Augmented reality fundus biomicroscopy: a working clinical prototype.

BACKGROUND: To guide treatment for macular diseases and to facilitate real-time image correlation, measurement, and comparison, we developed a method for direct overlay of previously stored photographic and angiographic images onto the real-time slitlamp fundus view. METHODS: Previously acquired fundus photographs and angiography images were digitized. A slitlamp interfaced to a charge-coupled device camera, framegrabber, and computer allowed for real-time acquisition and digitization of slitlamp fundus images that was synchronous with posterior segment examination. Custom-developed video injectors containing a miniature cathode ray tube display allowed for real-time superposition of angiographic images to the fundus view. Registration and tracking algorithms were developed and deployed in C++. The feasibility of this approach was demonstrated in 5 human subjects. RESULTS: The computer-vision algorithms provided robust registration, tracking, and image overlay of previously stored photographic and angiographic images directly onto the real-time fundus view. Accurate tracking was demonstrated with updates at 3 to 5 Hz. Direct overlay of previously stored images confirmed registration accuracy, but examiners preferred a more simple rendering that included only relevant information and eliminated extraneous, potentially confusing image data. CONCLUSIONS: Slitlamp-based video injection of previously stored images allows for accurate, robust, real-time correlation and comparison to the biomicroscopic fundus view in human subjects.

Mosaicking and enhancement of slit lamp biomicroscopic fundus images.

AIMS: To process video slit lamp biomicroscopic fundus image sequences in order to generate wide field, high quality fundus image montages which might be suitable for photodocumentation. METHODS: Slit lamp biomicroscopic fundus examination was performed on human volunteers with a contact or non-contact lens. A stock, charge coupled device camera permitted image capture and storage of the image sequence at 30 frames per second. Acquisition time was approximately 30 seconds. Individual slit lamp biomicroscope fundus image frames were aligned and blended with custom developed software. RESULTS: The developed algorithms allowed for highly accurate alignment and blending of partially overlapping slit lamp biomicroscopic fundus images to generate a seamless, high quality, wide field montage. CONCLUSIONS: Video image acquisition and processing algorithms allow for mosaicking and enhancement of slit lamp biomicroscopic fundus images. The improved quality and wide field of view may confer suitability for inexpensive, real time photodocumentation of disc and macular abnormalities.

Automated, real time extraction of fundus images from slit lamp fundus biomicroscope video image sequences.

AIMS: Slit lamp fundus biomicroscopy allows for high magnification, stereoscopic diagnosis, and treatment of macular diseases. Variable contrast, narrow field of view, and specular reflections arising from the cornea, sclera, and examining lens reduce image quality; these images are of limited clinical utility for diagnosis, treatment planning, and photodocumentation when compared with fundus camera images. Algorithms are being developed to segment fundus imagery from slit lamp biomicroscopic video image sequences in order to improve clinical utility. METHODS: Video fundus image sequences of human volunteers were acquired with a video equipped, Nikon NS-1V slit lamp biomicroscope. Custom developed software identified specular reflections based on brightness and colour content, and extracted the illuminated fundus image based on colour image analysis and size constraints. RESULTS: In five subjects with variable image quality, the approach allowed for automatic, robust, accurate extraction of that portion of the video image corresponding to the illuminated portion of the fundus. Non-real time analysis allowed for fundus image segmentation for each frame of the image sequence. In real time, segmentation occurs at 2 Hz, and improvements are being implemented for video rate performance. CONCLUSIONS: Computer vision algorithms allow for real time extraction of fundus imagery from marginal quality, slit lamp fundus biomicroscope image sequences.

Choroidal concentration of interferon after retrobulbar injection.

PURPOSE: To determine whether recombinant human interferon alpha-2a (IFN alpha-2a) would diffuse into the choroid in significant amounts from a retrobulbar depot. METHODS: One million international units of IFN alpha-2a were injected into the retrobulbar space of the eyes of 17 rabbits, and choroidal and serum concentrations were measured at 1, 2, 4, 8, 12, and 24 hours. The same dose of IFN alpha-2a was injected subcutaneously into 10 rabbits, and choroidal and serum concentrations were measured at the same intervals for comparison. Parabulbar and ocular tissues were studied by light microscopy for evidence of local toxicity. RESULTS: Peak concentration IFN alpha-2a in the choroid after retrobulbar injection occurred at 2 hours and averaged 32,000 IU/mg. Peak concentration in the serum occurred at 4 hours and averaged 227 IU/ml. Concentrations in choroid and serum fell rapidly, and IFN alpha-2a was not detectible at 24 hours. No IFN alpha-2a was detected in the choroid of the paired eye, and only a trace (< 50 IU/mg) was found in either eye after subcutaneous injection. Light microscopy revealed some lymphocytes in the fat adjacent to the retrobulbar depot after six daily injections of IFN alpha-2a or saline. Sclera, choroid, and retina appeared unaffected. CONCLUSIONS: IFN alpha-2a diffuses into the choroid from a retrobulbar depot in significant amounts. The serum concentration from a retrobulbar injection is < 1% of the choroidal concentration. The retrobulbar route to the choroid may be optimal for testing the effect of IFN alpha-2a on choroidal neovascularization.

Safe method for cleaning the posterior lens capsule.

Cleaning the posterior capsule is an important step in cataract microsurgery to prevent early postoperative visual impairment. A simple method for cleaning posterior lens capsule opacities during extracapsular cataract extraction is described. A straight 20-gauge cannula with a 0.3 mm anterior aspiration port, attached to a syringe with the piston removed, allows safe polishing in a deep anterior chamber. The described procedure has been safely performed in more than 300 operations.

A new classification of the retinoschises.

BACKGROUND: Two classifications of retinoschisis were published in the 1960s. A marked expansion of our knowledge of the diseases that give rise to retinoschisis indicates the need for an updated classification. METHODS: The new classification is based on the authors' clinical experience, an extensive review of the literature, and a survey of 20 vitreoretinal specialists. RESULTS: There are three types of retinoschisis: degenerative, hereditary, and secondary. Degenerative retinoschisis is very common and has been published extensively. In addition to the well known X-linked hereditary retinoschisis, there are less common pedigrees with autosomal recessive or autosomal dominant patterns. There are at least 18 ocular diseases that may show varying degrees of secondary retinoschisis. CONCLUSION: The many types of retinoschisis are divided into these major categories. The multiplicity of types is emphasized by the plural form of the term: "the retinoschises."