Clinical utility of irx3 in keratoconus.

CLINICAL RELEVANCE: Diagnosis and monitoring of keratoconus is increasingly being conducted with the aid of imaging equipment such as corneal aberrometry. There is a need to also know the confidence with which ocular aberration measurements can be made. BACKGROUND: To assess the repeatability of lower- and higher-order aberration measurements in patients with keratoconus using the irx3 wavefront aberrometer (Imagine Eyes, Orsay, France) and evaluate correlations with corneal curvature. METHODS: The irx3 wavefront aberrometer was used to measure bilateral lower- and higher-order ocular aberrations on 33 participants with keratoconus. Three measurements were taken from each eye to determine the repeatability of lower-order aberrations (quantified as sphere and cylinder in dioptres) and higher-order aberration co-efficients (up to eighth order in micrometres), coma, trefoil and total higher-order aberration root mean square (in micrometres). Corneal curvature was measured using the Pentacam HR system (OCULUS, Wetzlar, Germany). RESULTS: Repeat measurements for lower-order aberrations resulted in larger co-efficients of repeatability than higher-order aberrations. Similarly, larger co-efficients of repeatability between repeated measures across all Zernike co-efficients were observed in eyes with severe keratoconus (that is, corneal curvature > 52-D) compared to eyes with flatter corneas. The difference between repeated measures tended to be significant for the lower-order aberrations regardless of corneal curvature. The highest correlations with corneal curvature for right and left eyes respectively, were identified for total higher-order aberration root mean square (r = 0.92, p < 0.001 and r = 0.91, p < 0.001), followed closely by coma (r = -0.93, p < 0.001 and r = -0.86, p < 0.001) and the Z (3, -1) co-efficient (r = -0.92, p < 0.001 and r = -0.86, p < 0.001 for right and left eyes, respectively). CONCLUSIONS: Lower-order aberrations tended to be less repeatable, indicating that instrument variability must be considered when monitoring progression. Total higher-order aberration root mean square and third-order aberrations, in particular the vertical coma Z (3, -1) co-efficient, demonstrated a stronger correlation with corneal curvature than the lower-order aberrations.

Effects of Monocular Atropinization on Refractive Error and Eye Growth in Infant New World Monkeys.

Purpose: To explore the effect of topical atropine on axial eye growth and emmetropization in infant marmosets. Methods: Atropine was applied to one eye from the age of 7 to 56 days in two dose regimens, High (0.1-1% twice daily, increasing with age) or moderate (Mod) (0.1% once daily). Both eyes of the marmosets were refracted, and axial dimensions were measured ultrasonically, at 14, 28, 42, 49, 56, 70, 105, 168, and 279 days of age. The time course of each measured variable was analyzed using multilevel mixed-effects modeling realized in R. Results: The logistic growth curves fitted to anterior segment depth (ASD) did not differ significantly between the dose regimens, but xmid, the age at which growth was half-maximal, and scal, the time constant of the exponential term in the logistic growth curve equation, differed significantly between the ASD of atropinized and untreated eyes (P = 0.03 and P < 0.0001, respectively), with the ASD of atropinized eyes shorter than that of untreated eyes. The splines fitted to lens thickness did not vary significantly with dose, but differed significantly (P < 0.0001) between the atropinized and untreated eyes, with the atropinized lenses thicker. Vitreous chamber depth (VCD) was not significantly different, but the variance of VCD was significantly greater (P < 0.001) in the atropinized compared with the untreated eyes. Refractive error (RE) became relatively myopic in atropinized eyes. The variance of RE in atropinized eyes was significantly greater (P < 0.0001) than in untreated eyes. Conclusions: Atropine caused the infant marmoset lens to move forward and thicken, a relative myopia, and increases in the between-animals variance in VCD, which could be considered a failure of emmetropization.

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

BACKGROUND: 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. METHODS: Over 10,000 records from patients referred for optic nerve head assessment were reviewed and 31 patients with a final diagnosis of likely neuropathic lesions posterior to the eye were included in the current study. Fundus photographs, optic coherence tomography images and visual field tests were evaluated for changes with respect to retinal nerve fibre layer topography and prediction of structure-function paradigms. Emerging clinical patterns were examined for their consistency with the likely anatomical origin of the underlying insult in the presence of varying diagnoses. RESULTS: Data from patients with lesions along the visual system allowed identification of retinal nerve fibre layer asymmetry correlated with visual field defects and ganglion cell analysis. Bilateral discordance in retinal nerve fibre loss easily discernible from an altered pattern of the temporal-superior-nasal-inferior-temporal curve was characteristic for post-chiasmal lesions. These sometimes-subtle changes supported diagnosis in cases with multiple aetiologies or with ambiguous visual field analysis and/or ganglion cell loss. CONCLUSION: Intricate knowledge of the retinal architecture and projections allows coherent predictions of functional and structural deficits following various lesions affecting the visual pathway. The integration of adjunct imaging and retinal nerve fibre layer thinning will assist clinicians to guide clinical investigations toward a likely diagnosis in the light of significant individual variations. The case series presented in this study aids in differential diagnosis of retrograde optic neuropathies by using retinal nerve fibre layer asymmetric patterns as an important clinical marker.

