Peter G. Swann

Age-related changes in optical and biometric characteristics of emmetropic eyes

We measured optical and biometric parameters of emmetropic eyes as a function of age. There were approximately 20 subjects each in age groups 18-29, 30-39, 40-49, 50-59, and 60-69 years with similar male and female numbers. One eye was tested for each subject, having spherical equivalent in the range -0.88 D to +0.75 D and <or=0.50 D astigmatism. Despite considerable data scatter, we found significant age changes: anterior chamber depth decreased 0.011 mm/year, lens central thickness increased 0.024 mm/year, anterior segment depth increased 0.013 mm/year, eye length increased 0.011 mm/year, anterior lens radius of curvature decreased 0.044 mm/year, and lens equivalent refractive index decreased 0.0003/year. Males had higher anterior corneal radii of curvature (0.16 mm), lower lens equivalent refractive index (0.006), longer vitreous lengths (0.51 mm), and longer axial lengths (0.62 mm) than females. Superficially, the results suggest that eyes get bigger as they age. However, results can be related to refraction patterns in which refraction is stable in 20s to 40s and then moves in the hypermetropic direction. It is likely that several young subjects will become hypermetropic as they age, and it is possible that some of the older subjects were myopic when younger.

Cone-mediated multifocal electroretinogram in early age-related maculopathy and its relationships with subjective macular function tests

Purpose. To investigate the multifocal electroretinogram (mfERG) and subjective function in early age-related maculopathy (ARM). Methods. Seventeen subjects with early ARM with visual acuity (VA) of 6/12 or better and 20 age-matched control subjects were examined. We assessed mfERGs, high and low contrast distance VA, near VA, low luminance VA, contrast sensitivity, saturated and desaturated Panel D-15 and visual fields (mean sensitivity). The mfERG responses were analysed by comparing central-overall (method 1) and superior-inferior (method 2) ratios. Results. The mfERG did not discriminate between the groups whereas colour vision (tritan deficiency), contrast sensitivity, and high contrast and low contrast VA showed significantly reduced responses for the early ARM group compared with the control group (p ≤⃒ 0.01). The mfERG first-order kernel responses correlated significantly with the desaturated D-15 in both methods (r = −0.5, p ≤⃒ 0.05). Fundus grading was not correlated with the mfERG measures. Conclusions. Although the mfERG correlated significantly with the desaturated D-15 in early ARM, suggesting it operates at a sensitive level, it failed to discriminate between the control and ARM groups. In our sample, the subjective function measures were more sensitive than the mfERG measures.

Cone- and rod-mediated multifocal electroretinogram in early age-related maculopathy

PurposeTo investigate the cone- and rod-mediated multifocal electroretinograms (mfERG) in early age-related maculopathy (early ARM).Methods and subjectsWe investigated the cone- and rod-mediated mfERG in 17 eyes of 17 subjects with early ARM and 16 eyes of 16 age-matched control subjects with normal fundi. All subjects had a visual acuity of 6/12 or better. We divided the ARM subjects into two groups based on drusen size and retinal pigment epithelium abnormalities—a less advanced (ARM1) and a more advanced (ARM2) group. The mfERG data were compared to templates derived from the control group. We analysed the mfERG results for the central and peripheral fields (CP method) and the superior and inferior fields (SI method).ResultsWhile the mean cone results showed no statistically significant difference between the groups, the rods showed significantly delayed responses in the ARM1 group for the CP and the SI methods, but not in the ARM2 group, although there was a trend of longer latencies compared to the control group.ConclusionOur results show a functional impairment of the rods in early ARM subjects. As there is histopathological evidence showing earlier rod than cone impairment in early ARM, following the rod function with the mfERG might be helpful in diagnosis or for monitoring the progression of early ARM.

Monitoring retinal function in early age-related maculopathy: visual performance after 1 year

PurposeTo monitor visual performance in early age-related maculopathy (ARM).MethodsWe measured monocular visual function—high-contrast visual acuity (HC-VA), central visual fields (mean sensitivity, MS), colour vision (desaturated Panel D-15), Pelli–Robson (P–R), and cone- and rod-mediated multifocal electroretinograms (mfERG) in 13 ARM subjects and 13 age-matched control subjects with normal fundi at baseline and after 1 year. All had visual acuity of 6/12 or better. The mfERG data were compared to templates derived from the control group at baseline. We analysed the mfERG results by averaging the central and peripheral fields and the superior and inferior fields (CP and SI methods) and by calculating the local responses.ResultsThe mean rod-mediated responses were significantly delayed in the ARM group for the CP (P=0.04) and the SI methods (P=0.03) at baseline compared to the control group. This did not change significantly after 1 year, whereas the mean cone-mediated responses were within the normal range at both times. Although the local analysis revealed lower amplitudes for the cone- and rod-mediated responses at baseline this was not found after 1 year and only the local rod-mediated latencies were delayed at both times (P<0.01). HC-VA, desaturated Panel D-15 and P–R were significantly worse in the ARM group (P⩽0.01) at baseline but did not show further significant deterioration. Progressive fundus changes were found in only two subjects (18%).ConclusionAlthough there was significant impairment of retinal function in early ARM at baseline no further deterioration was evident after 1 year.

