The relationship between word length and threshold character size in patients with central scotoma and eccentric fixation

Background Understanding limitations on text reading with eccentric fixation is of major concern in low vision research. Our objective was to determine, in patients with a central scotoma, whether threshold character size is similar for different word lengths and paragraphed texts.Methods In 19 patients, we retrospectively analyzed the relationship between minimum readable character size for isolated words and text. Isolated letters, two, five, and ten-letter words and a paragraphed text were presented randomly through a scanning laser ophthalmoscope in eight different character sizes.Results Threshold character size varied according to the text stimulus (p<0.05). Threshold character sizes for single letters and two-letter words were matched (p>0.99), as were those for five-letter words, ten-letter words, and paragraphed text (p>0.99). Threshold character size for single letters and two-letter words was significantly lower than that measured with other text stimuli.Discussion Reading performance is influenced by a variety of factors such as crowding, contextual effects, visual span, degree of oculomotor adaptation needed, and frequency of a defined word. Globally, when reading with a central scotoma, it appears that within word characteristics have more impact than inter-word parameters on threshold character size.     

Postoperative astigmatism after central vs eccentric penetrating keratoplasties

Six patients with markedly eccentric penetrating keratoplasties had severe corneal astigmatism (mean, 10.38 +/- 2.91 diopters). In four of these patients the flat meridian was lying in the direction of graft displacement. Laboratory experiments disclosed no statistically significant difference in diameter between the major and minor axes of the corneal buttons in the centrally and eccentrically trephined eyes and we could not elucidate the mechanism of the severe astigmatism. However, in the eccentrically trephined eyes the longer axis consistently lay in the direction of decentration whereas in the centrally trephined eyes the long axis was oriented randomly.     

Eccentric fixation with macular scotoma

People with macular scotoma tend to read and visually scan more slowly than others with equivalently reduced visual acuity but intact central fields. We measured fixation eye movements and considered the contribution of fixation variability and centripetal eye drift to poor visual performance. These factors might confound efforts to consistently use an optimum retinal locus outside of the macula. We measured monocular horizontal and vertical eye movements using a search coil eyetracker while subjects with naturally occurring central scotomata or control subjects with simulated scotomata eccentrically fixated a single character that was sized to their visual acuity. Motivated subjects with long-standing stable maculopathies were chosen to estimate attainable performance limits. During attempts to eccentrically fixate, an ubiquitous foveal pursuit or centripetal drift tendency was not found; rather a pattern of drift was idiosyncratic from subject to subject. This finding was confirmed by an analysis of eye drift of 32 eyes with long-standing bilateral macular scotomata. Moreover, the eye drift speeds (15-200 minarc/sec) were too low to be of functional significance. Drift speeds during eccentric fixation with a visible target were not significantly different than those after the target was extinguished; however, drift speeds were greater than during foveal fixation. This suggests that the fovea has a specialized control of slow eye movements. Fixation variability increased with scotoma size for both simulated and real scotomata, with an abrupt rise when scotomata diameters exceeded 20 degrees C. A significant minority of subjects (39%) adopted two or more distinct preferred retinal loci (PRL) during fixation. Multiple PRL were also more likely if scotoma size exceeded 20 degrees C. Reasonably steady fixation is thus attainable when central scotoma sizes are smaller than approximately 20 degrees C.     

A computer and video display based system for training eccentric viewing in macular degeneration with an absolute central scotoma

A new approach designed to establish the most suitable area for eccentric viewing and to teach and train patients with severe age-related macular degeneration (AMD) to use the eccentric viewing technique is described. Using a computer and video display based system, as well as software written specifically for this purpose, we investigated and trained ten consecutive patients with AMD. The patients were 80.1 ± 5.6 years old, on average. All of them had an absolute central scotoma. Mean visual acuity was 0.035 ± 0.016. After 30 min of testing, instruction and reading on the screen, followed by 2.6 ± 0.69 one-hour training sessions, on average, with the low vision therapist, reading newspaper and book texts with the aid of hyperoculars or aplanatic systems and a very short reading distance, the patients achieved a reading speed of 58.9 ± 19.7 words/min, significantly (p<0.001) higher than the initial speed when reading on the screen, 11.5 ± 4.5 words/min.     

