Ian Pacey | University of Bradford (original) (raw)

Papers by Ian Pacey

Investigative Ophthalmology & Visual Science, 2008

European Journal of Ophthalmology, 2019

Background/objectives: There is a significant variation in the way neovascular age-related macula... more Background/objectives: There is a significant variation in the way neovascular age-related macular degeneration patients respond to anti–vascular endothelial growth factor treatment. Both the financial and time cost of treatment are significant. As such, being able to predict patient response to treatment is valuable. Subjects/methods: 72 eyes treated with intravitreal aflibercept were retrospectively included in analysis. For each subject, visual acuity (letters) and central retinal thickness (µm) at baseline, second, third and fourth visits, as well as 12-month visits, were collated; a plot of visual acuity versus time was generated and a slope of the first three (slope3) and first four (slope4) visits was calculated. Differences in visual acuity at each visit compared to baseline were determined, as well as percentage differences in central retinal thickness at each visit compared to baseline. Lesion sub-type and the presence of fluid and haemorrhage were also recorded. Results: ...

Investigative ophthalmology & visual science, 2015

Reduced binocularity is a prominent feature of amblyopia and binocular cues are thought to be imp... more Reduced binocularity is a prominent feature of amblyopia and binocular cues are thought to be important for prehension. We examine prehension in individuals with amblyopia when the target-object was flanked, thus mimicking everyday prehension. Amblyopes (n = 20, 36.4 ± 11.7 years; 6 anisometropic, 3 strabismic, 11 mixed) and visually-healthy controls (n = 20, 27.5 ± 6.3 years) reached forward, grasped, and lifted a cylindrical target-object that was flanked with objects either (lateral) side of the target, or in front and behind it in depth. Only six amblyopes (30%) had measurable stereoacuity. Trials were completed in binocular and monocular viewing, using the better eye in amblyopic participants. Compared with visual normals, amblyopes displayed a longer overall movement time (P = 0.031), lower average reach velocity (P = 0.021), smaller maximum aperture (P = 0.007), and a longer duration between object contact and lift (P = 0.003). Differences between groups were more apparent wh...

Investigative ophthalmology & visual science, 1999

To determine the within-visit between-algorithm and the within-algorithm between-visit difference... more To determine the within-visit between-algorithm and the within-algorithm between-visit differences in sensitivity for the SITA Standard, SITA Fast, FASTPAC, and Full Threshold algorithms in stable primary open angle glaucoma. One designated eye from each of 29 patients (age 67.3 +/- 10.2 years; mean +/- SD) experienced in automated perimetry was examined with the four algorithms on each of three visits, using the Humphrey Field Analyzer 750 and Program 30-2. The group mean Mean Sensitivity was 1.0 dB greater for SITA Standard than Full Threshold (P < 0.001), 0.7 dB greater for SITA Standard than FASTPAC (P < 0.001), 1.6 dB greater for SITA Fast than FASTPAC (P < 0.001), and 0.9 dB greater for SITA Fast than SITA Standard (P < 0.001). The higher pointwise sensitivity for SITA Fast compared to Full Threshold, FASTPAC, and SITA Standard increased with increase in defect depth. The examination duration for SITA Standard was 53% of that for Full Threshold and 50% shorter for ...

Investigative ophthalmology & visual science, 1999

To determine the between-algorithm differences in perimetric sensitivity for the Swedish Interact... more To determine the between-algorithm differences in perimetric sensitivity for the Swedish Interactive Threshold algorithm (SITA) Standard, SITA Fast, FASTPAC, and Full Threshold algorithms; to determine the between-subject, between-algorithm differences in the magnitude of the normal variation in sensitivity. The sample comprised 50 normal subjects (mean age, 52.9 +/- 18.5 years) experienced in automated perimetry. One randomly assigned eye was examined at three visits with Program 30-2 of the Humphrey Field Analyzer (HFA). The first visit was a familiarization session. A two-period crossover design with order randomization within visits was used over the second and third visits. SITA Standard, SITA Fast, and HFA 640 Full Threshold were administered during one visit. FASTPAC and HFA 750 Full Threshold were administered during the remaining visit. Group mean Mean Sensitivity was 0.8 dB higher for SITA Standard than for Full Threshold (P < 0.001) and 1.3 dB higher for SITA Fast than...

Investigative ophthalmology & visual science, 1998

To determine the intraindividual and interindividual characteristics of normal sensitivity derive... more To determine the intraindividual and interindividual characteristics of normal sensitivity derived by short-wavelength automated perimetry (SWAP) as a function of threshold algorithm. To determine also the influence of ocular media absorption on the magnitude of the interindividual variation in normal sensitivity, and hence the confidence limits, derived by SWAP. The sample comprised 51 normal subjects, stratified for age by decade (mean age, 55.5 years; range, 24-83 years) and experienced in white-on-white (W-W) perimetry and SWAP. One randomly assigned eye of each subject was examined on three occasions with Program 30-2 of the 640 Humphrey Field Analyzer using the Full Threshold and FASTPAC strategies for SWAP and W-W perimetries. Ocular media absorption (OMA) was assessed by the difference in scotopic sensitivity to stimuli of 410 and 560 nm. The group mean examination time (P < 0.001) was greater for SWAP than for W-W perimetry for both the Full Threshold (15.0% longer) and ...

