Superior Meridians Research Articles

Relationship between Choroidal Thickness and Anterior Scleral Thickness in Patients with Keratoconus.

To evaluate the relationship between choroidal thickness (CT) and anterior scleral thickness (AST) in patients with subclinical keratoconus (SKC) and established keratoconus (KC). This single-center prospective case-control study included 97 eyes of 97 patients: 44 KC eyes, 14 SKC eyes, and 39 age- and axial length (AL)-matched healthy eyes. Using swept-source optical coherence tomography, the AST was manually measured in four directions and the CT was obtained automatically from the Early Treatment Diabetic Retinopathy Study (ETDRS) grid. Principal component analysis (PCA) was used to linearly reduce the dimensionality of nine CT inputs to one significant component, CT1. A multivariate model was created to evaluate the association between CT1, AST, and several ocular parameters in SKC and KC patients. Partial correlation was then performed to adjust the confounding factors and to examine the effect of AST on CT1. The PCA showed that CT1 accounts for 86.54% of the total variance in the nine original CTs of the ETDRS grid. The CT1 model was associated with age, AL, and AST in the superior meridian in SKC eyes, whereas in KC eyes, it was correlated with gender, age, AL, and AST in the inferior meridian (p < 0.001). The partial correlation between CT1 and AST in the superior zone was found to be significant, positive, and strong in SKC eyes (r = 0.79, p = 0.019), whereas a significant, positive, and moderate correlation between CT1 and AST at the inferior zone (r = 0.41, p = 0.017) was observed in KC eyes. Choroidal tissue was significantly correlated with the anterior sclera across the vertical meridian. This relationship was observed over the superior sclera in SKC eyes, whereas in established KC, it was over the inferior sclera. These results reveal new insights regarding the interactions between the anterior and posterior structures of the KC eyes and confirm the enigma of the pathophysiology of KC.

Performance of neuroretinal rim thickness measurement by Cirrus high-definition optical coherence tomography in myopic eyes

Neuroretinal rim (NRR) measurement can aid the diagnosis of glaucoma. A few studies reported that Cirrus optical coherence tomography (OCT) had NRR segmentation errors. The current study investigated segmentation success of NRR in myopic eyes using the Cirrus built-in software and to determine the number of acquisitions required to identify NRR thinning. Right eye of 87 healthy adult myopes had an optic disc scanned using Cirrus HD-OCT for five successive acquisitions. A masked examiner evaluated 36 radial line images of each scan to screen for segmentation errors using the built-in software at the Bruch’s membrane opening (BMO) and/or internal limiting membrane (ILM). Participants with three accurate NRR acquisitions had their average NRR thickness determined. This result was compared with average of the two acquisitions and the first acquisition. Among 435 OCT scans of the optic disc (87 eyes × 5 acquisitions), 129 (29.7%) scans had segmentation errors that occurred mainly at the ILM. The inferior-temporal and superior meridians had slightly more segmentation errors than other meridians, independent of axial length, amount of myopia, or presence of peripapillary atrophy. Sixty-five eyes (74.7%) had at least three accurate NRR measurements. The three acquisitions had high reliability in NRR thickness in the four quadrants (intraclass correlation coefficient > 0.990, coefficient of variation < 3.9%). NRR difference between the first acquisition and the average of three acquisitions was small (mean difference 2 ± 13 μm, 95% limits of agreement within ± 30 μm) among the four quadrants. Segmentation errors in NRR measurements appeared regardless of axial length, amount of myopia, or presence of peripapillary atrophy. Cirrus segmentation lines should be manually inspected when measuring NRR thickness.

Two-port dry vitrectomy for rhegmatogenous retinal detachment: a pilot study.