斜视性弱视伴偏中心注视眼的多焦视网膜电图表现

目的：探究斜视性弱视伴偏中心注视眼的多焦视网膜电图(mfERG)特征性变化。

方法：收集2018-01/2020-12在我院就诊的斜视性弱视伴偏中心注视患者20例作为研究组(4例为外斜视,16例为内斜视),同时收集屈光不正性弱视患者20例作为对照组。散瞳状态下检查mfERG,记录P1波的振幅密度和潜伏期。

结果：斜视组弱视眼多焦视网膜电图P1波振幅密度与対侧眼相比第一环(P=0.001),第二环(P<0.001),第三环(P=0.001),第四环(P=0.009),第五环(P=0.026)明显降低; 与对照组相比第一环(P=0.033),第二环(P=0.002),第三环(P<0.001),第四环(P=0.014)明显降低; 斜视组弱视眼潜伏期与対侧眼相比第一环(P=0.017)、第二环(P=0.001)有明显缩短,与对照组相比第二环(P=0.007)明显缩短。

结论：斜视性弱视伴偏中心注视眼的多焦视网膜电图P1波振幅密度越靠近黄斑中心凹下降越多,且与屈光不正性弱视眼相比下降更多。     

青光眼中央暗点型视野损害特点分析

目的　探讨发生于青光眼的中央暗点所具备的临床特征。方法　回顾性非对照的研究。从青光眼患者的视野资料当中筛选中央暗点 ,分析暗点的形态和分布特点、进展情况、受累眼的视力以及相应的眼底改变 ,计算其在青光眼早期视野改变中所占的比率 ,比较该型视野在正常眼压性青光眼、原发性开角型青光眼、原发性闭角型青光眼的早期阶段发生率的差异。结果　发生于青光眼的中央暗点是以水平径线为界的半侧性中央暗点 ,在进展过程中也不跨越该界线 ,而是在同侧扩大加深 ,水平径线侧边界平直 ;在上方视野的发生多于下方视野 ;对视力无明显影响 ;通过存档的彩色立体眼底相片可查见局限性视网膜神经纤维层损害 ,其位置邻近盘斑束。在青光眼早期视野损害当中 ,中央暗点约占 10 5 %。中央暗点可发生于多种类型的青光眼 ,其中 ,三种原发性青光眼的发生情况为 :正常眼压性青光眼 (NPG) 15 9% ,原发性开角型青光眼 (POAG) 7 5 % ,原发性闭角型青光眼(PACG) 5 2 %。在NPG当中的发生率高于高眼压性青光眼 (POAG或PACG) ,其差异具有统计学意义 (P <0 0 5 ) ,POAG与PACG的发生率则无差异 (P >0 0 5 )。结论　发生于青光眼的中央暗点具有自身特征 ,最突出的特点是不跨越水平径线 ,可与其他疾病所致的中央暗点相鉴别 ;发     

Bilateral central scotoma with preservation of central vision in 2 patients following caesarian section under spinal anesthesia

Two female patients are described with acute bilateral central scotomata with preservation of central vision following spinal anesthesia. Both patients had a temporary drop in systemic blood pressure and underwent caesarian section with moderate blood loss.In order to explain the visual field defects extensive ophthalmological examination and CT-scanning with nuclear magnetic resonance imaging were performed. The hypothetical explanation for the visual field defects is transient macular ischemia.     

Scanning characters and reading with a central scotoma

Among the patients we tested, most of those who had lost normal macular function developed extrafoveal retinal loci which resulted in strongly preferred viewing angles for steady fixation. These patients used these extrafoveal retinal loci to scan lines of characters in patterns similar to patients with normal macular function. Although the scanning speed of these patients was adversely affected by their large size scotomas, their reading accuracy was not necessarily reduced. The assessment of scanning and reading performance in this population requires careful measurement of the visual skills involved in reading.     

Reading with a macular scotoma. I. Retinal location of scotoma and fixation area

To investigate how patients with macular scotomas use residual functional retinal areas to inspect visual detail, a scanning laser ophthalmoscope (SLO) was used to map the retinal locations of scotomas and areas used to fixate. Three patients with dense macular scotomas of at least 20 months duration and with no explicit low vision training were tested. SLO stimuli were produced by computer modulation of the scanned laser beam, and could be placed on known retinal loci by direct observation of the retina on a television monitor. Videotaped SLO images were analyzed to produce retinal maps that are corrected for shifts of stimulus position due to fixational eye movement, thus showing the true retinal locations of scotomas and fixation loci. Major findings were as follows: 1) each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma to fixate, and did not attempt to use the nonfunctional foveola, 2) fixation stability with the eccentric fixation locus was as good as, or better than, that of ocularly normal subjects trying to fixate at comparable eccentricities, 3) fixation stability was not systematically related to clinical visual acuity, and 4) there is good agreement as to the shape and overall size of SLO and standard clinical tangent screen scotoma maps for these three patients.     

