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PubMed1997

Variability of the refractive state: meridional profiles and uniform variation.

Variation of the refractive state as measured with autorefraction is the result of many factors which need to be considered if optometry is to develop a more complete understanding of the behavior of the visual process. Various methods can be applied to develop such an understanding including scatter plots, meridional profiles of variance-covariance, and graphs of uniform variation. These methods are used, in this paper, to investigate some results for autorefraction from a sample of 106 university students studying optometry. Some of the eyes in the sample display variation, some or all of whose characteristics are the same in all meridians of the eye. Such eyes are said to exhibit refractive variation that is partially or completely uniform across the meridians of the eye. Most eyes, however, show variation which appears to depart from uniformity. The typical eye in the sample appears to exhibit variation that is mainly spherical in character and of a small magnitude in keeping with the view that the accommodative system mostly is responsible for this variation. Nevertheless, there is an astigmatic component to the variation. The mean variance-covariance matrices for the right and left eyes are presented.

Accommodation, Ocular↗
PubMed1998

Evaluation of the EyeSys model II computerized videokeratoscope. Part I: Clinical assessment.

PURPOSE: To compare the agreement and repeatability of keratometry measurements with simulated keratometry measurements from the EyeSys (model II) corneal analysis system (CAS). Furthermore, to establish any relationship between the repeatability of peripheral corneal measurements and the spatial location at the cornea. METHODS: Measurements using a Bausch & Lomb keratometer in 19 eyes (19 subjects) were compared with the simulated keratometry values using the EyeSys CAS. Repeatability of the keratometer (14 eyes, 14 subjects) and the EyeSys simulated keratometry values (10 eyes, 10 subjects) was assessed by comparing the difference of two measurements. Peripheral repeatability of the EyeSys CAS was compared in a similar manner in a sample of 10 eyes (10 subjects). RESULTS: The 95% confidence limits (-0.529 to +0.149 D) showed a lack of agreement between both instruments. With respect to the repeatability, both the keratometer (SD = +/- 0.103 D) and the EyeSys (SD = +/- 0.072 D) were found to exhibit approximately similar degrees of repeatability. The repeatability of peripheral corneal measurements using the EyeSys CAS showed changes in repeatability dependent on the corneal meridian and the distance from the point of alignment. Measurements along the superior and nasal meridians showed poorest repeatability. Repeatability was also found to deteriorate away from the point of alignment. CONCLUSIONS: EyeSys simulated keratometry values were not interchangeable with the keratometer. This could be due to differences in the method of alignment or measurements from different areas on the corneal surface. Repeatability of both the Bausch & Lomb keratometer and the EyeSys CAS was found to be similar. The spatial dependency of peripheral corneal radius repeatability measurements could be attributed to interference of the ocular adnexa in those areas of measurement.

Cornea↗
PubMed1999

Relationship between anisometropia, amblyopia, and binocularity.

PURPOSE: To determine if higher degrees of anisometropia cause deeper amblyopia and poorer binocularity than lower degrees of anisometropia in children and adults. METHODS: The clinical records for 60 patients with untreated anisometropic amblyopia without strabismus, ranging in age from 3 to 39 years, were reviewed. The refractive error, the initial best corrected visual acuities in the amblyopic and nonamblyopic eyes, and the level of binocularity were recorded from each chart. The degree of anisometropia was determined by: (1) calculating the difference between spherical equivalents for each eye; (2) calculating the difference in the vertical meridians for each eye; (3) calculating the difference in the horizontal meridians for each eye; and (4) calculating the root mean square difference which also takes into account differences in astigmatic axis. The depth of amblyopia was determined by converting the visual acuity score to its logarithmic value, logarithm of the minimum angle of resolution (logMAR), and calculating the difference between the amblyopic and nonamblyopic eye. The level of binocularity was determined from stereopsis testing. RESULTS: For all patients, there was a significant relationship between the four measures of anisometropia, the depth of amblyopia, and the level of binocularity (median correlations 0.61 and 0.61, respectively). For the myopes (N = 10), there was no significant relationship between the 4 measures of anisometropia, the depth of amblyopia, and the level of binocularity (median correlations 0.34 and 0.61, respectively). For the hyperopes (N = 50), the relationship was significant for all 4 measures of anisometropia (median correlations 0.72 and 0.62, respectively). CONCLUSION: As the degree of anisometropia increases, the depth of amblyopia becomes greater and the level of binocularity becomes poorer, at least for hyperopic patients.

