Stanley Woo

Reading speed does not benefit from increased line spacing in AMD patients.

Purpose. Crowding, the adverse spatial interaction due to the proximity of adjacent targets, has been suggested as an explanation for slow reading in peripheral vision. Previously, we showed that increased line spacing, which presumably reduces crowding between adjacent lines of text, improved reading speed in the normal periphery (Chung, Optom Vis Sci 2004;81:525–35). The purpose of this study was to examine whether or not individuals with age-related macular degeneration (AMD) would benefit from increased line spacing for reading. Methods. Experiment 1: Eight subjects with AMD read aloud 100-word passages rendered at five line spacings: the standard single spacing, 1.5×, 2×, 3×, and 4× the standard spacing. Print sizes were 1× and 2× of the critical print size. Reading time and number of reading errors for each passage were measured to compute the reading speed. Experiment 2: Four subjects with AMD read aloud sequences of six 4-letter words, presented on a computer monitor using the rapid serial visual presentation (RSVP) paradigm. Target words were presented singly, or flanked above and below by two other words that changed in synchrony with the target word, at various vertical word separations. Print size was 2× the critical print size. Reading speed was calculated based on the RSVP exposure duration that yielded 80% of the words read correctly. Results. Averaged across subjects, reading speeds for passages were virtually constant for the range of line spacings tested. For sequences of unrelated words, reading speeds were also virtually constant for the range of vertical word separations tested, except at the smallest (standard) separation at which reading speed was lower. Conclusions. Contrary to the previous finding that reading speed improved in normal peripheral vision, increased line spacing in passages, or increased vertical separation between words in RSVP, did not lead to improved reading speed in people with AMD.

Beating the beat : Reading can be faster than the frequency of eye movements in persons with congenital nystagmus

Purpose. Rapid serial visual presentation (RSVP) of text has been reported to foster higher reading rates than presentation in a continuous text (CT) format, possibly because scanning eye movements are minimized. We investigated how this might be relevant for persons with congenital nystagmus (CN). Methods. We evaluated whether reading rates differ in persons with CN for RSVP versus CT presentation of single sentences under otherwise similar conditions. In a second experiment, we presented unrelated words to observers with CN in RSVP format while measuring their eye movements to determine whether reading can occur during the high-velocity, nonfoveating periods of the CN wave form. Both sentences and random words were selected from the MNRead corpus and displayed at 2x, 4x, or 8x the threshold word size on a 21-inch computer monitor. Results. Subjects with CN have virtually equivalent maximum reading speeds of 449 and 448 words per minute, respectively, for RSVP and CT presentation of sentences. Typically, reading rates were faster than the frequency of CN, which suggests that subjects could read during the nonfoveating periods of the nystagmus waveform. This finding was confirmed using random words that, unlike those in sentences, cannot be inferred from contextual cues. Examination of eye movements recorded during reading indicated that random words are read correctly with 47% to 65% accuracy (depending on word size) during the nonfoveating periods of the CN waveform. Conclusion. A clinical implication of these results is that reading performance in persons with CN should be facilitated by large text sizes that remain legible during a greater fraction of the CN waveform.

Orientation discrimination with macular changes associated with early AMD.

Purpose. Age-related macular degeneration (AMD) is a condition that progressively reduces central vision in elderly individuals, resulting in a reduced capacity to perform many daily activities and a diminished quality of life. Recent studies identified clinical treatments that can slow or reverse the progression of exudative (wet) AMD and ongoing research is evaluating earlier interventions. Because early diagnosis is critical for an optimal outcome, the goal of this study is to assess psychophysical orientation discrimination for randomly positioned short line segments as a potential indicator of subtle macular changes in eyes with early AMD. Methods. Orientation discrimination was measured in a sample of 74 eyes of patients aged 47 to 82 years old, none of which had intermediate or advanced AMD. Amsler-grid testing was performed as well. A masked examiner graded each eye as level 0, 1, 2, or 3 on a streamlined version of the Age-Related Eye Disease Study (AREDS) scale for AMD, based on the presence and extent of macular drusen or retinal pigment epithelium (RPE) changes. Visual acuity in the 74 eyes ranged from 20/15 to 20/40+1, with no significant differences among the grading levels. Humphrey 10–2 and Nidek MP-1 micro-perimetry were used to assess retinal sensitivity at test locations 1° from the locus of fixation. Results. Average orientation-discrimination thresholds increased systematically from 7.4° to 11.3° according to the level of macular changes. In contrast, only 3 of 74 eyes exhibited abnormalities on the Amsler grid and central-field perimetric defects occurred with approximately equal probability at all grading levels. Conclusions. In contrast to Amsler grid and central-visual-field testing, psychophysical orientation discrimination has the capability to distinguish between eyes with and without subtle age-related macular changes.