Optokinetic nystagmus elicited by filling-in in adults with central scotoma

PURPOSE: Filling-in is the perceptual completion of physiological, pathologic, or artificial scotomas. Three patients are described, in whom optokinetic nystagmus (OKN) was present during filling-in. METHODS: Three patients with age-related macular degeneration with large central scotomas were included in the study. OKN was elicited with black and white stripes moving nasally to temporally or temporally to nasally at four velocities. OKN gain was measured using infrared oculography. RESULTS: While looking at the OKN stimuli, the patients either did not see the stimulus (without perceiving a positive scotoma) or filled in the scotoma and perceived the stripes. Simultaneously with filling in the scotoma, OKN eye movements were elicited in all three patients. The filling-in phenomenon was present for all stimulus directions and velocities, appeared within seconds, and was followed immediately by eye movements corresponding to OKN. OKN gains during filling-in were similar to those of age-matched control subjects without scotomas. No asymmetry was noted between temporal to nasal or nasal to temporal stimulation. CONCLUSIONS: Motion-sensitive areas of the visual cortex may be activated and trigger the generation of OKN, supporting an active process. Alternatively, OKN is suppressed when subjects are not filling-in, while the subjects are fixating the central scotoma or edges of the scotoma. That the subjects did not perceive positive scotomas suggests that an active process is more likely.     

Rehabilitative approach in patients with ring scotoma

Objective

To investigate the rehabilitative approach in patients with ring scotoma. A central scotoma is characteristic for patients with age-related macular degeneration (AMD). Sometimes patients with AMD maintain a residual central vision area within the scotoma (ring scotoma).

Design

Prospective, nonrandomized case series.

Participants

Twenty-four patients with AMD.

Methods

A formal low-vision assessment was performed for all study patients. The assessment included best corrected visual acuity (BCVA), contrast sensitivity, reading speed, and microperimetry. All patients were provided a low-vision assessment to satisfy patients’ needs. Devices were prescribed accordingly.

Results

The BCVA found was 0.4 logMAR (SD 0.1). All had central and stable fixation. Residual central retinal area size and sensitivity measured 2.4° (SD 0.8) and 3.1 dB (SD 0.8), respectively. Twenty patients achieved better vision with optical magnification in the eye with ring scotoma. Mean reading speed achieved was 50.2 words/min (SD 20.9). A linear correlation was found for reading speed with both central area sensitivity (r² = 0.5, p < 0.05) and contrast sensitivity (r² = 0.3, p < 0.05).

Conclusions

In patients with AMD with ring scotoma, moderate amounts of magnification seem to provide satisfactory rehabilitation outcomes. Central retinal spared area sensitivity may predict reading speed outcomes, whereas residual central area size is likely to be useful in determining magnification.     

Patients with AMD and a large absolute central scotoma can be trained successfully to use eccentric viewing,as demonstrated in a scanning laser ophthalmoscope

Twenty patients with age-related macular degeneration, an absolute central scotoma and a mean visual acuity of 0.04 (20/475) were studied. A scanning laser ophthalmoscope (SLO) was used for microperimetry and determination of preferred retinal locus, often located to the left of the retinal lesion (corresponding to a location to the left of the visual field scotoma), which is considered unfavorable for reading. All 20 patients were trained to use a new and more favorable retinal locus for reading, above (or occasionally below) the retinal lesion (corresponding to a location below or above the visual field scotoma), first by reading scrolled text under simultaneous fixation monitoring and instruction in the SLO and then by reading printed text, using high magnification (mean 14.3x). For the 18 patients who learned to use eccentric viewing, reading speed with adequate magnification prior to training was 9.0+/-5.8 words/min. With training (mean 5.2 hours), it increased significantly (p<0.001) to 68.3+/-19.4 words per min. Training of eccentric reading has thus proved to be very successful.