Adolescent↗
PubMed2001

Anterior chamber angle anomalies associated with signs of pigment dispersion in a group of black probands and their first-degree relatives.

PURPOSE: To evaluate the presence of iridocorneal angle anomalies associated with signs of pigment dispersion among a group of black probands and their first-degree relatives. METHODS: Eleven blacks who exhibited pigment dispersion syndrome (PDS) signs, including Krukenberg's spindles, moderate-to-heavy trabecular meshwork pigmentation, and peripheral lenticular/zonular pigmentation, received a complete eye examination that included gonioscopy. Overt iridocorneal angle abnormalities other than pigment deposition were photo-documented. Twenty-two first-degree relatives (6 siblings, 15 children, and 1 parent) of these probands underwent similar examination. RESULTS: Among the subjects, 5 of 11 probands (age range 13 to 59 years) and 4 of 22 relatives (age range 14 to 51 years) exhibited definite angle anomalies. The nine subjects with angle anomalies belonged to 7 of 11 separate families. The four relatives with angle anomalies did not have PDS according to our criteria, but two other relatives from two additional families did have signs consistent with clinical PDS. Types of angle anomalies included (1) peripheral anterior synechia-like lesions; (2) a prominent concavity of the peripheral iris at the 6-o'clock meridian; (3) a whitish, thread-like band of tissue near the iris base; (4) a prominent, externally-visible Schwalbe's line at the 6-o'clock meridian; and (5) a prominent, web-like confluence of exaggerated iris processes 360 degrees along the angle wall. Iris processes and prominent Schwalbe's lines were not considered abnormal or anomalous unless they were clearly atypical. CONCLUSIONS: Iridocorneal angle anomalies, other than pigment deposition, were common among our black group who exhibited signs of pigment dispersion as well as among their first-degree relatives. Further consideration should be given to the possibility that among some patient groups, overt goniodysgenesis could be part of a constellation of signs indicative of a pigment dispersion syndrome. Potentially, clinically detectable goniodysgenesis could prove to be a useful marker to identify certain subjects who carry PDS genetic traits but who have not expressed complete phenotypical disease.

Adolescent↗
PubMed2001

The binocular accommodative response in uncorrected ametropia.

PURPOSE: To measure the changes in astigmatism and in the degree of anisometropia when ametropes respond to accommodative stimulation. METHODS: The accommodative responses of ametropes were binocularly measured with an improved photorefractometer (PR-1100), which objectively measured binocular refraction in all meridians simultaneously, when a visual fixation target was shown in natural space at 5 and 0.5 m. RESULTS: (1) Changes of astigmatism and anisometropia occur during binocular accommodation. (2) Changes of astigmatism mainly result from lag of accommodation in the horizontal meridian. (3) Changes of anisometropia result from the effort to focus. (4) The interaction of both eyes is suggested as the cause of the changes of astigmatism and anisometropia with accommodation. (5) In the majority of strong anisometropes (nonoverlapping group in this paper), the magnitude of anisometropia decreases (approaching isometropia) with accommodation. CONCLUSION: Changes in astigmatism and anisometropia can occur during accommodation, and these interactions of both eyes with accommodation may contribute to the development and maintenance of binocular function.

Accommodation, Ocular↗
PubMed2001

Does meaning matter? The impact of word knowledge on lateral masking.