To evaluate the safety and efficacy of a new surgical technique for the management of primary rhegmatogenous retinal detachment (RRD), consisting of localized PPV near the retinal break(s), without infusion line, associated with a drainage of subretinal fluid and cryoretinopexy. Multicentric prospective study conducted at the University Hospital of Cagliari and IRCCS Fondazione Policlinico Universitario A. Gemelli, Roma. Twenty eyes affected by RRD with the causative retinal break(s) in the superior meridians were enrolled between February 2022 and June 2022. Patients with cataract ≥3, aphakia, significant posterior capsule opacification, giant retinal tears, retinal dialysis, history of trauma and PVR ≥C2 were excluded. All eyes underwent a two-port 25-gauge PPV with localized removal of the vitreous surrounding retinal break(s), followed by 20% SF6 injection and cryopexy. The surgical time was recorded for each procedure. Best-corrected visual acuity (BCVA) was measured at baseline and postoperative 6 months. Primary anatomic success at 6 months was achieved by 85% of patients. No complications occurred, except for three (15%) retinal re-detachments. The average surgical time was 8.61 ± 2.16 min. Overall, the difference between pre- and last postoperative mean BCVA was statistically significant (p = 0.02). Two-port dry PPV demonstrated safety and efficacy for the treatment of RRD, reaching an 85% of anatomical success rate. Although further studies are necessary to confirm the efficacy and long-term benefit of this treatment, we believe that this surgical technique could be considered a valid and safe alternative for the management of primary RRD.

The link between anterior scleral thickness, corneal biomechanical response and ocular parameters

AbstractPurpose: to assess anterior scleral thickness (AST) across diverse scleral meridians and to evaluate the relationship with corneal biomechanical response and several ocular parameters.Methods: This prospective non‐randomized study comprised 50 eyes of 50 patients (mean age, 29.02 ± 9.48 years). Anterior scleral thickness was measured meridionally at three scleral locations (1‐, 2‐, and 3‐mm posterior to the scleral spur) using swept‐source optical coherence tomography. A multivariate model was created to associate AST with several ocular parameters. Principal component analysis (PCA) was used to reduce linearly the dimensionality of seven biomechanical input metrics to two significant components, C1 and C2. Two multivariate analyses were performed to associate C1 and C2 with AST and ocular parameters.Results: AST was thickest in the inferior (581 ± 52 μm) and thinnest in the superior meridian (441 ± 42 μm) when compared to all meridians (p &lt; 0.001), and similar in the nasal (529 ± 53 μm) and temporal (511 ± 59 μm) meridians (p &gt; 0.05). The sclera exhibited the thinnest point 2 mm posterior to the scleral spur (p &lt; 0.001). The AST was significantly linked with axial length, central corneal thickness, and intraocular pressure (p &lt; 0.001). The PCA showed that C1 accounts for 53.84% whereas C2 for the 16.51% of the total variance in the original variables. The C1 model was significantly associated with AST along all meridians (p &lt; 0.001). The partial correlation was moderate in the nasal (r = −0.36, p &lt; 0.001) and inferior (r = −0.26, p = 0.004) meridians whereas weak in the temporal (r = −0.14, p = 0.05) and superior (r = −0.15, p = 0.05) meridians.Conclusions: The relationship between the new biomechanical component and the AST provides the first evidence of the association of AST with the corneal response parameters which should be considered in corneal response interpretation. Tissue thickness varied significantly among meridians supporting the asymmetrical expansion of the ocular globe. The AST was associated with several ocular parameters.

Анализ результатов пневморетинопексии при хирургическом лечении регматогенной отслойки сетчатки

Introduction. Pneumoretinopexy is low-traumatic and minimally invasive technique for treatment retinal detachment. Purpose. Analysis clinical efficacy of pneumoretinopexy in treatment rhegmatogenous retinal detachment. Material and methods. 9 patients (9 eyes) aged 35 to 67 years (all women) were selected. Selection criteria: rhegmatogenous retinal detachment, the presence of one or two horseshoe retinal tear in the superior meridians. Results. On 3–5th days, all 9 patients had blockage of retinal tear, in 4 eyes the height of the retinal detached significantly decreased, in 5 patients had complete reattachment of the retina. Barrier laser retinal photocoagulation of the areas of retinal tears was performed, a barrier of coagulates was formed around the blocked tears. Patients were discharged on the 7 th day. Recurrent retinal detachment occurred in 2 patients (2 eyes). At the end of the follow-up period, after complete gas resorption in the vitreous chamber, visual acuity in all patients increased above 0.1, on average – 0.3. Conclusion. Pneumoretinopexy is effective in recent cases of rhegmatogenous retinal detachment with follow-up periods of up to 1 month. Pneumoretinopexy should be used with caution in eyes with pseudophakia; on the eyes with large retinal tears in the meridian below 1–11 o'clock meridians. Keywords: pneumoretinopexy, retinal detachment, recurrent retinal detachment, surgical treatment of retinal detachment.

