Andrew Whatham

Influence of accommodation on off-axis refractive errors in myopic eyes

INTRODUCTION This study aims to understand off-axis refraction during accommodation and to identify whether the relative hyperopia generally observed in myopic eyes changes with accommodation. METHOD Twenty bilateral myopes (18 to 33 years) between -0.50 D and -4.25 D (spherical equivalent) and astigmatism less than 1.25 D participated in this study. A soft contact lens was used to correct refractive error for all measurements. Non-cycloplegic autorefraction was measured at the fovea and 20 degrees, 30 degrees, and 40 degrees eccentricities in the nasal and temporal retina at distances of 2 m, 40 cm, and 30 cm. RESULTS Peripheral refractive error, relative to central refraction, became less hyperopic with increasing eccentricity and with increasing accommodation. Lag of accommodation increased with accommodation (p < 0.001) shifting the image-shell backward relative to the retina. In the farther periphery, there was either no change in refractive error or increased myopic shifts with accommodation. Astigmatism increased with eccentricity and significantly increased in the farther eccentricities with accommodation (p < 0.001). CONCLUSION Myopes display hyperopic shifts in the center and near peripheral field during near-viewing, while the farther periphery either remains unshifted or demonstrates a myopic shift. These results are due to the combined effect of lag of accommodation and an increased curvature of field during accommodation.

Vitamin and mineral deficiencies in the developed world and their effect on the eye and vision.

Vitamin and mineral deficiencies are common in developing countries, but also occur in developed countries. We review micronutrient deficiencies for the major vitamins A, cobalamin (B12), biotin (vitamin H), vitamins C and E, as well as the minerals iron, and zinc, in the developed world, in terms of their relationship to systemic health and any resulting ocular disease and/or visual dysfunction. A knowledge of these effects is important as individuals with consequent poor ocular health and reduced visual function may present for ophthalmic care.

The usefulness of multimodal imaging for differentiating pseudopapilloedema and true swelling of the optic nerve head: a review and case series

Ophthalmic practitioners have to make a critical differential diagnosis in cases of an elevated optic nerve head. They have to discriminate between pseudopapilloedema (benign elevation of the optic nerve head) and true swelling of the optic nerve head. This decision has significant implications for appropriate patient management. Assessment of the optic disc prior to the advanced imaging techniques that are available today (particularly spectral domain optical coherence tomography and fundus autofluorescence), has mainly used diagnostic tools, such as funduscopy and retinal photography. As these traditional methods rely on the subjective assessment by the clinician, evaluation of the elevated optic nerve head to differentiate pseudopapilloedema from true swelling of the optic nerve head can be a challenge in clinical practice with patients typically referred for further neuroimaging investigation when the diagnosis is uncertain. The use of multimodal ocular imaging tools such as spectral domain optical coherence tomography, short wavelength fundus autofluorescence and ultrasonography, can potentially aid in the differentiation of pseudopapilloedema from true swelling of the optic nerve head, in conjunction with other clinical findings. By doing so, unnecessary patient costs and anxiety in the case of pseudopapilloedema can be reduced, and appropriate urgent referral and management in the case of true swelling of the optic nerve head can be initiated.Ophthalmic practitioners have to make a critical differential diagnosis in cases of an elevated optic nerve head. They have to discriminate between pseudopapilloedema (benign elevation of the optic nerve head) and true swelling of the optic nerve head. This decision has significant implications for appropriate patient management. Assessment of the optic disc prior to the advanced imaging techniques that are available today (particularly spectral domain optical coherence tomography and fundus autofluorescence), has mainly used diagnostic tools, such as funduscopy and retinal photography. As these traditional methods rely on the subjective assessment by the clinician, evaluation of the elevated optic nerve head to differentiate pseudopapilloedema from true swelling of the optic nerve head can be a challenge in clinical practice with patients typically referred for further neuroimaging investigation when the diagnosis is uncertain. The use of multimodal ocular imaging tools such as spectral domain optical coherence tomography, short wavelength fundus autofluorescence and ultrasonography, can potentially aid in the differentiation of pseudopapilloedema from true swelling of the optic nerve head, in conjunction with other clinical findings. By doing so, unnecessary patient costs and anxiety in the case of pseudopapilloedema can be reduced, and appropriate urgent referral and management in the case of true swelling of the optic nerve head can be initiated.

Sildenafil alters retinal function in mouse carriers of retinitis pigmentosa.

Sildenafil, the active ingredient in Viagra, has been reported to cause transient visual disturbance from inhibition of phosphodiesterase 6 (PDE6), a key enzyme in the visual phototransduction pathway. This study investigated the effects of sildenafil on the rd1(+/-) mouse, a model for carriers of Retinitis Pigmentosa which exhibit normal vision but may have a lower threshold for cellular stress caused by sildenafil due to a heterozygous mutation in PDE6. Sildenafil caused a dose-dependent decrease in electroretinogram (ERG) responses of normal mice which mostly recovered two days post administration. In contrast, rd1(+/-) mice exhibited a significantly reduced photoreceptor and a supernormal bipolar cell response to sildenafil within 1 h of treatment. Carrier mice retinae took two weeks to return to baseline levels suggesting sildenafil has direct effects on both the inner and outer retina and these effects differ significantly between normal and carrier mice. Anatomically, an increase in expression of the early apoptotic marker, cytochrome C in rd1(+/-) mice indicated that the effects of sildenafil on visual function may lead to degeneration. The results of this study are significant considering approximately 1 in 50 people are likely to be carriers of recessive traits leading to retinal degeneration.