BACKGROUND: Many older adults have lost the use of their foveae due to disease. Because of this, they must use peripheral retina to do tasks formerly done using the fovea, such as letter identification and reading. Several researchers have recently proposed that reading in the periphery is limited by lateral masking: the reduced perceptibility of a target when it is surrounded by flanking stimuli. None of these studies tested the perceptibility of letters within words, where the semantic relationship between the target letter and the flanking letters is likely to improve perceptibility. This study sought to determine whether the semantic relationship between the flanking stimuli and the target stimulus affects perceptibility of letters in the periphery. METHODS: Young, normally-sighted observers identified single letters and the middle letters of three-letter words, trigrams, and letters flanked by x's (xax) presented for 150 ms at 10 degrees eccentricity on each of the primary meridia. In the first experiment, subjects identified letters presented alone and letters flanked by one x on either side. In the second experiment, subjects identified the middle letters of words, trigrams, and xax stimuli, which were either presented in blocks or randomly. In the third experiment, only the words and trigrams were used, and subjects were required to both identify the middle letter and simultaneously indicate whether the stimulus was a word or a trigram. RESULTS: The first experiment showed that single letters were identified about 50% more accurately than letters flanked by x's. In the second and third experiments, letter identification was better when the target and flanking letters formed a word than when they formed a trigram and better along the horizontal meridian than along the vertical meridian, which is consistent with previous studies. In the third experiment, the subject's ability to identify the stimulus type had a significant impact on performance. When the stimuli were words, subjects identified the middle letter on 87% of trials when they correctly identified the stimulus and 40% of the trials when they did not; for the trigrams these percentages were 65% and 5%. CONCLUSIONS: When the flanking letters and the target letter formed a word, observers were better able to identify the target than when they did not form a word, and this pattern was mediated by the observers' knowledge of stimulus type. These data suggest that to draw conclusions regarding the impact of lateral masking on reading, the stimuli used should be words, not random-letter strings or other target/flanker combinations.

Adult↗
PubMed2003

What are the visual benefits of eyelid squinting?

PURPOSE: We propose that eyelid squint can reduce the impact of several conditions known to cause eyestrain such as uncorrected refractive error, accommodative dysfunction, presbyopia, and glare. Clinicians commonly accept that squint improves visual acuity (VA) in the presence of refractive error, and even though the benefit of eyelid squint in bright light seems self-evident, data are not available to support either benefit. The purpose of this study was to measure the effect of eyelid squint on VA in the presence of refractive blur and on visual field sensitivity. METHODS: Nineteen subjects with optimal refractive correction were tested, with and without squinting, as follows: (1) distance VA with induced refractive errors of +0.50, +1.00, +2.00, +3.00, +1.00 -1.00 x 90, and +1.00 -1.00 x 180; (2) near VA with induced refractive errors of -1.00 x 90 and -1.00 x 180; and (3) central and peripheral threshold visual fields with a Humphrey Field Analyzer. Differences in visual acuity between squinting and nonsquinting were tested for significance with repeated-measures analysis of variance, and differences in visual fields were tested using mixed model analysis of variance with repeated measures. RESULTS: Eyelid squint significantly improved (p < 00.016) distance VA measurements for 1.00 to 3.00 D of induced myopia. The squint-induced VA improvement increased from 0.06 logarithm of the minimum angle of resolution for 1.00 D to 0.24 logarithm of the minimum angle of resolution for 3.00 D of myopia. Eyelid squint also significantly reduced visual field sensitivity below the horizontal meridian by an average of 1.4 dB, by 1.6 dB on the horizontal meridian, and with increasing reductions in the vertical field up to 11.6 dB for measurements 40 degrees above fixation. This pattern of decreased superior field sensitivity would decrease visual discomfort from overhead glare. CONCLUSIONS: The results provide empirical support that eyelid squint improves visual acuity for subjects with refractive error and reduces glare in the superior visual field.

Adult↗
PubMed2001

Foveal ectopia in X-linked retinoschisis.