The Link between Anterior Scleral Thickness, Corneal Biomechanical Response, and Ocular Parameters

Introduction: This study aimed to assess anterior scleral thickness (AST) across diverse scleral meridians and to evaluate the relationship with corneal biomechanical response and several ocular parameters. Methods: This prospective nonrandomized study comprised 50 eyes of 50 patients (mean age, 29.02 ± 9.48 years). AST was measured meridionally at three scleral locations (1, 2, and 3 mm posterior to the scleral spur) using swept-source optical coherence tomography. A multivariate model was created to associate AST with several ocular parameters. Principal component analysis (PCA) was used to reduce linearly the dimensionality of seven biomechanical input metrics to two significant components, C1 and C2. Two multivariate analyses were performed to associate C1 and C2 with AST and ocular parameters. Results: AST was thickest in the inferior (581 ± 52 µm) and thinnest in the superior meridian (441 ± 42 µm) when compared to all meridians (p < 0.001) and similar in the nasal (529 ± 53 µm) and temporal (511 ± 59 µm) meridians (p > 0.05). The sclera exhibited the thinnest point 2 mm posterior to the scleral spur (p < 0.001). The AST was significantly linked with axial length, central corneal thickness, and intraocular pressure (p < 0.001). The PCA showed that C1 accounts for 53.84%, whereas C2 for the 16.51% of the total variance in the original variables. The C1 model was significantly associated with AST along all meridians (p < 0.001). The partial correlation was moderate in the nasal (r = −0.36, p < 0.001) and inferior (r = −0.26, p = 0.004) meridians, whereas weak in the temporal (r = −0.14, p = 0.05) and superior (r = −0.15, p = 0.05) meridians. Conclusions: The relationship between the new biomechanical component and the AST provides the first evidence of the association of AST with the corneal response parameters which should be considered in corneal response interpretation. Tissue thickness varied significantly among meridians supporting the asymmetrical expansion of the ocular globe. The AST was associated with several ocular parameters.

Three-dimensional composition of the photoreceptor cone layers in healthy eyes using adaptive-optics optical coherence tomography (AO-OCT).

To assess the signal composition of cone photoreceptors three-dimensionally in healthy retinas using adaptive optics optical coherence tomography (AO-OCT). Study population. Twenty healthy eyes of ten subjects (age 23 to 67). Procedures. After routine ophthalmological assessments, eyes were examined using AO-OCT. Three-dimensional volumes were acquired at 2.5° and 6.5° foveal eccentricity in four main meridians (superior, nasal, inferior, temporal). Cone densities and signal compositions were investigated in four different planes: the cone inner segment outer segment junction (IS/OS), the cone outer segment combined with the IS/OS (ISOS+), the cone outer segment tips (COST) and full en-face plane (FEF) combining signals from all mentioned cone layers. Additionally, reliability of a simple semi-automated approach for assessment of cone density was tested. Main outcome measures. Cone density of IS/OS, IS/OS+, COST and FEF. Qualitative depiction and composition of each cone layer. Inter-rater agreement of cone density measurements. Mean overall cone density at all eccentricities was highest at the FEF plane (21.160/mm2), followed by COST (20.450/mm2), IS/OS+ (19.920/mm2) and IS/OS (19.530/mm2). The different meridians and eccentricities had a significant impact on cone density, with lower eccentricity resulting in higher cone densities (p≤.001), which were highest at the nasal, then temporal, then inferior and then superior meridian. Depiction of the cone mosaic differed between all 4 layers regarding signal size and packing density. Therefore, different cone layers showed evident but not complete signal overlap. Using the semi-automated technique for counting of cone signals achieved high inter-rater reliability (ICC > .99). In healthy individuals qualitative and quantitative changes in cone signals are found not only in different eccentricities and meridians, but also within different photoreceptor layers. The variation between cone planes has to be considered when assessing the integrity of cone photoreceptors in healthy and diseased eyes using adaptive optics technology.

Three-dimensional assessment of para- and perifoveal photoreceptor densities and the impact of meridians and age in healthy eyes with adaptive-optics optical coherence tomography (AO-OCT).

