Medical devices; ophthalmic devices; classification of the eyelid thermal pulsation system. Final rule

The Food and Drug Administration (FDA) is classifying the eyelid thermal pulsation system into class II (special controls). The Agency is classifying the device into class II (special controls) in order to provide a reasonable assurance of safety and effectiveness of the device.

An inexpensive and easy simulation model of ocular ultrasound that mimics normal anatomy as well as abnormal ophthalmologic conditions

We have constructed a simple and inexpensive simulation model for the educational instruction of health care providers to detect normal and abnormal ocular conditions in the bedside emergency setting. Such a training model serves to increase the comfort level in performing ocular ultrasound examinations and can increase the accuracy of examination interpretation. Ophthalmologic examinations can be difficult in the emergency setting, and ultrasound has become a useful tool in the diagnosis of emergent ocular conditions.

A new universal rat restrainer for ophthalmic research

PURPOSE

Immobilization of rats is required in many psychological and physiological experiments. The aim of the current paper was to invent a universal device allowing for adaptation of rats of a wide age range and to maximize convenience for in vivo exposure to optical radiation under not-anaesthetized conditions.

METHODS

Eighty-three 6-week-old and three 18-week-old Sprague-Dawley albino female rats were progressively familiarized daily with the restraining device 5 days prior to exposure to acquire a conditioned response and to reduce stress. After initial habituation, 10 min preceding the ultraviolet radiation (UVR) exposure, the animal was fixed in the rat restrainer. Each unanaesthetized animal was unilaterally exposed to a single dose of 8 kJ/m² UVR-300 nm for 15 min. Three of the 6-week-old and three of the 18-week-old rats were in vivo exposed to UVR once for 10 consecutive days.

RESULTS

All rats acclimatized well to immobilization in the restrainer. Young rats adapted quicker than older rats. The device prevented head movement and body rotation, which allowed for uncomplicated single as well as repeated in vivo exposures to UVR.

CONCLUSIONS

The restrainer effectively immobilizes unanaesthetized rats in the age range 6-18 weeks old, making it useful in future projects involving chronic repeated in vivo exposure of the eye to UVR.

[Interesting life father's of Polish ophthalmology--Wiktor Feliks Szokalski (1811-1891)--in 200 years anniversary of his birth]

Victor Szokalski is considered to be the father of Polish ophthalmology. He was born in Warsaw in 1811, where he also began his medical studies. He fought in the November's Uprising. He was awarded the Military Cross Virtuti. After its fall he went to Germany, where he continued his studies. In 1834 he defended his doctoral thesis. Then he moved to France, where worked at the Eye Clinic of Jules Sichel. He wrote many articles for medical journals and taught students. Already in Paris he acted in a number of social societies, collaborated with Prince Adam Czartoryski, was a friend of Adam Mickiewicz. Fifteen years later he returned to Warsaw, where became a consultant, then the chief at the Ophthalmic Institute. For 33 years he has served as secretary of the Warsaw Medical Society. He wrote the first Polish original textbook of ophthalmology. He died in Warsaw in 1891.

Use of laser speckle flowgraphy in ocular blood flow research

Laser speckle flowgraphy (LSFG) allows for the quantitative estimation of blood flow in the optic nerve head, choroid, retina and iris in vivo. It was developed to facilitate the non-contact analysis of ocular blood flow in living eyes, utilizing the laser speckle phenomenon. The technique uses a fundus camera, a diode laser, an image sensor, an infrared charge-coupled device (CCD) camera and a high-resolution digital CCD camera. Normalized blur (NB), an approximate reciprocal of speckle contrast, represents an index of blood velocity, and shows a good correlation with tissue blood flow rates determined with the microsphere method in the retina, choroid or iris, as well as blood flow rates determined with the hydrogen gas clearance method in the optic nerve head. The square blur ratio (SBR), another index for quantitative estimation of blood velocity, is proportional to the square of the NB. The SBR is theoretically a more exact measurement which is proportional to velocity, whereas the NB is an approximation. Normalized blur was calculated in earlier versions of LSFG because of technical limitations; the SBR is used in current versions of the LSFG instrument. As these values are in arbitrary units, they should not be used to make comparisons between different eyes or different sites in an eye. Clinical protocols, calibration, evaluation procedures and possible limitations of the LSFG technique are described and the results of ocular blood flow studies using LSFG are briefly summarized. The LSFG method is suitable for monitoring the time-course of change in the tissue circulation at the same site in the same eye at various intervals, ranging from seconds to months. Unresolved issues concern the effect of pupil size on measurement results, the effects of various stimulations, and how to measure choroidal and retinal blood flow velocity separately without using the blue-component of argon laser.