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.

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.

BACKGROUND: Subjects 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. FINDINGS: Two patients with Stargardt's 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. CONCLUSIONS: Spatial resolution at the eccentric locus appears as a determinant factor to select the retinal area for reading. Reading strategies in patients with Stargardt's disease and a ring scotoma demonstrate a pattern of coordination of both eccentric and central retinal loci, reflecting a high degree of adaptation.

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.

ERGs in children with pancreatic enzyme insufficient and pancreatic enzyme sufficient cystic fibrosis.

OBJECTIVES: We recorded scotopic and photopic flash electroretinograms (ERGs) in pediatric subjects with cystic fibrosis, aged 4 to 18 years, who were either pancreatic insufficient (PI) or pancreatic sufficient (PS). The aim of the study was to determine whether vitamin supplementation in the PI group allowed comparable retinal function in these two groups. METHODS: ERGs were recorded from a mixed-gender group of 41 children and adolescents (4 to 17 years of age) with cystic fibrosis. The subjects were grouped according to pancreatic function into PI (n = 29) and PS (n = 12). Full-field flash ERGs were recorded from one eye using a DTL fiber. The pupil was dilated prior to recording using two drops of 0.5% tropicamide. ISCEV photopic and scotopic stimuli and recording conditions were used. Serum levels of vitamin A, beta carotene and retinol binding protein (RBP) were measured on the day of ERG recording. RESULTS: There was no significant difference in ERG amplitudes or implicit times between PI and PS groups. Vitamin A, beta carotene, and RBP levels were not significantly different across the two groups and were not correlated with implicit times or amplitudes of any of the ERG types recorded here. CONCLUSION: Similarity of ERGs across the PI and PS cystic fibrosis patient populations tested here suggests that the supplementation protocol applied to these populations allows similar levels of retinal function (as indicated by flash ERG parameters) in the two groups.

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 (B(12)), 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.

Rotated prism-wear disrupts emmetropization but does not reliably induce hyperopia in the New World monkey.

To determine whether a disruption of binocular vision that has been previously shown to be amblyogenic disturbs visually guided growth, and in particular to follow-up the observation by Kiorpes and Wallman [Kiorpes, L., & Wallman, J. (1995). Does experimentally-induced amblyopia cause hyperopia in monkeys? Vision Research, 35(9), 1289-1297] that monkeys in whom strabismus had been induced some years earlier were hyperopic in eyes that had become amblyopic, we induced unilateral fixation in five infant New World monkeys (marmosets) through the wearing of a Fresnel prism (of 15 or 30 prism dioptres power) in front of one eye for four weeks. The prism was rotated every three hours during the prism-wear period to encourage a preference for fixating with the contralateral eye. Refractive error and intraocular axial dimensions were measured before, and at intervals after the prism-wearing period. Fixation preference was measured behaviourally, during and after the prism-wear period. Cortical visual function was subsequently assessed through recording of pattern-reversal VEPs in each marmoset between 11 and 14 months of age to assess whether amblyopia had developed in the non-fixing eye. All marmosets used the untreated eye almost exclusively for a monocular visual task by the end of the prism-rearing period. This preference was still present up to at least 7 months after prism-wear had ceased. VEP measures showed a loss of sensitivity at low spatial frequencies (the only ones we were able to test), compatible with amblyopia having developed in the non-fixating eyes of the prism-reared marmosets. Eyes that wore prisms were not significantly different from their fellow eyes in mean refractive error or mean vitreous chamber depth (repeated measures ANOVA; P>0.05) before or at any time after prism-wear had ceased. Two marmosets developed 2-3D of anisometropia (one hyperopic and one myopic) at the end of prism-wear, that was attributable to interocular differences in vitreous chamber depth, and which decreased towards isometropia in the period following prism-wear removal. Disruption of binocular vision with rotating prisms can influence emmetropization and ocular growth, although it does not appear to do so in a consistent way.

A technique to train new oculomotor behavior in patients with central macular scotomas during reading related tasks using scanning laser ophthalmoscopy: immediate functional benefits and gains retention.