Aim: To evaluate repeatability and reproducibility of macular thickness measurements in visually ... more Aim: To evaluate repeatability and reproducibility of macular thickness measurements in visually normal eyes using the Topcon 3D OCT-1000. Methods: Phase 1 investigated scan repeatability, the effect of age and pupil dilation. Two groups (6 younger and 6 older participants) had one eye scanned 5 times pre and post-dilation by 1 operator. Phase 2 investigated between-operator, within and between-visit reproducibility. 10 participants had 1 un-dilated eye scanned 3 times on 2 separate visits by 2 operators. Results: Phase 1: No significant difference existed between repeat scans (p=0.75) and no significant difference was found pre-and post-dilation (p=0.54). In the younger group variation was low (95% limits ± 3.62 m) and comparable across all retinal regions. The older group demonstrated greater variation (95% limits ± 7.6 m). Phase 2: For a given retinal location, 95% confidence limits for within-operator, within-visit reproducibility was 5.16 m. This value increased to 5.56 m for the same operator over two visits and to 6.18 m for two operators over two visits. Conclusion: A high level repeatability, close to 6 m, of macular thickness measurement is possible using the 3D OCT-1000. Measured differences in macular thickness between successive visits that exceed 6 m in pre-presbyopic individuals are therefore likely to reflect actual structural change. OCT measures are more variable in older individuals and it is advisable to take a series of scans so that outliers can be more easily identified.

Ophthalmic and Physiological Optics, 1997

PLoS ONE, 2013

Background: Adults with amblyopia ('lazy eye'), long-standing strabismus (ocular misalignment) or... more Background: Adults with amblyopia ('lazy eye'), long-standing strabismus (ocular misalignment) or both typically do not experience visual symptoms because the signal from weaker eye is given less weight than the signal from its fellow. Here we examine the contribution of the weaker eye of individuals with strabismus and amblyopia with both eyes open and with the deviating eye in its anomalous motor position. Methodology/Results: The task consisted of a blue-on-yellow detection task along a horizontal line across the central 50 degrees of the visual field. We compare the results obtained in ten individuals with strabismic amblyopia with ten visual normals. At each field location in each participant, we examined how the sensitivity exhibited under binocular conditions compared with sensitivity from four predictions, (i) a model of binocular summation, (ii) the average of the monocular sensitivities, (iii) dominant-eye sensitivity or (iv) non-dominant-eye sensitivity. The proportion of field locations for which the binocular summation model provided the best description of binocular sensitivity was similar in normals (50.6%) and amblyopes (48.2%). Average monocular sensitivity matched binocular sensitivity in 14.1% of amblyopes' field locations compared to 8.8% of normals'. Dominant-eye sensitivity explained sensitivity at 27.1% of field locations in amblyopes but 21.2% in normals. Non-dominant-eye sensitivity explained sensitivity at 10.6% of field locations in amblyopes but 19.4% in normals. Binocular summation provided the best description of the sensitivity profile in 6/10 amblyopes compared to 7/10 of normals. In three amblyopes, dominant-eye sensitivity most closely reflected binocular sensitivity (compared to two normals) and in the remaining amblyope, binocular sensitivity approximated to an average of the monocular sensitivities. Conclusions: Our results suggest a strong positive contribution in habitual viewing from the non-dominant eye in strabismic amblyopes. This is consistent with evidence from other sources that binocular mechanisms are frequently intact in strabismic and amblyopic individuals.

Ophthalmology, 2013

To examine foveal structure in amblyopia using spectral-domain optical coherence tomography (SD-O... more To examine foveal structure in amblyopia using spectral-domain optical coherence tomography (SD-OCT). Prospective, cross-sectional study. Two subject groups were recruited to the study: 85 amblyopes (34 adults, 51 children) and 110 visually normal controls (44 adults, 66 children). A detailed eye examination, including an SD-OCT scan, was performed in all participants. A total of 390 eyes of 195 subjects were imaged using a 3-dimensional (3D) macula scan covering a nominal 6 × 6-mm area with a resolution of 256 × 256 (65,536 axial scans). Data from the B-scans bisecting the fovea both horizontally and vertically were fitted with a mathematical model of the fovea to determine a range of foveal parameters. Foveal thickness, foveal pit depth, and foveal pit slope. Bilateral differences between the eyes of amblyopes compared with visually normal controls were found. The difference between foveal structure in amblyopic participants relative to structure in subjects with normal vision persisted even when variables such as age, ethnicity, axial length, and sex were taken into account. Amblyopes showed increased foveal thickness (+8.31 μm; P = 0.006) and a reduction in pit depth in the horizontal meridian (-10.06 μm; P = 0.005) but not in the vertical meridian (P = 0.082) when compared with subjects with normal vision. Foveal pit slopes were found to be approximately 1 degree flatter in the nasal (P = 0.033) and temporal (P = 0.014) meridians in amblyopes, but differences between amblyopes and controls in the superior (P = 0.061) and inferior (P = 0.087) meridians did not reach statistical significance. No statistically significant interocular differences were found in the foveal structure between amblyopic and fellow eyes. Differences were found in the foveal structure in both eyes of amblyopes compared with subjects with normal vision. These differences consisted of increased foveal thickness, reduced pit depth when measured along the horizontal meridian, and flattening of the nasal and temporal sides of the foveal pit.