Use of laser speckle flowgraphy in ocular blood flow research

Laser speckle flowgraphy (LSFG) allows for the quantitative estimation of blood flow in the optic nerve head, choroid, retina and iris in vivo. It was developed to facilitate the non-contact analysis of ocular blood flow in living eyes, utilizing the laser speckle phenomenon. The technique uses a fundus camera, a diode laser, an image sensor, an infrared charge-coupled device (CCD) camera and a high-resolution digital CCD camera. Normalized blur (NB), an approximate reciprocal of speckle contrast, represents an index of blood velocity, and shows a good correlation with tissue blood flow rates determined with the microsphere method in the retina, choroid or iris, as well as blood flow rates determined with the hydrogen gas clearance method in the optic nerve head. The square blur ratio (SBR), another index for quantitative estimation of blood velocity, is proportional to the square of the NB. The SBR is theoretically a more exact measurement which is proportional to velocity, whereas the NB is an approximation. Normalized blur was calculated in earlier versions of LSFG because of technical limitations; the SBR is used in current versions of the LSFG instrument. As these values are in arbitrary units, they should not be used to make comparisons between different eyes or different sites in an eye. Clinical protocols, calibration, evaluation procedures and possible limitations of the LSFG technique are described and the results of ocular blood flow studies using LSFG are briefly summarized. The LSFG method is suitable for monitoring the time-course of change in the tissue circulation at the same site in the same eye at various intervals, ranging from seconds to months. Unresolved issues concern the effect of pupil size on measurement results, the effects of various stimulations, and how to measure choroidal and retinal blood flow velocity separately without using the blue-component of argon laser.

Retinal imaging with polarization-sensitive optical coherence tomography and adaptive optics

Various layers of the retina are well known to alter the polarization state of light. Such changes in polarization may be a sensitive indicator of tissue structure and function, and as such have gained increased clinical attention. Here we demonstrate a polarization-sensitive optical coherence tomography (PS-OCT) system that incorporates adaptive optics (AO) in the sample arm and a single line scan camera in the detection arm. We quantify the benefit of AO for PS-OCT in terms of signal-to-noise, lateral resolution, and speckle size. Double pass phase retardation per unit depth values ranging from 0.25 degrees/microm to 0.65 degrees/microm were found in the birefringent nerve fiber layer at 6 degrees eccentricity, superior to the fovea, with the highest values being noticeably higher than previously reported with PS-OCT around the optic nerve head. Moreover, fast axis orientation and degree of polarization uniformity measurements made with AO-PS-OCT demonstrate polarization scrambling in the retinal pigment epithelium at the highest resolution reported to date.

Association between corneal hysteresis and central corneal thickness in glaucomatous and non-glaucomatous eyes

PURPOSE

We aimed to determine corneal hysteresis values (CH) using the ocular response analyser (ORA) in non-glaucomatous and glaucomatous eyes and their relationship with central corneal thickness (CCT).

METHODS

Corneal hysteresis, intraocular pressure (IOP) as measured by Goldmann applanation tonometry (GAT) and CCT were prospectively evaluated in 74 non-glaucoma subjects with IOP < 21 mmHg and in 108 patients with treated primary open-angle glaucoma (POAG). One eye in each subject was randomly selected for inclusion in the analysis.

