Recently, a technique known as cornea-specific in vivo laser confocal microscopy that uses a diode laser with a wavelength of 670 nm has been developed, which has enabled less-invasive high-resolution in vivo observation of the corneal microstructure at the cellular level (in vivo biopsy). Acanthamoeba keratitis (AK) is an intractable corneal infection that is common among contact lens users. Clinical diagnosis of the disease is very difficult, especially in the early phase. The condition is often misdiagnosed and treated as a herpes simplex infection. An early diagnosis is of paramount importance because commencing treatment soon after onset improves the prognosis of visual acuity. Acanthamoeba cysts can be observed in the epithelium with the aid of in vivo confocal microscopy as a circular high-intensity material with a diameter of 10-20 μm, which enables a minimally invasive and rapid auxiliary diagnosis. When we observed radial keratoneuritis, which is characteristic of AK, we found only inflammatory findings around the corneal nerve and no infiltrative findings of the amoeba itself. Furthermore, by using anterior segment optical coherence tomography, we visualized the radial keratoneuritis as a linear lesion within the parenchyma. Even in cases where radial keratoneuritis is difficult to observe with a slit-lamp microscope owing to strong corneal opacity, it can be visualized with this system, which makes it extremely useful in auxiliary diagnosis.
Cytomegalovirus corneal endotheliitis is a disease caused by cytomegalovirus infection of the corneal endothelial cells and trabecular meshwork cells, which results in progressive corneal endothelial damage and intractable glaucoma. This disease was identified in Japan in 2006. With the use of confocal microscopy, owl's eye cells, a pathological finding characteristic of this disease, can be observed in vivo in a minimally invasive manner. We performed extensive mapping of the owl's-eye cells and found them to be in perfect agreement with the coin-shaped lesions observed by confocal microscopy.
In addition, confocal microscopy allows real-time observation of the biological tissues in various corneal dystrophies. We reported that this technique is extremely useful in the differential diagnosis and observation of the course of treatment in Bowman layer dystrophy (Reis-Bücklers corneal dystrophy, Thiel-Behnke corneal dystrophy) and other corneal dystrophies.
We used in vivo laser confocal microscopy to visualize the Bowman layer and its adjacent stroma in normal volunteers and demonstrated for the first time the presence of fibrous structures just beneath the Bowman layer. These fibrous structures designated as "Kobayashi-structure (K-structure)," were 5-15 μm in diameter and appeared to consist of many filaments with slightly lower brightness than the corneal subepithelial nerve. In Bowman layer dystrophy and advanced keratoconus, the K-structure disappeared. Subsequent to corneal refractive surgery, the K-structure was observed after laser in-situ keratomileusis (LASIK) in which the Bowman layer was preserved. However, the K-structure was lost after epipolis LASIK (epi LASIK) in which the Bowman layer was excised by the laser. The results suggested that the K-structure can be an indicator of health of Bowman layer. Furthermore, by extensive mapping, we found that the K-structure and corneal (fluorescein) mosaicism were in perfect agreement and that the K-structure was the anatomical cause of corneal (fluorescein) mosaicism.
On the other hand, the development of minimally invasive corneal transplantation has been remarkable. The only radical treatment for bullous keratopathy, the most severe disease associated with corneal endothelial disorder, was penetrating keratoplasty. However, Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK) were developed for the treatment of corneal endothelial dysfunction because of the progress of corneal parts transplantation, which enabled very minimally invasive treatment. However, the surgical techniques required for the DSAEK/DMEK procedure are quite challenging, especially for the eyes of Japanese people. The Japanese patients tend to have advanced bullous keratopathy with shallow anterior chambers, high vitreous pressure, and dark brown irises compared with western patients, and these factors often complicate DSAEK/DMEK. We developed a new technique (called the "double glide technique") that does not damage the donor endothelium. We also developed the ultimate minimally invasive corneal endothelial transplantation without stripping the Descemet membrane and named it non-DSAEK (nDSAEK). Furthermore, we found that the use of vitreous illumination is useful in improving donor visibility during DMEK. We also developed a DMEK graft grasping technique that allows quick and minimally invasive deployment of the DMEK graft in the anterior chamber. With the development of these techniques and peripheral devices, DSAEK/DMEK has now evolved into a safe procedure with fewer complications.
Nippon Ganka Gakkai Zasshi (J Jpn Ophthalmol Soc) 126: 326-357,2022.