Optical Quality of the Eye Degraded by Time-Varying Wavefront Aberrations with Tear Film Dynamics

Successful Detection of the Characteristics of Tear Film Breakup Appearing Immediately after Eye Opening by Videokeratography with a Newly-Developed Indicator

Spot break (SB), a tear film breakup (TFBU) subtype seen in decreased wettability dry eye (DE), is characterized by a spot-like TFBU that appears immediately after eye opening. It is sometimes difficult to detect using currently available devices for evaluating non-invasive TFBU. The purpose of this study was to investigate the effectiveness of using a newly developed videokeratography indicator for detecting SB. The study involved 44 eyes of 44 DE patients (21 eyes with SB (SB group) and 23 eyes with random break in which fluorescein breakup time was ≤ 5 s (s) (RB group)). All eyes were examined using videokeratography, with digital Meyer-ring images being obtained. By calculation of the degree of luminance blur on the cornea in the Meyer-ring images, termed ‘disturbance value’ (DV), DVs at 0 s (DV(0)]), 2 s (DV(2)), and 5 s (DV(5)) after eye opening, and the changes of DV between each time, were compared between the SB and RB groups. Results: No significant differences in DV(2) and DV(5) and the rate of change between DV(2) and DV(5) were found between the two groups. However, DV(0) and rate of change between DV(0) and DV(2) in the SB group were significantly greater (p < 0.001) than those in the RB group. SB characteristics were successfully detected by videokeratography using a new videokeratography DV indicator.

Irregular Astigmatism and Higher-Order Aberrations in Eyes With Dry Eye Disease

Visual disturbances were included in the definition of dry eye disease in the 2007 Dry Eye Workshop report. As a result, quality of vision (QoV) in dry eye patients has received increased attention. Corneal topography and wavefront sensors have been used to objectively and quantitatively evaluate optical quality, with data showing increases in irregular astigmatism and higher-order aberrations (HOAs) in dry eye patients. Furthermore, ocular optical characteristics are influenced by the tear film, which constantly fluctuates over time. Therefore, dynamic quantitative assessments of optical quality with continuous measurements are essential to understanding QoV in dry eye patients. This review summarizes what is known and what advances have been made in evaluating and understanding QoV in dry eye patients. In particular, corneal topographic and wavefront analyses, conducted both overseas and in Japan, are described.

Effects of tear film dynamics on quality of vision

The precorneal tear film is maintained by blinking and exhibits different phases in the tear cycle. The tear film serves as the most anterior surface of the eye and plays an important role as a first refractive component of the eye. Alterations in tear film dynamics may cause both vision-related and ocular surface-related symptoms. Although the optical quality associated with the tear film dynamics previously received little attention, objective measurements of optical quality using wavefront sensors have enabled us to quantify optical aberrations induced by the tear film. This has provided an objective method for assessing reduced optical quality in dry eye; thus, visual disturbances were included in the definition of dry eye disease in the 2007 Dry Eye Workshop report. In addition, sequential measurements of wavefront aberrations have provided us with valuable insights into the dynamic optical changes associated with tear film dynamics. This review will focus on the current knowledge of the mechanisms of wavefront variations that are caused by different aspects of tear film dynamics: specifically, quality, quantity and properties of the tear film, demonstrating the respective effects of dry eye, epiphora and instillation of eye drops on the quality of vision.

Mechanisms of Visual Disturbance in Dry Eye

Dry eye has been believed to be a chronic, symptomatic ocular surface disease that affects vision in a limited manner, because it is difficult to detect visual or optical changes using standard visual acuity testing. In practice, common visual complaints associated with dry eye include fluctuating vision with blinking, blurred vision, glare, and eye fatigue. This review discusses our past and current understanding of visual disturbances in dry eye and the various tools available for assessing visual function or optical quality. Tear film instability and ocular surface damage are key factors in the core mechanism underlying dry eye. The mechanisms of these vision-related subjective symptoms of dry eye based on visual function, particularly wavefront aberrations or light scattering, and the core mechanism of dry eye are described. Tear film instability is associated with decreased stability of postblink higher-order aberrations, leading to "fluctuating vision with blinking" and with increased ocular forward light scattering, leading to "glare." Ocular surface damage in the overlying optical zone (in the central corneal regions), is associated with increased higher-order aberrations and increased corneal backward light scattering that can lead to "blurred vision". "Eye fatigue" occurs when patients with dry eye struggle to see things under such visual symptoms.