RESULTS

Mean (+/- standard deviation [SD]) age was 59.2 +/- 14.2 years in the non-glaucoma group and 62.4 +/- 9.8 years in the glaucoma group. Mean (+/- SD) GAT IOP was 15.7 +/- 2.65 mmHg and 16.38 +/- 2.73 mmHg in the non-glaucoma and glaucoma groups, respectively. There was no statistically significant difference between the two groups in mean age (p = 0.396) or mean GAT IOP (p = 0.098). Mean (+/- SD) CH was 10.97 +/- 1.59 mmHg in the non-glaucoma and 8.95 +/- 1.27 mmHg in the glaucoma groups, respectively. The difference in mean CH between the two groups was statistically significant (p < 0.0001). There was a strong positive correlation between CH and CCT in the non-glaucoma group (r = 0.743) and a significantly (p = 0.001) weaker correlation (r = 0.426) in the glaucoma group.

CONCLUSIONS

Corneal hysteresis was significantly lower in eyes with treated POAG than in non-glaucomatous eyes. The corneal biomechanical response was strongly associated with CCT in non-glaucoma subjects, but only moderately so in glaucoma patients. It can be assumed that diverse structural factors, in addition to thickness, determine the differences in the corneal biomechanical profile between non-glaucomatous and glaucomatous eyes. Corneal hysteresis could be a useful tool in the diagnosis of glaucoma.

Sophisticated instrumentation and ophthalmic ultrasonography

Formerly, ophthalmic ultrasonography was leading in view of high-performance apparatuses and transducer probes: e.g., the first array-scanner in the world was built for ophthalmic use. Within the past 2 decades, however, high-tech innovations were merely developed for other medical specialties. These were studied in view of their use for ultrasonography of eye and orbit. The combination of B-scan and Doppler techniques facilitates detection of orbital vessels. The resolution of ophthalmic digital B-scan video images proved poorer than crt-B-scans. A digital memory, however, is advantageous. But one high-resolution crt-type B-scan needs more than one disc storage capacity. "Frontline digitalization" could help to reduce the amount of data. Array transducers are now available in small sizes and could better show structure movements, but they were not yet adapted to ophthalmic use. This applies as well to annular arrays and dynamic focusing. Different methods of 3-dimensional scanning and (Pseudo-) 3-dimensional imaging might renew Baum's and Coleman's early work.

Dual-conjugate adaptive optics for wide-field high-resolution retinal imaging

We present analysis and preliminary laboratory testing of a real-time dual-conjugate adaptive optics (DCAO) instrument for ophthalmology that will enable wide-field high resolution imaging of the retina in vivo. The setup comprises five retinal guide stars (GS) and two deformable mirrors (DM), one conjugate to the pupil and one conjugate to a plane close to the retina. The DCAO instrument has a closed-loop wavefront sensing wavelength of 834 nm and an imaging wavelength of 575 nm. It incorporates an array of collimator lenses to spatially filter the light from all guide stars using one adjustable iris, and images the Hartmann patterns of multiple reference sources on a single detector. Zemax simulations were performed at 834 nm and 575 nm with the Navarro 99 and the Liou- Brennan eye models. Two correction alternatives were evaluated; conventional single conjugate AO (SCAO, using one GS and a pupil DM) and DCAO (using multiple GS and two DM). Zemax simulations at 575 nm based on the Navarro 99 eye model show that the diameter of the corrected field of view for diffraction-limited imaging (Strehl >or= 0.8) increases from 1.5 deg with SCAO to 6.5 deg using DCAO. The increase for the less stringent condition of a wavefront error of 1 rad or less (Strehl >or= 0.37) is from 3 deg with SCAO to approximately 7.4 deg using DCAO. Corresponding results for the Liou-Brennan eye model are 3.1 deg (SCAO) and 8.2 deg (DCAO) for Strehl >or= 0.8, and 4.8 deg (SCAO) and 9.6 deg (DCAO) for Strehl >or= 0.37. Potential gain in corrected field of view with DCAO is confirmed both by laboratory experiments on a model eye and by preliminary in vivo imaging of a human eye.

Adjustable fluidic lenses for ophthalmic corrections

We report on two fluidic lenses that have been developed for ophthalmic applications. The lenses use a circular aperture to demonstrate optical powers between -20 and +20 D and a rectangular aperture to demonstrate astigmatism with values ranging from 0 to 8 D. Measurements of image quality were made with the fluidic lens using a model eye. Both lenses were variable and controllable by adjusting the fluid volume of the lens. To the best of our knowledge this is the first demonstration of a continuously variable lens for control of astigmatism.