Blind spot size depends on the optic disc topography: a study using SLO controlled scotometry and the Heidelberg retina tomograph

Fine-scale measurement of the blind spot borders

The blind spot is both a necessity and a nuisance for seeing. It is the portion of the visual field projecting to where the optic nerve crosses the retina, a region devoid of photoreceptors and hence visual input. The precise way in which vision transitions into blindness at the blind spot border is to date unknown. A chief challenge to map this transition is the incessant movement of the eye, which unavoidably smears measurements across space. In this study, we used high-resolution eye-tracking and state-of-the-art retinal stabilization to finely map the blind spot borders. Participants reported the onset of tiny high-contrast probes that were briefly flashed at precise positions around the blind spot. This method has sufficient resolution to enable mapping of blood vessels from psychophysical measurements. Our data show that, even after accounting for eye movements, the transition zones at the edges of the blind spot are considerable. On the horizontal meridian, the regions with detection rates between 80% and 20% span approximately 25% of the overall width of the blind spot. These borders also vary considerably in size across different axes. These data show that the transition from full visibility to blindness at the blind spot border is not abrupt but occurs over a broad area.

Myopia: Histology, clinical features, and potential implications for the etiology of axial elongation

Myopic axial elongation is associated with various non-pathological changes. These include a decrease in photoreceptor cell and retinal pigment epithelium (RPE) cell density and retinal layer thickness, mainly in the retro-equatorial to equatorial regions; choroidal and scleral thinning pronounced at the posterior pole and least marked at the ora serrata; and a shift in Bruch's membrane opening (BMO) occurring in moderately myopic eyes and typically in the temporal/inferior direction. The BMO shift leads to an overhang of Bruch's membrane (BM) into the nasal intrapapillary compartment and BM absence in the temporal region (i.e., parapapillary gamma zone), optic disc ovalization due to shortening of the ophthalmoscopically visible horizontal disc diameter, fovea-optic disc distance elongation, reduction in angle kappa, and straightening/stretching of the papillomacular retinal blood vessels and retinal nerve fibers. Highly myopic eyes additionally show an enlargement of all layers of the optic nerve canal, elongation and thinning of the lamina cribrosa, peripapillary scleral flange (i.e., parapapillary delta zone) and peripapillary choroidal border tissue, and development of circular parapapillary beta, gamma, and delta zone. Pathological features of high myopia include development of macular linear RPE defects (lacquer cracks), which widen to round RPE defects (patchy atrophies) with central BM defects, macular neovascularization, myopic macular retinoschisis, and glaucomatous/glaucoma-like and non-glaucomatous optic neuropathy. BM thickness is unrelated to axial length. Including the change in eye shape from a sphere in emmetropia to a prolate (rotational) ellipsoid in myopia, the features may be explained by a primary BM enlargement in the retro-equatorial/equatorial region leading to axial elongation.

Microvascular Alterations of Peripapillary Choriocapillaris in Young Adult High Myopia Detected by Optical Coherence Tomography Angiography

(1) Background: The microstructural alterations of the peripapillary choriocapillaris in high myopes remain elusive. Here, we used optical coherence tomography angiography (OCTA) to explore factors involved in these alterations. (2) Methods: This cross-sectional control study included 205 young adults' eyes (95 with high myopia and 110 with mild to moderate myopia). The choroidal vascular network was imaged using OCTA, and the images underwent manual adjustments to determine the peripapillary atrophy (PPA)-β zone and microvascular dropout (MvD). The area of MvD and the PPA-β zone, spherical equivalent (SE), and axial length (AL) were collected and compared across groups. (3) Results: The MvD was identified in 195 eyes (95.1%). Highly myopic eyes exhibited a significantly greater area for the PPA-β zone (1.221 ± 0.073 vs. 0.562 ± 0.383 mm², p = 0.001) and MvD (0.248 ± 0.191 vs. 0.089 ± 0.082 mm², p < 0.001) compared with mildly to moderately myopic eyes, and a lower average density in the choriocapillaris. Linear regression analysis showed that the MvD area correlated with age, SE, AL, and the PPA-β area (all p < 0.05). (4) Conclusions: This study found that MvDs represent choroidal microvascular alterations in young-adult high myopes, which were correlated with age, SE, AL, and the PPA-β zone. In this disorder, OCTA is important for characterizing the underlying pathophysiological adaptations.

