W. Craig Fowler

A new paradigm for corneal wound healing research: The white leghorn chicken (Gallus gallus domesticus)

Purpose. To evaluate the chicken cornea as a model for corneal wound healing research. Methods. We conducted studies on normal chicken corneas and on corneas following mechanical debridement and photorefractive keratectomy (PRK). Results. The chicken cornea possesses six distinct layers that resemble the layers of the human cornea, including a substantial Bowman’s layer measuring 5.2 ± 0.3µm thick. Reepithelialization time was 44.8 ± 1.1 hours with a sliding rate of 75.3 ± 3.2µm/hour following mechanical debridement and 54.4 ± 2.8 hours with a sliding rate of 63.3 ± 3.2µm/hour for PRK-treated corneas. Biomicroscopic haze post-PRK peaked at 4–6 weeks and regressed until 20 weeks post-PRK. Histologic and clinical observations of wound healing strongly paralleled that noted in humans. Conclusion. The chicken cornea’s morphology and wound healing response render it a useful model for corneal wound healing investigations.

Mycobacterium chelonae canaliculitis associated with SmartPlug use.

Mycobacterium chelonae is ubiquitous in the environment but is an uncommon cause of ocular and periocular infections. It is a pathogen that has been gaining increased attention in the ophthalmic literature because of the relatively large number of infections associated with laser-assisted in situ keratomileusis and other forms of refractive surgery. The authors present 3 patients who developed canaliculitis culture positive for M. chelonae more than a year after SmartPlug placement. These cases highlight some of the clinical scenarios that may be encountered in those who present with canaliculitis with a history of intracanalicular plug placement. Therapeutic considerations are also suggested.

The free electron laser: a system capable of determining the gold standard in laser vision correction

Abstract Introduction. In laser vision correction surgery, lasers are generally utilized based on their beam-tissue interactions and corneal absorption characteristics. Therefore, the free electron laser, with its ability to provide broad wavelength tunability, is a unique research tool for investigating wavelengths of possible corneal ablation. Methods. Mark III free electron laser wavelengths between 2.94 and 6.7 μm were delivered in serial 0.1 μm intervals to corneas of freshly enucleated porcine globes. Collateral damage, ablation depth, and ablation diameter were measured in histologic sections. Results. The least collateral damage (12–13 μm) was demonstrated at three wavelengths: 6.0, 6.1 (amide I), and 6.3 μm. Minimal collateral damage (15 μm) was noted at 2.94 μm (OH-stretch) and at 6.2 μm. Slightly greater collateral damage was noted at 6.45 μm (amide II), as well as at the 5.5–5.7 μm range, but this was still substantially less than the collateral damage noted at the other wavelengths tested. Conclusions. Our results suggest that select mid-infrared wavelengths have potential for keratorefractive surgery and warrant additional study. Further, the free electron lasers ability to allow parameter adjustment in the far-ultraviolet spectrum may provide unprecedented insights toward establishing the gold-standard parameters for laser vision correction surgery.

Electron tomography of fiber cell cytoplasm and dense cores of multilamellar bodies from human age-related nuclear cataracts.

Human nuclear cataract formation is a multi-factorial disease with contributions to light scattering from many cellular sources that change their scattering properties over decades. The aging process produces aggregation of cytoplasmic crystallin proteins, which alters the protein packing and texture of the cytoplasm. Previous studies of the cytoplasmic texture quantified increases in density fluctuations in protein packing and theoretically predicted the corresponding scattering. Multilamellar bodies (MLBs) are large particles with a core of crystallin cytoplasm that have been suggested to be major sources of scattering in human nuclei. The core has been shown to condense over time such that the refractive index increases compared to the adjacent aged and textured cytoplasm. Electron tomography is used here to visualize the 3D arrangement of protein aggregates in aged and cataractous lens nuclear cytoplasm compared to the dense protein packing in the cores of MLBs. Thin sections, 70 nm thick, were prepared from epoxy-embedded human transparent donor lenses and nuclear cataracts. Tilt series were collected on an FEI T20 transmission electron microscope (TEM) operated at 200 kV using 15 nm gold particles as fiducial markers. Images were aligned and corrected with FEI software and reconstructed with IMOD and other software packages to produce animated tilt series and stereo anaglyphs. The 3D views of protein density showed the relatively uniform packing of proteins in aged transparent lens nuclear cytoplasm and less dense packing of aged cataractous cytoplasm where many low-density regions can be appreciated in the absence of the TEM projection artifacts. In contrast the cores of the MLBs showed a dense packing of protein with minimal density fluctuations. These observations support the conclusion that, during the nuclear cataract formation, alterations in protein packing are extensive and can result in pronounced density fluctuations. Aging causes the MLB cores to become increasingly different in their protein packing from the adjacent cytoplasm. These results support the hypothesis that the MLBs increase their scattering with age and nuclear cataract formation.

Systematic infrared ablations with the mark III FEL at 2.94 μm in the chicken cornea

Abstract Introduction. Previous studies with the free electron laser have only assessed the corneal tissue response in ex vivo models. This is the first free electron laser investigation that has examined the clinical and histologic response of the cornea in vivo . Methods. The Mark III free electron laser was tuned to 2.94 μm for a total of 212 separate in vivo 1 mm spot ablations at varied fluences (0.4–2.04 J/cm 2 ), repetition rates (1–15 Hz), and number of pulses (1–32). Also, 22 separate in vivo central scanning patterns were performed. Results. For the in vivo chicken cornea, the threshold of ablation is approximately 0.64 J/cm 2 at a repetition rate of 10 Hz. Clinical biomicroscopy and light microscopy revealed parameter-dependent collateral damage (10–40) μm) induced by laser energy. Wound healing following free electron laser ablation exhibits patterns similar to those seen in excimer laser anterior keratectomy, including increased epithelial thickness, new collagen deposition, increased numbers of keratocytes, and patterns congruent with attempted profiles of myopic ablation. Conclusions. With further study, continued parameter adjustment, and refined delivery schemes, the potential for marked improvement and possible application appears promising.

Keratouveitis from Euphorbia cyparissias exposure is a temporal phenomenon

We present the case of an 82-year-old woman with severe keratouveitis secondary to exposure to the plant Euphorbia cyparissias during the month of August. Despite copious irrigation of both eyes, she developed a case of Euphorbia keratouveitis that was typical in its course. Exposure to plant sap from this species should be treated much like an alkaline chemical injury as the pH of the ocular surface may be elevated. E. cyparissias should be carefully handled as it may result in keratouveitis, especially in early autumn.