Stiles-Crawford effect of the first kind: assessment of photoreceptor alignments following dark patching.

Properties of presumed mechanisms controlling photoreceptor alignments are partially defined. A phototropic mechanism normally dominates alignment, but do modest changes in orientations occur with dark patching? Here, new photopic Stiles-Crawford (SCE-I) determinations were made before patching (pre-patch), just after 8-days of dark-patching (post-patch), and 3 days after patch removal (recovery test). We tested at 0, 11 and 22 degrees in the temporal retina of both eyes. Ten eyes of adult subjects were tested. SCE-I peak positions and Stile's parameter 'rho' were assessed. Dark-patching effects were small. Observations revealed meaningful corrective alignment overshoots with recovery in the light. Results suggest (1) the presence of multiple weak mechanisms affecting receptor alignments in the dark; (2) the phototropic mechanism to be dominant in the light; (3) the need for multiple test loci to be sampled in such studies, and (4) small changes in the SCE-I in the pupil plane can reflect meaningful events occurring at the retina.

Performance on the three-point Vernier alignment or acuity test as a function of age: measurement extended to ages 5 to 9 years.

The three-point Vernier alignment (or acuity) test was conducted on children from 5 to 9 years old. There is a significant difference between the 5-9 year old subjects and those in age groups 10 to 19 and 20 to 29 years in Vernier performance. These data were also compared with previously published data from older subjects (up to age 70). We conclude that Vernier function has not fully matured within the age range of 5 to 9 years; this finding is consistent with previous results reported in the literature.

The three point vernier alignment or acuity test (3Pt VA test): an analysis of variance.

A very useful clinical vernier acuity or vernier alignment test has been developed in this and associated laboratories over a span of two decades. We seek to refine further this test, to seek internal inconsistencies and to optimize parameters used in a variety of devices and environments. Vernier testing, and many aspects of this work have been considered by numerous able scientists over a long time period (not reviewed here), but none have encountered conditions faced by this group, particularly in the developing world. The three point vernier alignment (acuity) threshold test (3Pt VeA test) employed here has broad applications; it can be used as a clinical test of vision status, for triage, and as a reference standard for vision testing (in general). As one example, if sufficient luminance is employed, the test is applicable in the presence of truly dense media disorders, even advanced leucomas, mature cataracts, intraocular bleeds, as well as combinations of these disorders, with or without a window to the retina. Only retinal and centrally-based neural disorders, eccentricity from fixation, and about 50% of hypermature cataracts affect outcomes. With minor alterations, this test can be employed to assess the visual field. An analysis of variance (ANOVA) was performed on a defined set of parameters, to enable us to understand better the special properties and requirements associated with this test. Results are not significantly altered between ages 10-94 years (not assessed here). Employing settings well above threshold for test spot detection and well separated individual test spots, changes in test spot luminance, or background luminance (or adaptation level), contrast, veiling glare, test spot size, clear and variously degraded images, seem not to affect meaningfully measured outcomes. If an observer can define well a center of gravity for each test spot viewed, he can align the three points with remarkable precision.

Duplication of unique optical effects of ancient Egyptian lenses from the IV/V Dynasties: lenses fabricated ca 2620-2400 BC or roughly 4600 years ago.

Ancient (in fact, first known) lenses (ca. 4600 years ago) mainly from the IVth and Vth Dynasties of Egypt had truly remarkable and unique optical properties. These were parts of equally fascinating eye structures. These structures were fabricated as separate assemblies for insertion into funerary statues during certain brief windows of time (roughly from 2620-2400 BC, and 1750-1700 BC). These "eyes" appear to follow the observer as he/she rotated in any direction about these statues. In this paper, by simple means, we have recreated the optical properties of these unique lenses in the laboratory in order to help understand their special properties.

Forever young: visual functions not affected or minimally affected by aging: a review.