[The history and prospects of the microperimetry method in diagnosis of pathologies of the macular region and the optic nerve]

The article discusses the historical development stages of diagnostics of the functional state of the retina and the optic nerve using microperimetry in the Russian Federation and other countries, as well as the features and diagnostic prospects of the microperimetry method in identifying fundus pathologies.

Optic nerve head anatomy in myopia and glaucoma, including parapapillary zones alpha, beta, gamma and delta: Histology and clinical features

The optic nerve head can morphologically be differentiated into the optic disc with the lamina cribrosa as its basis, and the parapapillary region with zones alpha (irregular pigmentation due to irregularities of the retinal pigment epithelium (RPE) and peripheral location), beta zone (complete RPE loss while Bruch's membrane (BM) is present), gamma zone (absence of BM), and delta zone (elongated and thinned peripapillary scleral flange) within gamma zone and located at the peripapillary ring. Alpha zone is present in almost all eyes. Beta zone is associated with glaucoma and may develop due to a IOP rise-dependent parapapillary up-piling of RPE. Gamma zone may develop due to a shift of the non-enlarged BM opening (BMO) in moderate myopia, while in highly myopic eyes, the BMO enlarges and a circular gamma zone and delta zone develop. The ophthalmoscopic shape and size of the optic disc is markedly influenced by a myopic shift of BMO, usually into the temporal direction, leading to a BM overhanging into the intrapapillary compartment at the nasal disc border, a secondary lack of BM in the temporal parapapillary region (leading to gamma zone in non-highly myopic eyes), and an ocular optic nerve canal running obliquely from centrally posteriorly to nasally anteriorly. In highly myopic eyes (cut-off for high myopia at approximately -8 diopters or an axial length of 26.5 mm), the optic disc area enlarges, the lamina cribrosa thus enlarges in area and decreases in thickness, and the BMO increases, leading to a circular gamma zone and delta zone in highly myopic eyes.

Optoelectrophysiological stimulation of the human eye using fundus-controlled silent substitution technique

We design, characterize, and apply a novel optoelectrophysiological setup for a fundus-controlled silent substitution technique that accounts for interindividual variability in retina morphology and simultaneously monitors the stimulation site under investigation. We connect a digital color liquid crystal on silicon projector, an electron-multiplying imager, and a light-emitting diode to a fundus camera. The temporal and spatial characterization reveal a maximal contrast loss of 7% for the highest stimulation frequency (30 Hz) and maximum cutoff spatial frequencies of ∼120 cycles∕deg. Two silent substitution flash sequences are applied to modulate selective activity in the short-wavelength-sensitive cone (S-cone) and combined long- and middle-wavelength-sensitive cone (LM-cone) pathways. Simultaneously, the visual evoked potentials are recorded. The data are compared to the grand average responses from a previous study that employed standard computer-screen presentation and showed very good latency matches. All the volunteers in the present examination exhibit differences between the S-cone and LM-cone evoked potentials (parameters mean values: peak-to-peak amplitude, N1 latency, and P1 latency for S-cone∕LM-cone responses: 8 μV∕15 μV, 113 ms∕89 ms, 170 ms∕143 ms). We demonstrate that the developed optoelectrophysiological setup simultaneously provides imaging, functional stimulation, and electrophysiological investigation of the retina.

Differences in parapapillary atrophy between glaucomatous and normal eyes: the Beijing Eye Study

PURPOSE

To determine in a population-based study whether parapapillary atrophy is associated with glaucoma.

DESIGN

Population-based cross-sectional study.

METHODS

The Beijing Eye Study included 4,439 of 5,324 subjects invited to participate (response rate, 83.4%). Mean age was 56.2 +/- 10.6 years (range, 40 to 101 years). Color optic disk photographs (30 degrees) were examined morphometrically. Parapapillary atrophy was divided into alpha and beta zones. Glaucomatous optic nerve atrophy was defined by a glaucomatous optic nerve head appearance.

