David Alonso-Caneiro

Choroidal thickness in childhood.

PURPOSE We examined choroidal thickness (ChT) and its spatial distribution across the posterior pole in pediatric subjects with normal ocular health and minimal refractive error. METHODS ChT was assessed using spectral domain optical coherence tomography (OCT) in 194 children aged 4 to 12 years, with spherical equivalent refractive errors between +1.25 and -0.50 diopters sphere (DS). A series of OCT scans were collected, imaging the choroid along 4 radial scan lines centered on the fovea (each separated by 45°). Frame averaging was used to reduce noise and enhance chorioscleral junction visibility. The transverse scale of each scan was corrected to account for magnification effects associated with axial length. Two independent masked observers segmented the OCT images manually to determine ChT at foveal center, and averaged across a series of perifoveal zones over the central 5 mm. RESULTS The average subfoveal ChT was 330 ± 65 μm (range, 189-538 μm), and was influenced significantly by age (P = 0.04). The ChT of the 4- to 6-year-old age group (312 ± 62 μm) was significantly thinner compared to the 7- to 9-year-olds (337 ± 65 μm, P < 0.05) and bordered on significance compared to the 10- to 12-year-olds (341 ± 61 μm, P = 0.08). ChT also exhibited significant variation across the posterior pole, being thicker in more central regions. The choroid was thinner nasally and inferiorly compared to temporally and superiorly. Multiple regression analysis revealed age, axial length, and anterior chamber depth were associated significantly with subfoveal ChT (P < 0.001). CONCLUSIONS ChT increases significantly from early childhood to adolescence. This appears to be a normal feature of childhood eye growth.

Choroidal Thickness in Myopic and Nonmyopic Children Assessed With Enhanced Depth Imaging Optical Coherence Tomography

PURPOSE We examined choroidal thickness (ChT) and its topographic variation across the posterior pole in myopic and nonmyopic children. METHODS A total of 104 children aged 10 to 15 years (mean age, 13.1 ± 1.4 years) had ChT measured using enhanced depth imaging optical coherence tomography (OCT). Of these children 40 were myopic (mean spherical equivalent, -2.4 ± 1.5 diopters [D]) and 63 were nonmyopic (mean, +0.3 ± 0.3 D). Two series of 6 radial OCT line scans centered on the fovea were assessed for each child. Subfoveal ChT and ChT across a series of parafoveal zones over the central 6 mm of the posterior pole were determined through manual image segmentation. RESULTS Subfoveal ChT was significantly thinner in myopes (mean, 303 ± 79 μm) compared to nonmyopes (mean, 359 ± 77 μm, P < 0.0001). Multiple regression analysis revealed refractive error (r = 0.39, P < 0.001) and age (r = 0.21, P = 0.02) were associated positively with subfoveal ChT. Also, ChT exhibited significant topographic variations, with the choroid being thicker in more central regions. The thinnest choroid was observed typically in nasal (mean, 286 ± 77 μm) and inferior-nasal (306 ± 79 μm) locations, and the thickest in superior (346 ± 79 μm) and superior-temporal (341 ± 74 μm) locations. The difference in ChT between myopic and nonmyopic children was significantly greater in central foveal regions compared to more peripheral regions (>3 mm diameter, P < 0.001). CONCLUSIONS Myopic children have significantly thinner choroids compared to nonmyopic children of similar age, particularly in central foveal regions. The magnitude of difference in choroidal thickness associated with myopia appears greater than would be predicted by a simple passive choroidal thinning with axial elongation.

Assessment of corneal dynamics with high-speed swept source Optical Coherence Tomography combined with an air puff system

We present a novel method and instrument for in vivo imaging and measurement of the human corneal dynamics during an air puff. The instrument is based on high-speed swept source optical coherence tomography (ssOCT) combined with a custom adapted air puff chamber from a non-contact tonometer, which uses an air stream to deform the cornea in a non-invasive manner. During the short period of time that the deformation takes place, the ssOCT acquires multiple A-scans in time (M-scan) at the center of the air puff, allowing observation of the dynamics of the anterior and posterior corneal surfaces as well as the anterior lens surface. The dynamics of the measurement are driven by the biomechanical properties of the human eye as well as its intraocular pressure. Thus, the analysis of the M-scan may provide useful information about the biomechanical behavior of the anterior segment during the applanation caused by the air puff. An initial set of controlled clinical experiments are shown to comprehend the performance of the instrument and its potential applicability to further understand the eye biomechanics and intraocular pressure measurements. Limitations and possibilities of the new apparatus are discussed.