BACKGROUND: This study compared the position of the foveal center in patients with X-linked retinoschisis (XLRS) and controls and estimated the frequency of foveal ectopia in XLRS. METHOD: Fundus photographs of 23 patients with XLRS and 25 controls were reviewed. The position of the foveal center relative to the vertical center of the optic disk was determined from magnified images and expressed as the angle between the disk and foveal centers, relative to the horizontal meridian. The shortest distance between the foveal and disk centers was also measured, using the horizontal disk diameter (HDD) as the relative size unit. RESULTS: The position of the foveal center could be determined accurately for 43 eyes of the 23 patients with XLRS. The foveal center was located an average of 4.7 degrees (standard deviation, 9.3) below and 3.2 HDD (standard deviation, 0.4) temporal to the vertical disk center. In 9 (21 %) of the eyes, the fovea was above the horizontal meridian. For the control eyes, the foveal center was an average of 7.8 degrees (standard deviation, 2.3) below and 2.9 HDD (standard deviation, 0.4) temporal to the vertical disk center. According to a previous definition, foveal ectopia was present in 13 (30%) of the eyes with XLRS and none of the control eyes (P < 0.001). CONCLUSION: Foveal ectopia occurs in at least 30% of eyes with XLRS. This finding may provide a useful diagnostic sign for XLRS and may have implications for its pathogenesis.

Eye Abnormalities↗
PubMed2004

Recurrent vitreous hemorrhage after sutured posterior chamber intraocular lenses.

PURPOSE: To describe the clinical course and management of patients with late vitreous hemorrhage after scleral suturing of posterior chamber intraocular lenses (PCIOL). METHODS: The authors reviewed patient demographics, ocular findings, and clinical course of six patients with late (>3 weeks) vitreous hemorrhage after sclera-sutured PCIOL. Intraoperative endoscopy was performed on two patients to better assess the haptic sulcus interaction. RESULTS: Patient age ranged from 39 to 84 years (median 77 years). The interval between scleral suturing of the PCIOL and vitreous hemorrhage ranged from 3 weeks to 68 months (median 5 months). The number of hemorrhages ranged from one to four. The hemorrhage cleared spontaneously in three eyes. Three patients underwent surgery after the hemorrhages including sutured PCIOL removal with concurrent placement of an anterior chamber IOL (ACIOL) (two patients) and resuturing of a PCIOL in a different meridian (one patient). Follow-up ranged from 4 to 36 months, median 19.5 months, starting from the time of the initial postsuturing vitreous hemorrhage. Final vision ranged from 20/20 to hand motions, with four eyes having 20/40 or better vision. Endoscopy revealed a haptic embedded into the pars plicata in one eye but no evidence of neovascularization. CONCLUSION: Recurrent vitreous hemorrhage may occur as a complication of scleral suturing of PCIOL. The etiology of these hemorrhages does not appear to be related to neovascular proliferation at the haptic suture site, but may be secondary to erosion of the haptic into uveal structures. Not all eyes require reoperation after these hemorrhages; however, good visual results may be achieved by replacing the sutured PCIOL with an ACIOL or by suturing the PCIOL in a different meridian.

Adult↗
PubMed2002

Serologic herpes testing in the real world: validation of new type-specific serologic herpes simplex virus tests in a public health laboratory.

BACKGROUND: Serologic testing for herpes simplex virus type-2 (HSV-2) is being implemented in sexually transmitted disease (STD) clinics. GOAL: To determine the performance characteristics of two HSV-2 type-specific serologic assays in a public health laboratory. STUDY DESIGN: Sera stored from a cross-sectional study were tested with the Meridian Diagnostics and Focus Technologies HSV-2 ELISA tests and a type-specific strip immunoblot assay (Chiron Corp.) was used as the reference standard. RESULTS: Prevalence of HSV-2 infection in this sample was 44%. Compared to the reference standard, the sensitivity of the Meridian Diagnostics HSV-2 test was 95.5% (95% CI 83.3, 99.2) and specificity was 98.2% (95% CI 89.0, 99.9). The Focus Technologies test yielded 97.7% (95% CI 86.5, 99.9) sensitivity and 94.5% (95% CI 83.9, 98.6) specificity. CONCLUSIONS: The performance of these HSV-2 type-specific serologic assays was adequate to support their use in high prevalence populations, such as STD clinic patients.

Adolescent↗
PubMed2004

Corneal and epithelial thickness changes after 4 weeks of overnight corneal refractive therapy lens wear, measured with optical coherence tomography.