RESULTS

After excluding highly myopic eyes, data from 4,003 (90.2%) subjects entered the statistical analysis. Glaucomatous optic nerve damage was detected in 93 (2.3%) subjects. The beta zone of parapapillary atrophy as a whole and measured separately in four disk sectors was significantly larger and occurred significantly more frequently in the glaucomatous group than in the nonglaucomatous group (beta zone total area, 1.21 +/- 1.92 mm2 vs 0.32 +/- 0.99 mm2; P < .001). In multiple regression analysis, area of beta zone was significantly associated with age (P < .001), myopic refractive error (P < .001), and presence of glaucomatous optic nerve damage (P < .001), with no significant difference between chronic open-angle glaucoma (n = 72) and chronic angle-closure glaucoma (n = 21; beta zone area, 1.20 +/- 0.39 mm2 vs 1.19 +/- 0.46 mm2; P = .69).

CONCLUSIONS

In a population-based setting, the beta zone of parapapillary atrophy is significantly larger and occurs more frequently in glaucomatous eyes than in normal eyes of Chinese adults, with no marked difference between chronic open-angle glaucoma and primary angle-closure glaucoma.

Peripapillary atrophy in elderly Chinese in rural and urban Beijing

PURPOSE

To determine peripapillary atrophy in elderly Chinese in an urban and rural regions of Beijing.

METHODS

The Beijing Eye Study a population-based, cross-sectional cohort study, included 4,439 subjects out of 5,324 subjects who were asked to participate (response rate 83.4%). Mean age was 56.2+/-10.6 years (range, 40-101 years). Colour optic disc photographs (30 degrees ) were morphometrically examined. Peripapillary atrophy was divided into alpha zone and beta zone.

RESULTS

Optic disc photographs were available for 4,027 (90.7%) subjects. Alpha zone and beta zone, respectively, were present in 2,867 (71.2%) subjects and 802 (19.9%) subjects, respectively, measuring 0.52+/-0.64 mm(2) and measuring 0.46+/-1.82 mm(2). Both zones were significantly widest and found significantly (P<0.001) most often in the temporal peripapillary region, followed by the temporal inferior region, the temporal superior region, and finally the nasal region. Size of both zones was significantly correlated with optic disc size (P<0.001), age (P<0.001), and myopic refractive error (P<0.001). Both zones increased significantly with decreasing uncorrected visual acuity (P<0.001) and decreasing best-corrected visual acuity (P<0.001). They did not vary significantly (P=0.10; and P=0.78) between male and female subjects. In multivariate analysis, the relationships between both zones and age, myopic refractive error, disc size, and uncorrected and best-corrected visual acuity remained statistically significant (P<0.001).

CONCLUSIONS

Alpha zone and beta zone of peripapillary atrophy, respectively, occur in about 70 and 20%, respectively, of elderly Chinese. As peripapillary atrophy changes in glaucomatous optic neuropathy, these normative data may be helpful for glaucoma detection.

Scotoma mapping by semi-automated kinetic perimetry: the effects of stimulus properties and the speed of subjects' responses

PURPOSE

The study aimed firstly to determine the effects of stimulus variables on the detection of a scotoma border and, secondly, to study the reproducibility of the method during semi-automated kinetic perimetry.

METHODS

The size of the physiological blind spot in 18 young normal subjects was measured with a video-campimetric device, the Tübingen computer campimeter (TCC). Kinetic stimuli of two different sizes and at four different levels of luminance were presented. Examinations were repeated within 2 weeks. Measurements were corrected for individual response times and the area of the blind spot was computed. The effects of stimulus strength and size and the repeatability of blind spot measurements were evaluated by an analysis of variance.

RESULTS

The physiological blind spot showed significant inter- and intraindividual variations in size (least square means ranging from 17 to 49 square degrees), with a standard deviation of 6.8 square degrees. The measured size of the blind spot increased as a function of decreasing stimulus value, by reducing either the relative brightness or the size of stimuli. Use of a correction for each subject's speed of responses nearly halved the level of random variance. The temporal sequence of measurements (the order in which they were performed) had no apparent effect on the calculated values of blind spot size.

