3 and 312 +/- 40 pa/mm2 at month 6. The mean flap and the activated-cells area thicknesses were, respectively, 102 +/- 26 microm and 61 +/- 19 microm and showed significant negative correlation (P < 0.0001). The intensity of the added peak (47.3 microm 8.6%), corresponding to the subclinical haze, realized by Z-scan measure, was also negatively correlated with flap thickness (P = 0.01). Keratocyte (k) density quantified in the posterior stroma significantly increased from day 0 (480 +/- 67 k/mm2) to day 8 (701 +/- 41 k/mm2, P < 0.0001 compared with day 0) and day 30 (917 +/- 143 k/mm2, P = 0.0006, compared with day 0) but significantly decreased at 3 months postoperatively (597 +/- 56 k/mm2, P < 0.0001 compared with day 30) to reach the initial level at month 6 (502 +/- 41 k/mm2, nonsignificant compared with day 0). There was no correlation between preoperative or postoperative spherical equivalent and the density of particles, keratocytes, and the haze intensity.

CONCLUSIONS

This study confirms the presence of microfolds and particles at the interface level, as well as subclinical impairment. Evaluation of keratocyte density constitutes a major contribution of confocal microscopy toward an understanding of the keratocyte response to corneal wound healing after corneal refractive surgery. Moreover, flap thickness seems to be involved in the postoperative cellular activation with a higher response when thin.

In vivo confocal microscopy of corneal epithelial ingrowth through a laser in situ keratomileusis flap buttonhole

We report a case of epithelial ingrowth through a buttonhole 6 months after laser in situ keratomileusis. Elevation topography showed irregular astigmatism and an unreliable pachymetric map. In vivo confocal microscopy showed an epithelial basal cell mosaic with prominent borders and distinct nuclei. No corneal nerves were identified in any image. Cells in the anterior stroma possessed bright, reflective nuclei and appeared to form clusters. The interface between the stromal bed and the flap had formation of nests of fibrotic tissue and epithelial cells.