Six visual functions, once developed to adult levels of performance, have been noted to exhibit little or no alteration with aging (also see Appendix, Note 1). Those selected for more substantial discussions in this article are: (a) the Stiles-Crawford effect of the first kind (SCE-I), also known as the "directional sensitivity of the retina"; (b) specific vernier acuity paradigms (including alignment of two lines one with the other, and two- and three-point vernier alignment tasks); and (c) color vision-related perceptual constancies. Each of these functions has rather different origins in the visual system. The SCE incorporates optical waveguide photoreceptor properties and has both physical and physiological origins; vernier acuity (one of the hyperacuities) is largely the result of neural data processing mechanisms; and the color vision-related effects have their origins in retinal neural processes. Descriptions of additional visual functions minimally affected by age are presented as well. This recent research raises many questions. How can these visual responses be so stable, when so many other visual responses show decrements with aging? What does it mean if anomalous responses within the more stable functions are encountered in individuals? Can these age-resistant functions be employed to help sustain other functions in aging individuals? Are such relatively invariant functions limited to the visual system? Because of the stability of the reported responses with aging, these same relationships can be used as test controls for other studies of aging, and as benchmarks to distinguish between "normal" aging and disease processes.

Refractive astigmatism acts predominantly as a source of high spatial frequency image distortion: the associated lineal distortions can be overcome by using a low pass spatial filter!

PURPOSE: Surprisingly, an important characteristic of astigmatism has been overlooked by ophthalmic and clinical scientists. Apparently, refractive astigmatism is due largely to a form of high spatial frequency image distortion. METHODS: Characteristic astigmatic image distortion can be minimized or eliminated by using a low-pass spatial filter (here, a ground glass plate was employed for this purpose). The ground glass is placed a short distance in front of a visual acuity chart, or it may be used with other tests, such as vernier acuity. RESULTS: This test has been performed by us on large numbers of patients and test subjects. A clinician can try this test for himself/herself. Place a +2.00 D.C. (any axis) lens in front of the eye; the usual distortions will be observed. Locate the ground glass plate as described. The usual distortions associated with the conoid of Stürm will not be visible or will be virtually eliminated, although some image blur will remain. CONCLUSIONS: This technique has significance, e.g., in visual screening programs in developing nations, or in assessing patients with media disorders prior to ophthalmic surgery.

Quantification of prism induced metamorphopsia as a model for clinical retinal (and other) distortions.

Metamorphopsia (all causes) results in perceived distortions in the visual field. A simple technique utilizing hyperacuity judgements was developed in this laboratory some years ago to allow quantification of such distortions. We ask here, how good is this assessment method at detecting a distortion? To control better investigations of metamorphopsia, a model providing constant optical distortions and resultant perceptual metamorphopsia was devised using plane prisms of 8 delta and 15 delta. The instrument includes a beamsplitter and a CRT display controlled by an IBM PC computer and 'mouse'. In this study, three short vertical lines (perpendicular to the prism base-apex line) were used to assessed image distortion in the central retinal area. Positions of individual lines of this pattern were varied in order to determine perceived distortions induced by a prism. Normal observers were tested on multiple occasions. It is possible to measure accurately prism-induced directional biases (mean locations) using this method. We separated personal setting biases from the prism-related distortions. The test method devised mimics modest clinical metamorphopsia. Prism magnitude affected settings. We were able to make judgements to less than +/- 2% error.

Management of aniseikonia after intraocular lens implantation or refractive surgery.

BACKGROUND: Aniseikonia is a difference in perceived image size in the two eyes resulting in asthenopic symptoms and distortions of binocular space perception. This is a complication of refractive and implant surgery in patients with binocular vision. While many individuals adapt readily to modest aniseikonic errors, quite a number do not. METHOD AND RESULTS: Few instruments exist to adequately test for aniseikonia. A means is described to determine if aniseikonia exists and a series of simple steps is suggested to minimize aniseikonia induced by refractive surgery or by surgery for removal of cataract and intraocular lens insertion. Also, using the proposed protocol, it is possible to determine if existing image size differences resulting from prior and/or induced aniseikonia are predominantly refractive or axial. A case report is presented. CONCLUSIONS: The techniques described are not costly, provide no risk, take little time, and resolve or meaningfully reduce aniseikonia in many patients having non-extreme errors of this type.

Photoreceptor orientation and alignment in nasal fundus ectasia.