CONCLUSIONS

Semi-automated kinetic perimetry can determine the size of the physiological blind spot with good repeatability in young, normal subjects. Determination of each individual's speed of response and inclusion of this variable in the calculations reduced variance of the measure significantly. This study confirmed the presence of considerable interindividual differences in the size of the physiological blind spot.

Clinical implications of peripapillary atrophy in glaucoma

PURPOSE OF REVIEW

To elucidate peripapillary atrophy in glaucomatous optic neuropathy; its ranking in the morphologic diagnosis of the glaucoma, and its value for the differentiation of various types of chronic open-angle glaucoma, for the separation of glaucomatous eyes from nonglaucomatous eyes, and for the detection of progression of glaucoma.

RECENT FINDINGS

Recent studies showed an association of peripapillary atrophy with glaucoma and the eventual development of glaucomatous disc hemorrhages independent of a small neuroretinal rim area, and an association between increasing peripapillary atrophy and progressive glaucoma. A ranking of optic disc parameters to detect glaucomatous damage revealed that the alpha and beta zones of peripapillary atrophy, compared with neuroretinal rim parameters, are less useful. Pseudoexfoliation syndrome without glaucoma is not a risk factor for peripapillary atrophy. In arteritic anterior ischemic optic neuropathy, peripapillary atrophy does not enlarge. Peripapillary atrophy does not differ markedly between Europeans and South Indians. In contrast to the position of the central retinal vessel trunk, the presence and position of cilioretinal arteries do not markedly influence the progression of peripapillary atrophy in glaucoma.

SUMMARY

Peripapillary chorioretinal atrophy is one among several morphologic variables to detect glaucomatous abnormalities. Ranking optic disc variables for the detection of glaucomatous optic nerve damage, peripapillary atrophy is a variable of second order. It is useful for the differentiation of various types of chronic open-angle glaucomas. In contrast to glaucomatous eyes, eyes with nonglaucomatous optic nerve atrophy, including eyes after arteritic anterior ischemic optic neuropathy, do not show an enlarged peripapillary atrophy.

Diagnosis and pathogenesis of glaucomatous optic neuropathy: morphological aspects

Glaucomatous optic neuropathy is classified by morphologic changes in the intrapapillary and parapapillary region of the optic nerve head and the retinal nerve fibre layer. These changes can be evaluated using descriptive optic nerve head variables which are the size and shape of the optic disc; size, shape and pallor of the neuroretinal rim; size of the optic cup in relation to the area of the disc; configuration and depth of the optic cup; cup-to-disc diameter ratio and cup-to-disc area ratio; position of the exit of the central retinal vessel trunk on the lamina cribrosa surface; presence and location of splinter-shaped haemorrhages; occurrence, size, configuration and location of parapapillary chorioretinal atrophy; diffuse and/or focal decrease of the diameter of the retinal arterioles; and visibility of the retinal nerve fibre layer. Assessment of these variables is useful for the early detection of glaucomatous optic nerve damage, to follow-up patients with glaucoma, to differentiate various types of the chronic open-angle glaucomas, and to get hints for the pathogenesis of glaucomatous optic nerve fibre loss.

Ophthalmoscopic evaluation of the optic nerve head

Optic nerve diseases, such as the glaucomas, lead to changes in the intrapapillary and parapapillary region of the optic nerve head. These changes can be described by the following variables: size and shape of the optic disk; size, shape, and pallor of the neuroretinal rim; size of the optic cup in relation to the area of the disk; configuration and depth of the optic cup; ratios of cup-to-disk diameter and cup-to-disk area; position of the exit of the central retinal vessel trunk on the lamina cribrosa surface; presence and location of splinter-shaped hemorrhages; occurrence, size, configuration, and location of parapapillary chorioretinal atrophy; diffuse and/or focal decrease of the diameter of the retinal arterioles; and visibility of the retinal nerve fiber layer (RNFL). These variables can be assessed semiquantitively by ophthalmoscopy without applying sophisticated techniques. For the early detection of glaucomatous optic nerve damage in ocular hypertensive eyes before the development of visual field loss, the most important variables are neuroretinal rim shape, optic cup size in relation to optic disk size, diffusely or segmentally decreased visibility of the RNFL, occurrence of localized RNFL defects, and presence of disk hemorrhages.