Predicting Dry Eye Using Noninvasive Techniques of Tear Film Surface Assessment

PURPOSE To measure tear film surface quality in healthy and dry eye subjects using three noninvasive techniques of tear film quality assessment and to establish the ability of these noninvasive techniques to predict dry eye. METHODS Thirty-four subjects participated in the study and were classified as dry eye or normal, based on standard clinical assessments. Three noninvasive techniques were applied for measurement of tear film surface quality: dynamic-area high-speed videokeratoscopy (HSV), wavefront sensing (DWS), and lateral shearing interferometry (LSI). The measurements were performed in both natural (NBC) and suppressed (SBC) blinking conditions. RESULTS To investigate the capability of each method to discriminate dry eye subjects from normal subjects, the receiver operating curve (ROC) was calculated and then the area under the curve (AUC) was extracted. The best result was obtained for the LSI technique (AUC = 0.80 in SBC and AUC = 0.73 in NBC), which was followed by HSV (AUC = 0.72 in SBC and AUC = 0.71 in NBC). The best result for DWS was an AUC of 0.64 obtained for changes in vertical coma in SBC, whereas for NBC, the results were poorer. CONCLUSIONS Noninvasive techniques of tear film surface assessment can be used for predicting dry eye, and such an assay can be achieved in NBC as well as SBC. In this study, LSI showed the best detection performance, closely followed by the dynamic-area HSV. The DWS technique was less powerful, particularly in NBC.

Tear film surface quality with soft contact lenses using dynamic-area high-speed videokeratoscopy.

Objectives To evaluate the performance of the dynamic-area high-speed videokeratoscopy technique in the assessment of tear film surface quality with and without the presence of soft contact lenses on eye. Methods Retrospective data from a tear film study (Kopf et al., J Optom. 2008;1:14–21) using basic high-speed videokeratoscopy, captured at 25 frames per sec, were used. Eleven subjects underwent tear film analysis conducted in the morning, midday, and evening on the first and seventh day of 1 week of no lens wear. Five of the 11 subjects then completed an extra week of hydrogel lens wear, followed by a week of silicone hydrogel lens wear. Analysis was performed on a 6-sec period of the interblink recording. The dynamic-area high-speed videokeratoscopy technique uses the maximum available area of Placido ring pattern reflected from the tear interface and eliminates regions of disturbance because of shadows from the eyelashes. A value of tear film surface quality was derived using image-processing techniques based on the quality of the reflected ring pattern orientation. Results The group mean tear film surface quality and the standard deviations for each of the conditions (bare eye, hydrogel lens, and silicone hydrogel lens) showed a much lower coefficient of variation than that of previous methods (average reduction of approximately 92%). Bare eye measurements from the right and left eyes of 11 individuals showed high correlation values (Pearson correlation r = 0.73, P<0.05). Repeated measures ANOVA across the 6-sec period of measurement in the normal interblink period for the bare eye condition showed no statistically significant changes. However, across the 6-sec interblink period with both the contact lenses, statistically significant changes were observed (P<0.001). Overall, wearing hydrogel and silicone hydrogel lenses caused the tear film surface quality to worsen compared with that of the bare eye condition (repeated measures ANOVA, P<0.0001 for both the hydrogel and silicone hydrogel). Conclusions The results suggest that the dynamic-area method of high-speed videokeratoscopy was able to distinguish and quantify the subtle, but systematic worsening of tear film surface quality in the interblink interval in contact lens wear. It was also able to clearly show a difference between bare eye and contact lens wearing conditions.

Longitudinal changes in choroidal thickness and eye growth in childhood.

PURPOSE To examine longitudinal changes in choroidal thickness and axial length in a population of children with a range of refractive errors. METHODS One hundred and one children (41 myopes and 60 nonmyopes) aged 10 to 15 years participated in this prospective, observational longitudinal study. For each child, 6-month measures of choroidal thickness (using enhanced depth imaging optical coherence tomography) and axial ocular biometry were collected four times over an 18-month period. Linear mixed-models were used to examine the longitudinal changes in choroidal thickness and the relationship between changes in choroidal thickness and axial eye growth over the study period. RESULTS A significant group mean increase in subfoveal choroidal thickness was observed over 18 months (mean increase 13 ± 22 μm, P < 0.001). Myopic children exhibited significantly thinner choroids compared with nonmyopic children (P < 0.001), although there was no significant time by refractive group interaction (P = 0.46), indicating similar changes in choroidal thickness over time in myopes and nonmyopes. However, a significant association between the change in choroidal thickness and the change in axial length over time was found (P < 0.001, β = -0.14). Children showing faster axial eye growth exhibited significantly less choroidal thickening over time compared with children showing slower axial eye growth. CONCLUSIONS A significant increase in choroidal thickness occurs over an 18-month period in normal 10- to 15-year-old children. Children undergoing faster axial eye growth exhibited less thickening and, in some cases, a thinning of the choroid. These findings support a potential role for the choroid in the mechanisms regulating eye growth in childhood.

Lateral shearing interferometry, dynamic wavefront sensing, and high-speed videokeratoscopy for noninvasive assessment of tear film surface characteristics: a comparative study.