The value of clinical electrophysiology in the assessment of the eye and visual system in the era of advanced imaging

Electrophysiological techniques allow clinical investigations to include a ‘dissection’ of the visual system. Using suitable electrophysiological techniques, the ‘dissection’ allows function to be ascribed to the different photoreceptors (rod and cone photoreceptors), retinal layers, retinal location or the visual pathway up to the visual cortex. Combined with advances in genetics, retinal biochemistry, visual fields and ocular imaging, it is now possible to obtain a better understanding of diseases affecting the retina and visual pathways. This paper reviews core electrophysiological principles that can complement other examination techniques, including advanced ocular imaging, and help the interpretation of other clinical data and thus, refine and guide clinical diagnosis.

Reading strategies in Stargardt's disease with foveal sparing

BackgroundSubjects with a ring scotoma can use two retinal loci, a foveal and a peripheral, for reading. Our aim was to investigate the relative use of both retinal loci as a function of the spared foveal area size and the spatial resolution at both retinal loci.FindingsTwo patients with Stargardts disease and ring scotomas read through a scanning laser ophthalmoscope a series of letters and words at various character sizes. The number of fixations made using each retinal locus was quantified. The relative use of each retinal locus depended on character size of the stimulus. Both patients used exclusively the eccentric retinal locus to read words of large character sizes. At small character sizes, the central retinal locus was predominantly used. For reading letters or words, once foveal fixation was used, patients did not shift back to the eccentric retinal locus. When spatial resolution allowed deciphering at both the eccentric and the central areas, patients consistently fixated with the eccentric retinal locus.ConclusionsSpatial resolution at the eccentric locus appears as a determinant factor to select the retinal area for reading. Reading strategies in patients with Stargardts disease and a ring scotoma demonstrate a pattern of coordination of both eccentric and central retinal loci, reflecting a high degree of adaptation.

Change in peripheral refraction and curvature of field of the human eye with accommodation

Recent research showed that the peripheral refractive state is a sufficient stimulus for myopia progression. This finding led to the suggestion that devices that control peripheral refraction may be efficacious in controlling myopia progression. This study aims to understand whether the optical effect of such devices may be affected by near focus. In particular, we seek to understand the influence of accommodation on peripheral refraction and curvature of field of the eye. Refraction was measured in twenty young subjects using an autorefractor at 0° (i.e. along visual axis), and 20°, 30° and 40° field angles both nasal and temporal to the visual axis. All measurements were conducted at 2.5 m, 40 cm and 30 cm viewing distances. Refractive errors were corrected using a soft contact lens during all measurements. As field angle increased, refraction became less hyperopic. Peripheral refraction also became less hyperopic at nearer viewing distances (i.e. with increasing accommodation). Astigmatism (J180) increased with field angle as well as with accommodation. Adopting a third-order aberration theory approach, the position of the Petzval surface relative to the retinal surface was estimated by considering the relative peripheral refractive error (RPRE) and J180 terms of peripheral refraction. Results for the estimated dioptric position of the Petzval surface relative to the retina showed substantial asymmetry. While temporal field tended to agree with theoretical predictions, nasal response departed dramatically from the model eye predictions. With increasing accommodation, peripheral refraction becomes less hyperopic while the Petzval surface showed asymmetry in its change in position. The change in the optical components (i.e. cornea and/or lens as opposed to retinal shape or position) is implicated as at least one of the contributors of this shift in peripheral refraction during accommodation.

Imaging into the future of optometric practice.

Digital imaging of the anterior and/or posterior segment of the eye has found its way into many optometric practices over the past few years in particular. Increased use of slitlamp and fundus cameras has been due, at least in part, to optometrists feeling comfortable in charging for these services in addition to an eye examination covered under Medicare. Some optometrists are already using optical coherence tomography (OCT) to view the anterior (Visante) and posterior (Stratus, Cirrus, RTVue, Topcon 3D, Copernicus, Spectralis) segments to obtain cross-sectional and three-dimensional (3-D) images of the retina with high depth resolution (better than 10 mm), a GDx for measuring the circumpapillary thickness profile of the retinal nerve fibre layer or a Heidelberg Retina Tomograph (HRT) to image the optic disc and surroundings using confocal scanning laser ophthalmoscopy. The use of ocular imaging in optometric practices is unlikely to stop there, if the amount and nature of current imaging research are considered. The accompanying graph (Figure 1) shows the rise in OCT retinal imaging publications appearing in the online searchable database Medline from 2000 to 2007. The increasing interest in advancing retinal imaging techniques was also reflected at this year’s ARVO (Association for Research in Vision and Ophthalmology) meeting in Fort Lauderdale, Florida, which was held from 25 April to 1 May 2008, and by a special satellite meeting dedicated to ocular imaging held on 25–26 April. This was the sixth meeting of the International Society for Imaging in the Eye (ISIE), yet the first incorporated into the ARVO meeting. Abstracts from the 6th ISIE meeting at ARVO 2008 can be accessed online through: http://www.arvo.org/isie/. Within this session and other plenary sessions on imaging during the meeting proper, new approaches, instrumentation and methods were introduced to the scientific community. The following discussion will concentrate on posterior segment imaging, which featured heavily at the ARVO meeting. It is noteworthy to say that important findings were also reported Publication year P ub lic at io ns p er y ea r

Reconciling visual field defects and retinal nerve fibre layer asymmetric patterns in retrograde degeneration: an extended case series

Accurate diagnosis in patients presenting with lesions at various locations within the visual pathway is challenging. This study investigated functional and structural changes secondary to such lesions to identify patterns useful to guide early and effective management.