An adaptive optics optical coherence tomography (AO-OCT) system is used to assess sixty healthy eyes of thirty subjects (age 22 to 75) to evaluate how the outer retinal layers, foveal eccentricity and age effect the mean cone density. The cone mosaics of different retinal planes (the cone inner segment outer segment junction (IS/OS), the cone outer segment combined with the IS/OS (ISOS+), the cone outer segment tips (COST), and the full en-face plane (FEF)) at four main meridians (superior, nasal, inferior, temporal) and para- and perifoveal eccentricities (ecc 2.5° and 6.5°) were analyzed quantitatively. The mean overall cone density was 19,892/mm2 at ecc 2.5° and 13,323/mm2 at ecc 6.5°. A significant impact on cone density was found for eccentricity (up to 6,700/mm2 between ecc 2.5° and 6.5°), meridian (up to 3,700/mm2 between nasal and superior meridian) and layer (up to 1,400/mm2 between FEF and IS/OS). Age showed only a weak negative effect. These factors as well as inter-individual variability have to be taken into account when comparing cone density measurements between healthy and pathologically changed eyes, as their combined effect on density can easily exceed several thousand cones per mm2 even in parafoveal regions.

Asymmetric Foveated Just-Noticeable-Difference Model for Images With Visual Field Inhomogeneities

Just noticeable difference (JND) models reveal visibility limitation of human visual system (HVS) and exploit perceptual redundancy in the visual signal. Conventional just noticeable difference (JND) model supposes the visual acuity is homogeneous with or without considerations on the isoeccentric locations. Recent research on vision science indicates that the effect of eccentricity on visual sensitivity is not homogeneous across the visual field (VF). Relevant studies have found visual acuity at the isoeccentric locations is better along the horizontal meridian than along the vertical meridian, i.e., horizontal-vertical anisotropy (HVA). Along the vertical meridian, better performance has been reported for the inferior meridian compared to the superior meridian, i.e., vertical-meridian asymmetry (VMA). These properties of HVS should be taken into account to yield a better JND estimation, for better exploiting the perceptual redundancy. In this paper, we use two hemi-ellipses to represent the iso-acuity contour, which can better express the HVA and VMA effects. Moreover, we design psychophysical experiments under different test conditions, where the results show the hemi-ellipse model performs better when compared to the circular model. Finally, we build an asymmetric foveated JND model using two hemi-ellipses for approximation. When comparing with traditional JND models, experimental results demonstrate the effectiveness of the proposed model.

The organization of the cone photoreceptor mosaic measured in the living human retina

The cone photoreceptors represent the initial fundamental sampling step in the acquisition of visual information. While recent advances in adaptive optics have provided increasingly precise estimates of the packing density and spacing of the cone photoreceptors in the living human retina, little is known about the local cone geometric arrangement beyond a tendency towards hexagonal packing. We analyzed the cone mosaic in data from 10 normal subjects. A technique was applied to calculate the local average cone mosaic structure which allowed us to determine the hexagonality, spacing and orientation of local regions. Using cone spacing estimates, we find the expected decrease in cone density with retinal eccentricity and higher densities along the horizontal as opposed to the vertical meridians. Orientation analysis reveals an asymmetry in the local cone spacing of the hexagonal packing, with cones having a larger local spacing along the horizontal direction. This horizontal/vertical asymmetry is altered at eccentricities larger than 2 degrees in the superior meridian and 2.5 degrees in the inferior meridian. Analysis of hexagon orientations in the central 1.4° of the retina shows a tendency for orientation to be locally coherent, with orientation patches consisting of between 35 and 240 cones.