There are several noninvasive techniques for assessing the kinetics of tear film, but no comparative studies have been conducted to evaluate their efficacies. Our aim is to test and compare techniques based on high-speed videokeratoscopy (HSV), dynamic wavefront sensing (DWS), and lateral shearing interferometry (LSI). Algorithms are developed to estimate the tear film build-up time T(BLD), and the average tear film surface quality in the stable phase of the interblink interval TFSQ(Av). Moderate but significant correlations are found between T(BLD) measured with LSI and DWS based on vertical coma (Pearsons r(2)=0.34, p<0.01) and higher order rms (r(2)=0.31, p<0.01), as well as between TFSQ(Av) measured with LSI and HSV (r(2)=0.35, p<0.01), and between LSI and DWS based on the rms fit error (r(2)=0.40, p<0.01). No significant correlation is found between HSV and DWS. All three techniques estimate tear film build-up time to be below 2.5 sec, and they achieve a remarkably close median value of 0.7 sec. HSV appears to be the most precise method for measuring tear film surface quality. LSI appears to be the most sensitive method for analyzing tear film build-up.

Assessment of Tear Film Surface Quality Using Dynamic-Area High-Speed Videokeratoscopy

A new method for noninvasive assessment of tear film surface quality (TFSQ) is proposed. The method is based on high-speed videokeratoscopy in which the corneal area for the analysis is dynamically estimated in a manner that removes videokeratoscopy interference from the shadows of eyelashes but not that related to the poor quality of the precorneal tear film that is of interest. The separation between the two types of seemingly similar videokeratoscopy interference is achieved by region-based classification in which the overall noise is first separated from the useful signal (unaltered videokeratoscopy pattern), followed by a dedicated interference classification algorithm that distinguishes between the two considered interferences. The proposed technique provides a much wider corneal area for the analysis of TFSQ than the previously reported techniques. A preliminary study with the proposed technique, carried out for a range of anterior eye conditions, showed an effective behavior in terms of noise to signal separation, interference classification, as well as consistent TFSQ results. Subsequently, the method proved to be able to not only discriminate between the bare eye and the lens on eye conditions but also to have the potential to discriminate between the two types of contact lenses.

Estimating Corneal Surface Topography in Videokeratoscopy in the Presence of Strong Signal Interference

Videokeratoscopy techniques rely on a number of factors in order to achieve accurate estimates of corneal surface topography. Good tear film quality, minimal reflections from eyelashes, and minimal eye movements are essential for corneal topography estimates to be reliable. However, in practice, these ideal conditions may not always be fulfilled, especially in cases of subjects diagnosed with dry eye syndrome, having narrow palpebral apertures, long eyelashes, or nystagmus (uncontrolled eye movements). Such nonoptimal conditions of image acquisition result in poorer estimates of corneal topography. The aim of this paper was to devise a technique that would provide more accurate estimation of corneal topography in such situations and particularly when the source of signal interference is strong. This was achieved by developing a set of algorithms that extract the interference from the acquired raw videokeratoscopic image and filter the topography according to the interference location. The experiments carried out with test surfaces and real corneas showed that this new technique leads to a significant improvement in the topography estimator. Additionally, it is an interference indication procedure that, in the future, could be used for the purpose of tear film quality estimation.

Morphological changes in the conjunctiva, episclera and sclera following short-term miniscleral contact lens wear in rigid lens neophytes.

PURPOSE To quantify the influence of short-term wear of miniscleral contact lenses on the morphology of the corneo-scleral limbus, the conjunctiva, episclera and sclera. METHODS OCT images of the anterior eye were captured before, immediately following 3h of wear and then 3h after removal of a miniscleral contact lens for 10 young (27 ± 5 years) healthy participants (neophyte rigid lens wearers). The region of analysis encompassed 1mm anterior, to 3.5mm posterior to the scleral spur. Natural diurnal variations in thickness were measured on a separate day and compensated for in subsequent analyses. RESULTS Following 3h of lens wear, statistically significant tissue thinning was observed across all quadrants, with a mean decrease in thickness of -24.1 ± 3.6 μm (p<0.001), which diminished, but did not return to baseline 3h after lens removal (-16.9 ± 1.9 μm, p<0.001). The largest tissue compression was observed in the superior quadrant (-49.9 ± 8.5 μm, p<0.01) and in the annular zone 1.5mm from the scleral spur (-48.2 ± 5.7 μm), corresponding to the approximate edge of the lens landing zone. Compression of the conjunctiva/episclera accounted for about 70% of the changes. CONCLUSIONS Optimal fitting miniscleral contact lenses worn for three hours resulted in significant tissue compression in young healthy eyes, with the greatest thinning observed superiorly, potentially due to the additional force of the eyelid, with a partial recovery of compression 3h after lens removal. Most of the morphological changes occur in the conjunctiva/episclera layers.