Investigation of parameters influencing intraocular pressure increases during sleep

In previous studies, we have observed that young normal subjects show an increase in intraocular pressure (IOP) after sleep. Here we describe three experiments which investigated: (i) the effects of sleep in five groups of subjects: glaucoma, suspect glaucoma, young high‐normal IOP, old high‐normal IOP groups and an elderly control group, (ii) the effect of exposure to bright light (2500 lux) during sleep on associated IOP changes, and (iii) the relationship between changes in IOP and plasma melatonin during sleep, For all experiments IOP was measured before and after sleep. We found that IOP increased significantly after sleep. There was also a significant difference between the five groups with the old high‐normal group showing the greatest increase, and the young high‐normal group showing the lowest increase in IOP. The increase in IOP after sleep was reduced when the same subjects slept in bright light compared to that recorded when subjects slept in the dark. Plasma melatonin levels, as well as IOP, increased after sleep in the dark although there was no correlation between these changes for individual subjects.

Age-related maculopathy. II: The nature of the central visual field loss.

This is the second of three papers dealing with age‐related maculopathy (ARM) and its effects on visual function (Swann, P. G. and Lovie‐Kitchin. J. E. Age‐related maculopathy. I: A review of its morphology and effects on visual function. Ophthal. Physiol. Opt.10, 149–158 (1990)). We investigated the nature or character of the central visual field loss in ARM and pre‐age related maculopathy (FARM) and compared them with age‐mulched normal subjects. Central visual fields were examined using the Friedmann Visual Field Analyser. Mark II, the Bausch and Lomb Autoplot Tangent Screen and Amsler charts. The central visual field defects in ARM were predominantly paracentral with a relative sparing of foveal sensitivity. PARM subjects did not show significant visual field defects. However, three FARM subjects did show slight distortions with the Amsler charts. The third paper in this series will compare the efficacy of the three methods of visual field investigation in the detection of these defects.

The Rod-Mediated Multifocal Electroretinogram in Aging and in Early Age-Related Maculopathy

Purpose: To measure function with the rod-mediated multifocal electroretinogram (mfERG) in younger and older subjects with normal vision and with early age-related maculopathy (ARM). Methods: Thirty subjects were studied: 10 healthy subjects with a mean age of 31 years (young group), 10 healthy subjects with a mean age of 71 years (old group), and 10 early ARM subjects with a mean age of 71 years (early ARM group). The influence of cataract was approximated by retesting five subjects of the young group through an 0.3 neutral density filter (ND filter group). We analyzed first-order N1P1-amplitude and P1-implicit time (P1-IT) mfERG responses and correlated them with funduscopic changes as defined by the Age-Related Eye Disease Study (AREDS) group. Results: Averaged concentric ring P1-ITs were significantly delayed in the old (p = 0.02) and early ARM (p < 0.001) compared with the young group and in the early ARM group compared with the old and ND group (p ≤ 0.01). There were no significant differences in N1P1-amplitudes between groups, but there was a significant location effect for all groups with highest mean amplitudes for the most peripheral ring of hexagons (p < 0.01). Significantly delayed overall P1-ITs (p < 0.05) were correlated with progressive funduscopic changes. Conclusions: Aging and early ARM affects the rod-mediated mfERG, and there is good correlation with funduscopic changes. Although a lens effect cannot be excluded, a neuronal transmission alteration at the postreceptoral level is suggested.

Fluctuations in intra-ocular pressure with sleep:I. Time course of IOP increase after the onset of sleep

Ten normal subjects slept over a series of four nights for time periods of 30 minutes, 1, 2 and 4 hours. Intra‐ocular pressure (IOP) measurements were made using a non‐contact tonometer before and after sleep. The subjects showed a significant increase in IOP of 3.45 mm Hg after 30 minutes of sleep and a further IOP increase thereafter to 6.41 mm Hg above baseline. Such increases in IOP after sleep in normal subjects suggest that glaucoma patients and those suspected of having glaucoma should be monitored overnight to assess their IOP control mechanisms.

The detection of diabetic retinopathy by Australian optometrists

Background: Diabetes mellitus is a systemic disease affecting approximately 750,000 Australians of whom more than 70,000 are Queenslanders. It can have serious ocular consequences and patients with diabetes require regular eye examinations to determine the degree of ocular involvement and the stage of retinopathy, if present. It is important that optometrists detect diabetic retinal changes and refer appropriately. We sought to determine the proficiency of optometrists at detecting retinal changes caused by diabetes.

Age-related maculopathy. I: A review of its morphology and effects on visual function.

Age‐related maculopathy (ARM) is a leading cause of permanent vision loss in elderly people. ARM therefore constitutes an important public health problem which will increase in magnitude as the number of aged people in the general population becomes greater. The consequences of this condition are exacerbated by the fact that treatment, especially of the atrophic form of the disease, is ineffective. While laser photocoagulation may be helpful in the exudative form of ARM, there is often an inexorable progression towards severe vision loss in these patients. Therefore considerable attention needs to be paid to the aetiology of ARM, the potential for its prevention or delayed onset and its recognition through functional disturbances. This is the first of three papers dealing with ARM and its effects on visual function. We review its morphology and the visual disturbances that may ensue. The second and third papers will discuss the nature and detection of the central visual field loss due to ARM.