Many clinical studies have shown that, during periods between blinks, the tear film does not remain uniform on the surface of the eye. Subjects fixated using the nontested eye on a distant fixation target and suspended blinking as long as possible. Liang J, Williams DR. Using a clinical slit lamp biomicroscope, we alternated between wide-field blue and narrow beam white light to obtain an interleaved series of FL and RI images of the time course and pattern of tear film break-up. The fluorescein method has also been used to monitor the time course and spatial patterns of tear film disruption during periods of non-blinking. Such close agreement is remarkable given that the RI and FL images were not obtained at precisely the same time, and there are many unknown parameters of the slit lamp optics that will determine the exact relationship between RI intensity and local slope of the tear film. For any point S or T lying between U and R, a portion of the rays will enter the camera aperture depending on how close each corneal point is to the lower and upper extremes.
Oxford University Press, The front surface of the precorneal tear film is the most anterior optical surface of the eye. The tear film was monitored under two experimental conditions: Invest Ophthalmol Vis Sci ; submitted. However, before comparing the two images quantitatively, it is worth reassessing the precise theoretical relationship between these two types of images. B An eccentric light source causes some reflected rays to miss the camera aperture, resulting in a non-uniform intensity profile across the RI image see insert. Three samples are shown in Fig.
This suggests that differences between studies may be due to inter-subject variability in tear break-up. J Opt Soc Am A ;submitted: Local ray bundles can be deviated toward or away from the entrance pupil of the slit lamp biomicroscope and therefore result in fi,m patches brighter or darker than average in the RI image Figs.
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Areas lacking fluorescence dark areas are interpreted as local gaps or thinning refroillumination the tear film. In conclusion, RI may be used clinically in the diagnosis and management of dry eye, particularly in the assessment of the tear film in soft contact lens wearers.
As discussed by Himebaugh et al. B An eccentric light source causes some reflected rays to miss the camera aperture, resulting in a non-uniform intensity profile across the RI image see insert.
All three methods were applied continuously during extended periods of nonblinking both with and without soft contact lenses on the eye. The effect of tear film break-up on the optical aberrations and light scatter hear the eye.
You will receive an email whenever this article is corrected, updated, or cited in the literature. Second, we have observed subjects in our laboratory who fail to show tear break-up up to 1 minute after a blink, and thus the inter-study difference may simple reflect inter-subject differences in the stability of tears.
Figure 1C shows the rays exiting at S being deviated toward the base of the prism and away from the camera aperture. However, instillation of fluorescein into the eye may alter the dynamics of the tears, which can influence tear stability and break-up. Optom Vis Sci ; View Original Download Slide. The decline in image quality can be readily seen in the fundus images and the accompanying intensity profiles.
USE OF RETROILLUMINATION TO VISUALIZE OPTICAL ABERRATIONS CAUSED BY TEAR FILM BREAK-UP
The subject first blinked at 58 seconds, and we continued to monitor this eye during four minutes of normal blinking to examine the time course and spatial characteristics of the tear film recovery.
The aim of the teear study was to develop quantitative methods to assess optical aberrations caused by tear film disruption.
It appears to thin or disrupt locally, a phenomenon clinically termed tear film break-up. The nontested eye was covered with a contact eye patch. The technique has many optical similarities to the Foucault retriollumination 22 and, more specifically, to eccentric photorefraction. The large refractive index step from air to the tears provides this surface with the greatest optical power of any ocular surface.
Tear film lipid layer thickness as a function of blinking. Optical quality of the eye was assessed during periods of nonblinking by quantifying vessel contrast in the fundus image and by monitoring the psychophysical contrast sensitivity and the spatial distribution of tear thickness changes by retroillumination.
A standard clinical technique for evaluating tear film break-up involves instilling trar fluorescein dye into the eye. Therefore, the spatial derivative of the FL images along the x direction should mirror the RI intensity fluctuations in the horizontal meridian.
The precorneal tear film: In order to get a complete two-dimensional map retroi,lumination the local slope changes two orthogonal light sources are required. As predicted by optical analysis of RI, the spatial distribution of gaps in the tear film seen with fluorescein appeared as retroillumjnation of light and dark contours in the RI images, and a precise correspondence between the spatial derivative of the FL image slope and the RI image was found.
In the case of contact lens wear, it has been suggested that psychophysical losses of low-contrast acuity 9 or light scattering 12 associated with periods of nonblinking in eyes wearing SCL Fig.
Create an Account or Subscribe Now. We have employed the RI filk previously to visualize the spatial pattern of refractive changes induced by thinning of the tear film and to correlate those patterns with aberration maps and fluorescein maps of tear film thickness.
Optical and Visual Impact of Tear Break-up in Human Eyes | IOVS | ARVO Journals
Intensity fluctuations in the RI images are retroilluumination to thickness changes in the tear film, whereas intensity fluctuations in FL images are directly determined by tear film thickness. Retroillumination of the tear film during breakup Abstract.
The qualitative correspondence seen in the RI and FL images is not surprising since both methods are monitoring the same tear break-up.