Individual Variations in Human Cone Photoreceptor Packing Density: Variations with Refractive Error

To measure the variation in human cone photoreceptor packing density across the retina, both within an individual and between individuals with different refractive errors. A high-resolution adaptive optics scanning laser ophthalmoscope was used to image the cones of 11 human eyes. Five subjects with emmetropia and six subjects with myopia were tested (+0.50 to -7.50 D). For each subject, four approximately 10 degrees x 1.5 degrees strips of cone images were obtained. Each strip started at the fovea and proceeded toward the periphery along the four primary meridians. The position of each cone within the sampling windows was digitized manually by the investigator. From these cone counts, the density of the cones was calculated for a set of fixed distances from the fovea at locations throughout the image. Cone photoreceptor packing density decreased from 27,712 cells/mm(2) to 7,070 cells/mm(2) from a retinal eccentricity of 0.30 to 3.40 mm along the superior meridian in five emmetropic eyes. Cone photoreceptor packing density (cells per square millimeter) was significantly lower in myopic eyes than in emmetropic eyes. At a given location, there was considerable individual variation in cone photoreceptor packing density, although more than 20% of the variance could be accounted for by differences in axial length. The results provide a baseline analysis of individual difference in cone photoreceptor packing density in healthy human eyes. As predicted by retinal stretching models, cone photoreceptor packing density is lower in highly myopic eyes than in emmetropic eyes.

Comparison of Single-Segment and Double-Segment Intacs for Keratoconus and Post-LASIK Ectasia

To evaluate the efficacy of single-segment Intacs and compare with double-segment Intacs in subjects with post-LASIK ectasia and keratoconus. Retrospective comparative analysis. setting: Boxer Wachler Vision Institute, Beverly Hills, California, USA. study population: Thirty-seven eyes of 28 patients with keratoconus and post-LASIK ectasia classified into two groups: single-segment group (17 eyes, 11 patients) and double-segment group (20 eyes, 17 patients). Both groups were matched for age, visual acuity (uncorrected, UCVA; best spectacle-corrected, BSCVA), refractive error (sphere, cylinder, spherical equivalent), and keratometry (K) value (flat, steep, average) by t test for equality of means. intervention: Single- or double-segment Intacs procedure with axis of incision for insertion in the steep axis of manifest refraction. main outcome measure: Improvement of acuity, refractive error, K values, and inferior-superior (I-S) ratio. There was more improvement in UCVA in the single-segment group (nine lines) than the double-segment group (2.5 lines), P < .01; in BSCVA in the single-segment group (2.5 lines) than the double-segment group (<1 line), P < .01; in steep K values in the single-segment group (2.76 diopters +/- 2.68) than the double-segment group (0.93 diopters +/- 2.01), P = .02; and in I-S ratio in the single-segment group (9.51 +/- 7.49) than the double-segment group (4.22 +/- 4.82), P = .01; and greater cylinder decrease after Holladay vector analysis in the single-segment group (5.69 diopters +/- 3.10) than the double-segment group (1.58 diopters +/- 3.09), P < .01. Single-segment Intacs improved both UCVA and BSCVA by differential flattening of inferior meridian and steepening of superior meridian as reflected by change in I-S ratio.

Iridolenticular contact decreases following laser iridotomy for pigment dispersion syndrome.

To evaluate changes in anterior segment anatomy after laser iridotomy for pigment dispersion syndrome. Ultrasound biomicroscopy was performed on 7 eyes of 7 untreated patients with reverse pupillary block and pigment dispersion syndrome. A radially oriented image with the probe perpendicular to the eye in the superior meridian was obtained before and at least 1 week after laser iridotomy in each eye. We assessed changes in angle recess area and iris-lens contact distance. Mean +/- SD patient age was 31.3 +/- 5.7 years and mean +/- SD refractive error was -5.0 +/- 3.9 diopters. Angle recess area (mean +/- SD, 0.78 +/- 0.28 vs 0.35 +/- 0.11 mm2; P=.001, paired t test) and iris-lens contact distance (2.05 +/- 0.28 vs 0.79 +/- 0.13 mm; P<.001) decreased following iridotomy. Central anterior chamber depth did not change. Flattening of the iris following laser iridotomy for pigment dispersion syndrome causes a decrease in iris-lens contact and angle width while lens position remains constant.