PURPOSE: To investigate thickness changes of the total cornea and epithelium across the horizontal corneal meridian after 4 weeks of overnight corneal refractive therapy (CRT) rigid contact lens (Paragon Vision Sciences, Mesa, AZ) wear. METHODS: Thirty subjects were fitted with CRT contact lenses (Dk/t = 67), which were worn overnight for 4 weeks. Corneal thickness was measured at nine locations along the horizontal meridian by using optical coherence tomography (OCT) before lens insertion in the evening. Corneal thickness was measured the next morning immediately after lens removal and 1, 3, 7, and 14 hours later. This was repeated on days 4, 10, and 28 of the study and then 3 days after discontinuing lens wear. RESULTS: Twenty-three subjects completed the study. At lens removal on day 1, the central and paracentral cornea swelled by 4.9% and 6.2%, respectively (both P = 0.000). The central epithelium thinned by 7.3%, and the mid peripheral epithelium thickened by 13% (both P = 0.000). Corneal swelling recovered throughout the day, with most of the deswelling taking place within the first 3 hours after lens removal. Maximal central epithelial thinning reached 13.5% by day 4. Three days after the study completion, corneal and epithelial thickness had recovered to baseline values. CONCLUSIONS: This study shows that CRT lenses induce differential overnight swelling across the cornea, with rapid deswelling during the day. Central epithelial thinning and paracentral thickening occurs, with recovery 3 days after discontinuation of lens wear.

Adult↗
PubMed2003

Effect of firefighter masks on monocular and binocular peripheral vision.

Peripheral vision can impact essential job functions of firefighters and other workers who use Self-Contained Breathing Apparatus and other full face masks. It is important for physicians to know how these masks alter peripheral vision. Also, one must understand the effect of monocular vision on peripheral vision. Using the Goldman Perimeter Machine we measured peripheral vision in the monocular and binocular state, with and without two different types of masks. The results show that monocularity causes an average loss of 23 degrees in the nasal meridian. The use of the masks did not affect this difference. Also, the masks caused an average loss of 28 degrees of peripheral vision in the inferior meridian. How these losses affect the ability of the users of the masks to perform their essential job functions still needs to be researched.

Adult↗
PubMed2006

Evaluation of four different fecal tests for determination of cure after Helicobacter pylori treatment.

BACKGROUND: Data evaluating the monoclonal tests for determination of cure after Helicobacter pylori treatment are scarce. GOALS: This study was aimed to evaluate the usefulness of 4 stool tests-2 new RAPID monoclonal immunochromatographic tests (RAPID Hp StAR, DakoCytomation, Cambridge, UK and ImmunoCard STAT! HpSA, Meridian Diagnostics, Cincinnati, OH) a monoclonal EIA test (Amplified IDEIA Hp StAR, DakoCytomation, Cambridge, UK), and a polyclonal EIA test (Premier Platinum HpSA, Meridian Diagnostics, Cincinnati, OH)-to confirm cure of H. pylori infection after eradication treatment. STUDY: Ninety-seven patients who underwent eradication treatment were included. Cure of H. pylori infection was determined using 2 consecutive reference tests. Fecal tests were performed according to the specifications of the manufacturer. Sensitivity, specificity, and positive and negative predictive values were calculated. RESULTS: After H. pylori eradication, the RAPID Hp StAR test has a sensitivity of 73% for detecting persistent infection, a specificity of 96% to 98%, a positive predictive value of 73% to 80% and a negative predictive value of 96%. For ImmunoCard STAT! HpSA the corresponding values were 91%, 97%, 77%, and 99%, for Amplified IDEIA Hp StAR 73%, 97%, 73%, and 97%, and for Premier Platinum HpSA 91%, 79%, 35%, and 98%. CONCLUSIONS: All tests except Premier Platinum HpSA were highly accurate confirming eradication after treatment.

Aged↗
PubMed2007

Regional repeatability measures of corneal thickness: Orbscan II and ultrasound.