Measurement of the time course of optical quality and visual deterioration during tear break-up

PURPOSE

To compare changes in optical quality and visual performance that accompany tear break-up (TBU) during blink suppression.

METHODS

A three-channel optical system was developed that simultaneously measured refractive aberrations (Shack-Hartmann aberrometer), 20/40 letter contrast sensitivity (CS), and TBU (retroillumination, RI). Ten wearers of silicone hydrogel contact lenses were asked to keep one eye open for approximately 18 seconds, while CS, wavefront aberrations, and RI images were collected. The wavefront was reconstructed by zonal methods, and image quality was quantified with a series of metrics including RMS fit error. Novel metrics for quantifying TBU over the contact lens surface were developed by quantifying the contrast of the RI image and by using Fourier descriptors of the first Purkinje (PJ) image shape.

RESULTS

There was a full range of TBU over the lens surface, with four subjects showing TBU across the corneal center and one subject with TBU in the inferior peripheral pupil. Among the four subjects with central corneal TBU, RMS fit error, RI contrast, and PJ Fourier descriptors showed high correlation with CS (r(2) range, 0.9187-0.9414, 0.6261-0.975, and 0.4917-0.8986, respectively). Some of the general optical-quality metrics such as blur strength, neural sharpness, and area of modulation transfer function (MTF) also showed that change correlated with CS loss.

CONCLUSIONS

Optical metrics of tear quality and retinal image quality are associated with the decline in vision that occurs with TBU. The evidence supports the hypothesis that blurry vision symptoms reported by contact lens wearers are caused by poor quality of the retinal image due to TBU.

Relationship between myopia and allergen-specific serum IgE levels in patients with allergic conjunctivitis

PURPOSE

Various exogenous allergens can cause allergic conjunctivitis, whereas refractive errors are also related (as an endogenous factor) to the pathogenesis of allergic conjunctivitis. However, little is known about the interaction between exogenous and endogenous factors in patients with allergic conjunctivitis. We investigated the relationship between refractive errors and exogenous allergens in patients with allergic conjunctivitis.

METHODS

Sixty patients with allergic conjunctivitis and 60 healthy subjects (non-allergy patients) were enrolled. Refraction was carried out in all subjects. In addition, total immunoglobulin E (IgE) and specific IgE levels for 12 inhaled allergens were measured by the capsulated hydrolic carrier polymer system.

RESULTS

The patients who were positive for-specific IgE to indoor allergens had higher myopia than those who were negative, including those positive for house dust IgE (-3.66 +/- 2.95 vs. -1.05 +/- 3.39, P = 0.0015), Dermatophagoides pteronyssinus (D. pteronyssinus) IgE (-3.50 +/- 2.91 vs. -1.01 +/- 3.46, P = 0.0021), and acarus IgE (-3.45 +/- 2.21 vs. -1.51 +/- 3.73, P = 0.0087), whereas antibody-positive and antibody-negative patients for outdoor allergens showed no significant differences of refraction. Refractions in indoor group (-3.58 +/- 3.42) and indoor/outdoor (-3.70 +/- 2.64) group were higher than those in outdoor group (-0.84 +/- 2.30, P = 0.0047 and P = 0.0032) and the non-allergy group (-1.30 +/- 1.48, P = 0.0082 and P = 0.0054) [-refraction] was significantly correlated with total IgE (r = 0.333, P = 0.0093), house dust (r = 0.355, P = 0.0054) and D. pteronyssinus (r = 0.379, P = 0.0028), while no correlation between refractive error and outdoor allergens was proven.

CONCLUSION

These results suggest that specific IgE levels for indoor allergens, such as house dust, might be associated with refractive errors.