Evaluating the Visual Field Effects of Blepharoptosis Using Automated Static Perimetry

Quantitation of the effects of blepharoptosis on the visual field has largely been limited to manual kinetic perimetry using a single peripheral isopter. The authors evaluated the visual dysfunction caused by blepharoptosis using automated static full-threshold perimetry. A custom static full-threshold 60 degrees test strategy on the Humphrey field analyzer was used to assess the visual fields of 20 volunteers at their normal baseline and after inducing mild and moderately severe blepharoptosis by applying gold weights to the eyelids. Threshold sensitivities were measured at points along the eight principal meridians, separated by 45 degrees, traditionally used to assess visual field impairment. For mild blepharoptosis, essentially all test points along the superior meridian were significantly depressed (P < 0.01), with an increase in slope secondary to greater decreases in sensitivity at more eccentric points. For moderately severe blepharoptosis, depression of the superior meridian was expectedly greater than that seen with mild blepharoptosis. Additionally, depression of the horizontal meridians and to a lesser extent the lower meridians also was noted. These results suggest that even mild blepharoptosis may be associated with depression of the superior visual field extending close to fixation. Ophthalmologists should be aware of the effect of blepharoptosis when testing for other ophthalmic or neurologic disorders using automated static perimetry. Full-threshold static perimetry can be used to quantitate the visual field loss associated with blepharoptosis as a means of evaluating visual impairment.

Pars plana and ora serrata anatomotopographic study of fetal eyes.

Morphology and topographic anatomical relations of pars plana, pars plicata and ora serrata were examined in 15 globes of fetuses, obtained from autopsy. The mean value of pars plana size was: nasal meridian = 1.15 +/- 0.32 mm; temporal meridian = 1.20 +/- 0.34 mm; superior meridian = 1.19 +/- 0.34 mm; inferior meridian = 1.15 +/- 0.34 mm. The mean value of the distance between the sclerocorneal limbus and the ora serrata was: nasal meridian = 3.22 +/- 0.30 mm; temporal meridian = 3.33 +/- 0.35 mm; superior meridian = 3.23 +/- 0.36 mm; and inferior meridian = 3.27 +/- 0.37 mm. A significant difference between the mean sizes of the pars plana in the superior meridian was found compared to the nasal and inferior meridian. The distances from Schwalbe's line to the ora serrata in the 4 meridians did not vary significantly. A positive, significant correlation between the antero-posterior diameter and the distances from the sclerocorneal limbus to the ora serrata was demonstrated in the 4 meridians.

On the lunar atmospheric tide at St. Helena

The results of the observations made by Captain Lefroy, of the Royal Artillery, Director of the Magnetical and Meteorological Ob­servatory at St. Helena, are here given; from which it appears, on the examination of the barometrical changes during seventeen months, that a maximum of pressure corresponds to the moon’s passage over both the inferior and superior meridians, being slightly greater in the latter case, and that a minimum corresponds nearly to the rising and setting, or to six hours before and after the former periods. The average atmospheric pressures are 28·2714 inches in the first case, and 28·2675 in the last; the difference being 0'0039 inch. The height of the cistern of the barometer above the sea is 1764 feet; and the latitude of the Observatory 15° 57' S. These results were still further confirmed by those of a series of observations during two years. These observations also establish the conclusion that the moon exerts a greater influence on the amount of atmospheric pressure at the periods of her perigee than at those of her apogee.

On the influence of the moon on the atmospheric pressure, as deduced from the observations of the barometer made at the magnetic observatory at St. Helena

In order to determine the dependence of the barometric pressure on lunar influence, the author arranges all the two-hourly observations in each lunar month with relation to the time of the moon's passing the meridian; entering in one column the observation of each day nearest to the meridian passage, whether before or after; and entering in separate columns those corresponding to two hours, four hours, six hours, &amp;c., before and also after that observation. The monthly means at every two hours from the meridian passage are then taken; and again, the means at the same intervals, for each three months from September 1840 to December 1841. From the results thus obtained the author states that it appears that the moon's passage over both the inferior and superior meridian produces a slight increase of pressure; a maximum in the curve occurring at both (that of the latter being slightly the greater), while the minima correspond to the moon's rising or setting. It appears also, that the rise of the tides will not account for the whole amount of the increase of pressure, even admitting that it has a tendency to produce an effect of that nature. The times of maxima do not correspond; and there appears to be no atmospheric establishment. The pressure is greater about the period of new moon than at full moon; and greater in the third and fourth than in the first and second quarters; a result which agrees with that given by Mr. Howard for the climate of London. The observations of both years agree in making the pressure greater under the Perigee than under the Apogee. Mr. Howard had found that the mean pressure in Great Britain, which is in the opposite hemisphere from St. Helena, is greater under the Apogee than under the Perigee.