PURPOSE: To compare repeatability of the measures of corneal thickness obtained by slit-scanning light method (Orbscan II) with those obtained by an ultrasound pachymeter, with special interest in the peripheral region of the cornea. METHODS: On 24 normal adults, aged 20 to 58 years (average 36 years) with up to -8.5 DS refractive error, three measures of corneal thickness were taken using Orbscan II and then by ultrasound pachymetry (under topical anesthesia with benoxinate 0.4%). The Orbscan central sample zone of 1 mm was selected, or the numerical maps were used to extract single point data along the horizontal corneal meridian to the nasal and temporal sides out to 4.5 mm. Ultrasound readings were taken from the central cornea and at the periphery just inside the limbus (4.5 mm from center) with a 2.4-mm diameter probe. RESULTS: For a central 1-mm diameter zone, the coefficient of variation (CV) for three consecutive corneal thickness measures was 0.81%+/-0.44%, but was marginally higher (p=0.004), if just the central single point data was taken with Orbscan (0.86%+/-0.45%). Similar repeatability was noted for the numerical output across the temporal side along the horizontal meridian out to 2.5 mm from the center, but farther out to 4 mm and on the nasal side the repeatability was slightly less and around 1.0% (p<0.001). Orbscan point readings of thickness could only sometimes be obtained at 4.5 mm temporally (with a poorer CV of 1.32%) and very rarely at 4.5 mm on the nasal side. No absolute differences in Orbscan repeatability were noted when comparing emmetropic with myopic subjects (p>or=0.5). Ultrasound pachymetry readings across the central zone were repeatable to 0.82%+/-0.67%. When measured with the edge of the ultrasound probe just touching the limbus, the repeatability of ultrasound readings was 1.37%+/-1.10% temporally and 1.49%+/-1.02% nasally, but neither was statistically worse that the most peripheral readings for Orbscan (p>or=0.210). However, it was also noted that the absolute values of corneal thickness, even with the application of the 0.92 acoustic factor, were 0.010 mm greater for Orbscan at the center and 0.040 mm in the corneal periphery. CONCLUSIONS: Orbscan II provides the clinician with a repeatable noninvasive method of measuring corneal thickness that is not necessarily any better than ultrasound pachymetry, and should not be considered as interchangeable with that for ultrasound.

Adult↗
PubMed1983

The basal dendrites of Meynert cells in the striate cortex of the monkey.

A study has been made of the basal dendrites of Meynert cells in the striate cortex of the macaque monkey in sections parallel to the pial surface impregnated by the Golgi technique. The longest basal dendrite observed extended up to 0.6 mm and the average length of the longest dendrite on each cell was about 0.28 mm. In general, the dendritic field was in the form of an ellipse with mean major and minor axes of 0.22 mm and 0.11 mm respectively, and encompassing an area of about 0.13 mm2. The directions of the major axes were perpendicular to the lunate sulcus in the sections adjacent to the lunate sulcus, and parallel to the horizontal meridian in sections taken from the region of the representation of the meridian, suggesting that the basal dendritic fields are orientated in parallel with the directions of the ocular dominance bands.

Animals↗
PubMed2004

Non-invasive diagnosis of Helicobacter pylori infection in adult dyspeptic patients by stool antigen detection: does the rapid immunochromatography test provide a reliable alternative to conventional ELISA kits?

