Visual Discrimination Increase by Yellow Filters in Retinitis Pigmentosa

PURPOSE

The objective of this study was to evaluate, by halometry and under low illumination conditions, the effects of short-wavelength light absorbance filters on visual discrimination capacity in retinitis pigmentosa patients.

METHODS

This was an observational, prospective, analytic, and transversal study on 109 eyes of 57 retinitis pigmentosa patients with visual acuity better than 1.25 logMAR. Visual disturbance index (VDI) was determined using the software Halo 1.0, with and without the interposition of filters which absorb (totally or partially) short-wavelength light between 380 and 500 nm.

RESULTS

A statistically significant reduction in the VDI values determined using filters which absorb short-wavelength light was observed (p < 0.0001). The established VDIs in patients with VA logMAR <0.4 were 0.30 ± 0.05 (95% CI, 0.26-0.36) for the lens alone, 0.20 ± 0.04 (95% CI, 0.16-0.24) with the filter that completely absorbs wavelengths shorter than 450 nm, and 0.24 ± 0.04 (95% CI, 0.20-0.28) with the filter that partially absorbs wavelengths shorter than 450 nm, which implies a 20 to 33% visual discrimination capacity increase. In addition, a decrease of VDI in at least one eye was observed in more than 90% of patients when using a filter.

CONCLUSIONS

Short-wavelength light absorbance filters increase visual discrimination capacity under low illumination conditions in retinitis pigmentosa patients. Use of such filters constitutes a suitable method to improve visual quality related to intraocular light visual disturbances under low illumination conditions in this group of patients.

Night vision disturbances after corneal refractive surgery

A certain percentage of patients complain of "glare" at night after undergoing a refractive surgical procedure. When patients speak of glare they are, technically, describing a decrease in quality of vision secondary to glare disability, decreased contrast sensitivity, and image degradations, or more succinctly, "night vision disturbances." The definitions, differences, and methods of measurement of such vision disturbances after refractive surgery are described in our article. In most cases of corneal refractive surgery, there is a significant increase in vision disturbances immediately following the procedure. The majority of patients improve between 6 months to 1 year post-surgery. The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved. Treatment options for disabling glare are also discussed. With the exponential increase of patients having refractive surgery, the increase of patients complaining of scotopic or mesopic vision disturbances may become a major public health issue in the near future. Currently, however, there are no gold-standard clinical tests available to measure glare disability, contrast sensitivity, or image degradations. Standardization is essential for objective measurement and follow-up to further our understanding of the effects of these surgeries on the optical system and thus, hopefully, allow for modification of our techniques to decrease or eliminate post-refractive vision disturbances.

Is Abnormal Focal Steepening of the Cornea Related to Persistent Monocular Diplopia?

PURPOSE

Some case reports have shown that abnormal focal steepening of the cornea appears to cause monocular diplopia by prismatic effect. The purpose of this study was to ascertain prospectively if the pattern of corneal distortion was related specifically to persistent monocular diplopia.

METHODS

We selected 16 visually normal eyes (controls) and two groups of volunteers in which abnormal focal steepening of the cornea was expected to be found: 40 eyes of 20 volunteers who wore rigid gas-permeable contact lenses (RGP) for myopia and 10 eyes of seven patients with keratoconus. New charts that consisted of white dials on a black background were prepared for detection and measurement of secondary images. Any secondary image that could not be eliminated by any trial lens correction was defined as a persistent secondary image, using the charts. Corneal topography from all subjects was classified: round or oval, symmetric or asymmetric bowtie, abnormal focal steepening accompanied by contact lens-induced corneal warpage or keratoconus, or amorphous. We analyzed the relationship between the persistent secondary image and the corneal topographical patterns.

RESULTS

A persistent secondary image was detected from seven eyes of RGP wearers and all keratoconus eyes. All corneal topographies of the seven RGP eyes with a persistent secondary image showed abnormal focal steepening related to contact lens-induced corneal warpage. The direction of the persistent secondary image was approximately consistent with the location of the focal steepening as seen on the corneal topography.

CONCLUSION

Abnormal focal steepening of the cornea that appeared to produce a prismatic difference between two parts of the cornea was specifically related to persistent monocular diplopia.

An in vivo investigation of the structures responsible for corneal haze after photorefractive keratectomy and their effect on visual function

PURPOSE

To make serial measurements of corneal haze and microscopic anatomy after photorefractive keratectomy (PRK) and compare the results with visual function measured at the same time points in the same single group of human subjects.

METHODS

Ten patients underwent -6.00-diopter, 6-mm PRK. The patients were reviewed frequently for 12 months. Corneal haze was measured objectively in two ways: (1) an opacification index was determined from the variance in digitized retroillumination images; and (2) light reflected and scattered back from the cornea was assessed by gray-scale analysis of video slit images. In vivo confocal microscopy recorded the anatomic changes occurring in the cornea, and computer analysis of the images quantified the keratocytes and subepithelial deposit. Visual performance was assessed by Snellen visual acuity, contrast sensitivity, and glare-induced visual dysfunction.

RESULTS

In the first week, epithelial irregularity resulted in a transient reduction in all aspects of visual function. In the first month, keratocyte disturbances reduced contrast sensitivity at high frequencies and produced glare. Over the next couple of months, the subepithelial deposit resulted in a more prolonged loss of contrast sensitivity at low frequencies and glare-induced visual dysfunction due to the scattering of light. In several patients, these visual defects persisted after 1 year.

CONCLUSIONS

Epithelial and keratocyte disturbances only transiently affect visual function. The subepithelial deposit is more persistent and can have a lasting effect on visual performance. Therefore, attempts to improve the visual outcome of PRK must be aimed at controlling the synthesis of subepithelial material.

Night Vision Testing in Unoperated Eyes

BACKGROUND

We previously described a simple test which evaluates image degradation in post-excimer laser (PRK) patients under scotopic conditions. After refractive surgery, corneal haze, ablation zone decentration, ablation zone/pupillary diameter disparity, and under-correction each result in a characteristic pattern on the Night Vision Recording Chart.

METHODS

Using the same method, further studies evaluated night vision image degradation in 118 un-operated emmetropic, myopic, hyperopic, and astigmatic eyes and in 26 contact lens wearers.

RESULTS

Scotopic image degradation increases with myopic refractive error, image displacement increases with astigmatism, and contact lens wearers have more image degradation that with spectacle correction.

CONCLUSION

Our Night Vision Recording Chart offers a simple, reproducible method to characterize image degradation under scotopic conditions.