A study of the central and peripheral refractive power of the cornea with orthokeratology treatment

Abstract The central and peripheral refracting power of the cornea after orthokeratology treatment was studied by a cross-sectional method. Three Asian subject groups were recruited. Group 1 consisted of 31 normal non-contact lens wearers, group 2 consisted of 14 subjects who wore orthoK contact lenses for 10–20 months, and group 3 consisted of 14 subjects who wore orthoK contact lenses for more than 20 months. Our results showed that the corneal refracting power (central 3.3 mm) in both of the groups with orthoK contact lens treatment did not differ significantly from the average cornea. The group that wore orthoK lenses for more than 20 months had a flatter temporal peripheral cornea than did the normal group at approximately 2.95 mm from the corneal apex. Because the temporal cornea is steeper than the nasal cornea in normal eyes, a relatively flatter temporal cornea in the orthoK group produces a more symmetrical peripheral cornea.

Fixation locus in patients with bilateral central scotomas for targets that perceptually fill in.

Purpose In this experiment, we investigated whether target type affects the retinal fixation location and stability in patients with bilateral central scotomas and, specifically, whether targets expected to perceptually fill in are imaged at or near the vestigial fovea. Methods The retinal location and stability of fixation were measured using the Nidek MP-1 microperimeter in 12 patients with bilateral central scotomas for six types of fixation target, three expected to fill in and three that included letters. The approximate position of the vestigial fovea was delineated in 10 of the patients either by using residual retinal landmarks or by locating the residual foveal pit in a dense macular scan obtained with a Spectralis optical coherence tomographer. Fixation location and stability were compared for the different target types and referenced to the position of the vestigial fovea. Results All of the subjects except one fixated consistently on targets that included a letter using peripheral retinal locations outside of the central scotoma. Eleven of the 12 subjects used a retinal location closer to the vestigial fovea to fixate targets expected to fill in compared with letters. Although four of the subjects imaged the filled-in targets at or within a half degree of the vestigial fovea, six other subjects imaged the filled-in targets at a retinal locus removed from the vestigial fovea. Target type produced no overall significant difference in fixation stability, specified in terms of bivariate contour ellipse area. However, in some individual subjects, fixation tended to be more stable on letter targets than on filled-in targets. Conclusions In patients with central field loss, letter targets generate more consistent fixation behavior than filled-in targets and should be used for eccentric viewing training and perimetry.

The need for full scope primary eye care in every country

Affordable and accessible comprehensive eye and vision health care for all citizens is a goal for every country. Leadership from a number of developed countries has helped in the policy development and professional aspirations of optometry but there have also been lessons learned from experiences in providing better eye care in developing countries that have challenges of a different kind and magnitude. Casting a broad net and expanding dialogue through associations and individuals are the first steps in accomplishing our collective goals. Supranational health bodies, like the World Health Organization (WHO) and global eye-health initiatives, like VISION 2020, have continually highlighted the urgency to address the leading cause of avoidable blindness worldwide and arguably the easiest to diagnose and treat— refractive errors. It was estimated by WHO in 2010 that uncorrected refractive error is liable for about 43 per cent of the 285 million people who suffer visual impairment worldwide. Yet despite their efforts, uncorrected refractive errors, including presbyopia, are still significant problems even in some developed countries. Various factors are contributing to this sad state of affairs, such as failure to recognise the magnitude of the problem, the economic weakness of the country or the immaturity of its structures of government, the lack of appropriately trained and properly distributed eye-care practitioners and the educational infrastructure to produce them. There is also a confusing plethora of different types of personnel who provide varying and sometimes overlapping elements of ocular and visual health care. It does not help matters, when there are also many different models of formal education and scopes of practice around the world for the two main branches of ocular and visual health, namely, optometry and ophthalmology.

Vision Impairment Assessment and Assistive Technologies

Low vision refers to a condition of irreversible vision loss that is not correctable by conventional spectacles, contact lenses, surgery, or medicine. The ocular disease leads to a visual impairment that results in a functional limitation of the eye or visual system. This may include a reduction in detail vision (visual acuity), side vision (peripheral visual field), distorted or double vision, or a combination thereof. The consequence of this impairment may lead to a visual disability that prevents the person from performing specific tasks such as reading, driving, cooking, or watching television. Depending on the severity of the disability, the result may be a visual handicap that may lead to a loss of personal and/or socioeconomic independence. Much work has been done in an attempt to classify the interaction of visual impairment, disability, and handicap in an effort to characterize the impact of low-vision rehabilitation (LVR) as a treatment modality [1, 2]. LVR embraces an inter-disciplinary approach to ameliorating the handicap and maximizing quality of life for the partially sighted [3]. Eligibility for services for the elderly for LVR often depends on categorizing the level of visual impairment, specifically whether a person is “legally blind” or “visually impaired.” The Social Security Administration defines “legal blindness” as best corrected visual acuity in the better seeing eye that is 20/200 or worse. Alternatively, it may be characterized by a visual field less than 20◦ in diameter in the eye with the larger remaining field [4]. Visual impairment describes vision that does not meet the criteria for legal blindness but may still result in a visual disability or handicap. These are codified in the “International Classification of Diseases, 9th Revision, Clinical Modification” (ICD-9-CM), Sixth Edition, based on the combination of vision (visual acuity and/or visual field) in each eye. The ICD-9 codes are essential for documentation and billing for rehabilitative services (Table 6.1).