BACKGROUND: We investigated whether Stiles-Crawford (SCE) functions, a measure of photoreceptor orientation and alignment, are disturbed in patients with nasal fundus ectasia (tilted disc; Fuch's coloboma without apparent pupillary involvement). METHODS: SCE functions were obtained in three observers with nasal fundus ectasia, using psychophysical methods. RESULTS: In all cases, disruption of photoreceptor alignment can be inferred. Results include location of the SCE peaks outside the pupil in the direction of the lesion, differential alignment, and reduction of the magnitude of SCE at various retinal loci (reduced curvature or p factor). Additional results obtained with the selective adaptation technique imply that receptor disarray (splaying) may be responsible for loss of retinal directional sensitivity. CONCLUSIONS: From these results, it may be surmised that mechanical tractional forces can play a major role in defining photoreceptor orientation in the retina. Inferred anomalous photoreceptor alignment has heretofore not been specifically linked with Fuch's coloboma/tilted disc syndrome.

Early lens use: lenses found in context with their original objects.

The early history of optical lenses is poorly defined. Lens-like objects were used for jewelry or decorations for thousands of years, and technology necessary to make lenses was available. In antiquity, a number of activities would have benefited from image size enhancement, and a few lens-like objects have been found at sites where lens use was logical. Means for enhancing visibility of objects have been suggested. Two alternative positions are considered in modern literature: (1) Lenses existed and (2) Fine close work was executed by relatively young and/or nearsighted individuals. Neither argument meets necessary and sufficient conditions for proof of the existence of or lack of lens use. Both forms of image size enhancement might have co-existed, and added factors such as ambient illumination, contrast between the object examined and its background, and shadows must have affected visibility of items viewed. Most probably, optical properties of lens-like elements were appreciated often, across time, by artisans. What is not clear is to what extent general use of lenses resulted. Here, I draw attention to a number of individual lens-like artifacts and the objects intended to be viewed through them. All were decorative pieces or articles of jewelry. The existence of such artifacts has been reported previously. The unique feature in each case presented here is that the lens-like element and object to be viewed were permanently linked together, i.e., "frozen" in time and space. It can be inferred that at least the artisan appreciated the resulting optical effects. Clearly, too, the artist/artisan had to intend the object to be viewed through the lens. This analysis provides an additional useful approach to assessment of early lens use.

Hyperacuity test to evaluate vision through dense cataracts; research preliminary to a clinical study. IV. Data on patients with macular degeneration and minimal media disorders obtained with and without a pseudo-nuclear cataract 6/60 (20/200) at the Aravind Eye Hospital, Madurai, India.

Using a recently discussed three-point Vernier alignment test, data were obtained on patients with macular dysfunctions with and without a pseudo-nuclear cataract 6/60 (20/200) at the Aravind (Free) Eye Hospital, Madurai, India. The pseudo-cataract caused measurably and predictably reduced Vernier alignment thresholds, and necessary modifications deemed to be necessary in the protocol for later study are defined.

Hyperacuity test to evaluate vision through dense cataracts; research preliminary to a clinical study. III. Data on normal subjects obtained with and without a pseudo-nuclear cataract 6/60 (20/200) at the Aravind Eye Hospital, Madurai, India.

Using a recently discussed three-point Vernier alignment test, data were obtained on normal subjects with and without a pseudo-nuclear cataract 6/60 (20/200) at the Aravind Eye Hospital, Madurai, India. This experiment is a critical control exercise. The pseudo-cataract caused measurably and predictably reduced Vernier alignment thresholds, there were no meaningful differences between eyes, and necessary modifications in protocol for a later clinical study were defined.

Performance on three-point vernier acuity targets as a function of age.

With certain (but not all) vernier acuity (VeA) stimulus displays observers exhibit no or slight performance decrements with aging. Because three-point VeA test displays are much more easily applied experimentally and clinically, we examined visual performance on this task as a function of age. Ages of groups tested ranged from 20 to 70+ years (some individuals were 90+ years old). Eyes were examined monocularly. We tested three- and two-point sharply defined VeA arrays and a three-point ground-glass-degraded display (simulating a 20/100 nuclear cataract). Gap or feature separations were varied. Results obtained with the three-point display showed little alteration with age. Image degradation resulted in reduction in performance when small gap separations were used between the test points, but only slight decrements for large gap separations were recorded. The finding that performance with certain VeA targets is largely unaffected by age is confirmed and is expanded.