Stool antigen-testing allows non-invasive detection of Helicobacter pylori that is indicative of active infection. Three commercial kits are currently marketed in the UK for stool antigen-testing. The aim of this study was to conduct a comparative evaluation of the performances of each of these tests, compared with culture and histological examination of gastric biopsies, for pre-treatment diagnosis of infection in an adult dyspeptic population in south-east England. Examination of 112 stool samples by the Premier Platinum HpSA ELISA (Meridian Diagnostics) and by the Amplified IDEIA HpStAR ELISA (DakoCytomation) kits demonstrated that the latter was more sensitive (81.3 versus 93.8%, respectively) and specific (91.7 versus 100.0%, respectively). Additionally, the IDEIA HpStAR was easier to interpret, with OD readings of positive and negative results being far from the recommended cut-off, whereas equivocal results that were generated by the HpSA kit were difficult to interpret. Additional testing of 87 of the 112 stools by the ImmunoCard STAT! HpSA kit (Meridian Diagnostics) demonstrated that this test was easier to perform than ELISA and was more sensitive than the HpSA kit but, compared with the IDEIA HpStAR kit, the ImmunoCard test was less sensitive (87.8 versus 95.9%, respectively) and specific (89.4 versus 100.0%, respectively). Furthermore, the ImmunoCard test generated weakly positive results, correlating with lower OD readings for both ELISA kits, that were difficult to interpret. The Amplified IDEIA HpStAR kit is therefore the most sensitive and specific of the three tests that are available for pre-treatment, non-invasive detection of H. pylori in stool samples in an English adult dyspeptic population.

Adult↗
PubMed2002

Is the superior cornea continuously swollen?

BACKGROUND: During waking hours, the upper eyelid typically covers the superior two millimetres of the cornea. This partial oxygen barrier is the presumed cause of the reversibly elevated epithelial oxygen uptake in this region of the cornea. We studied the thickness profile of the vertical corneal meridian before and after extended exposure to a uniform hypoxic stimulus to ascertain the extent of chronic superior corneal swelling that might be attributable to coverage by the upper lid. METHODS: Each of 16 male subjects, age 24 to 40 years, wore a uniformly thick polymacon lens (Dk/L = 5.7 x 10-9 cm ml O2/s ml mmHg) on one eye for four hours with the eyelid patched. Thickness was measured at five sites across the vertical corneal meridian prior to and immediately after patching. Baseline thickness and swelling were compared at the superior and inferior edges of selected central chord diameters. RESULTS: At baseline, the superior cornea was, on average, 31 mm thicker (p = 0.0002) at the 7.1 mm chord and 9 mm thicker (not significant) at the 3.75 mm chord, compared to the inferior cornea at the corresponding chords. Mean corneal swelling ranged from 70.5 mm centrally to approximately 48 mm at the 7.1 mm chord diameter. The extent of swelling at the corresponding superior and inferior sites was virtually identical for both chord diameters. CONCLUSION: Although the superior cornea is significantly thicker than the inferior cornea, this difference does not appear to be immediately related to the chronic differences in open eye oxygen tension between the superior and inferior regions.

Adult↗
PubMed2003

The pattern of ocular dominance columns in cat primary visual cortex: intra- and interindividual variability of column spacing and its dependence on genetic background.

We present a comprehensive analysis of the intrinsic variability of the periodicity of ocular dominance columns in cat primary visual cortex (area 17) and its relationship to genetic background and visual experience. We characterized the intra-areal and interindividual variability of column spacing in a large set (n = 49) of ocular dominance patterns adapting a recently developed technique for the two-dimensional analysis of orientation column patterns. Patterns were obtained from three different cat colonies (termed F, M and D), the cats having either normal visual experience or experimentally induced strabismus. Two-dimensional maps of local column spacing were calculated for every pattern. In individual cortices, local column spacings varied by > 50% with the majority of column spacings ranging between 0.6 and 1.5 mm in different animals. In animals from colonies F and M (n = 29), the mean column spacing ranged between 1.03 and 1.27 mm and exhibited no significant differences, either between the two breeds or between strabismic and normal animals. The mean spacing was moderately clustered in the left and right brain hemisphere of individual animals but not in littermates. In animals from colony D (n = 2), average column spacing ranged between 0.73 and 0.95 mm, and was thus significantly different from the distribution of spacings in animals from breeds F and M, suggesting an influence of genetic factors on the layout of ocular dominance columns. Local column spacing exhibited a considerable systematic intra-areal variation, with largest spacings along the representation of the horizontal meridian and smallest spacings along the peripheral representation of the vertical meridian. The total variability of ocular dominance column spacing comprised 24% systematic intra-areal variation, 18% interindividual differences of mean column spacing and 58% nonsystematic intra-areal variability.

Animals↗