BACKGROUND: Reading with a central scotoma involves the use of preferred retinal loci (PRLs) that enable both letter resolution and global viewing of word. Spontaneously developed PRLs however often privilege spatial resolution and, as a result, visual span is commonly limited by the position of the scotoma. In this study we designed and performed the pilot trial of a training procedure aimed at modifying oculomotor behavior in subjects with central field loss. We use an additional fixation point which, when combined with the initial PRL, allows the fulfillment of both letter resolution and global viewing of words. METHODS: The training procedure comprises ten training sessions conducted with the scanning laser ophthalmoscope (SLO). Subjects have to read single letters and isolated words varying in length, by combining the use of their initial PRL with the one of an examiner's selected trained retinal locus (TRL). We enrolled five subjects to test for the feasibility of the training technique. They showed stable maculopathy and persisting major reading difficulties despite previous orthoptic rehabilitation. We evaluated ETDRS visual acuity, threshold character size for single letters and isolated words, accuracy for paragraphed text reading and reading strategies before, immediately after SLO training, and three months later. RESULTS: Training the use of multiple PRLs in patients with central field loss is feasible and contributes to adapt oculomotor strategies during reading related tasks. Immediately after SLO training subjects used in combination with their initial PRL the examiner's selected TRL and other newly self-selected PRLs. Training gains were also reflected in ETDRS acuity, threshold character size for words of different lengths and in paragraphed text reading. Interestingly, subjects benefited variously from the training procedure and gains were retained differently as a function of word length. CONCLUSION: We designed a new procedure for training patients with central field loss using scanning laser ophthalmoscopy. Our initial results on the acquisition of newly self-selected PRLs and the development of new oculomotor behaviors suggest that the procedure aiming primarily at developing an examiner's selected TRL might have initiated a more global functional adaptation process.

Computer-based measurement of letter and word acuity.

Determining causes of poor reading ability is an important step in trying to ameliorate reading performance in low-vision patients. One important parameter is word acuity. The principal aim of the current study is to develop a method to reliably measure acuities for isolated lowercase letters and words of differing length that can be used to test low-vision patients. Using isolated stimuli means that testing is relatively free of potential crowding and/or distracting attentional effects from surrounding words, it is unambiguous which stimulus subjects are trying to read and response times can be recorded for each stimulus. Across a series of experiments, subjects with normal vision were asked to read isolated lowercase single letters and lowercase words of 4, 7 and 10 letters, in separate tests. Acuities for uppercase Sloan letters were also measured to provide a reference, as they are commonly used to measure visual acuity. Each test was based upon the design principles and scoring procedures used in the Bailey-Lovie and ETDRS charts. Acuities for uppercase Sloan letters were found to be equivalent whether measured using ETDRS charts or the computer-based method. Measurement of acuities for lowercase single letters and lowercase words of 4, 7 and 10 letters had a reliability that was no worse than acuities for uppercase Sloan letters. Lowercase word acuities were essentially independent of word length. Acuities for single lowercase letters and lowercase words were slightly better than uppercase Sloan letters acuity. Optimal processing of lowercase single letters and 4-, 7- and 10-letter words occurred at character sizes that were at least 0.2-0.40 log MAR above acuity threshold, i.e. between 1.5 and 3 times threshold acuity for that particular stimulus. In general, critical character sizes appear similar across word lengths as progressive increases or decreases in these values were not observed as a function of the number of letters in the stimulus. We conclude that a computer-based method of stimulus presentation can be used to obtain highly repeatable measures of acuity for lowercase single letters and lowercase words in normal vision.

The relationship between word length and threshold character size in patients with central scotoma and eccentric fixation.

BACKGROUND: Understanding limitations on text reading with eccentric fixation is of major concern in low vision research. Our objective was to determine, in patients with a central scotoma, whether threshold character size is similar for different word lengths and paragraphed texts. METHODS: In 19 patients, we retrospectively analyzed the relationship between minimum readable character size for isolated words and text. Isolated letters, two, five, and ten-letter words and a paragraphed text were presented randomly through a scanning laser ophthalmoscope in eight different character sizes. RESULTS: Threshold character size varied according to the text stimulus (p<0.05). Threshold character sizes for single letters and two-letter words were matched (p>0.99), as were those for five-letter words, ten-letter words, and paragraphed text (p>0.99). Threshold character size for single letters and two-letter words was significantly lower than that measured with other text stimuli. DISCUSSION: Reading performance is influenced by a variety of factors such as crowding, contextual effects, visual span, degree of oculomotor adaptation needed, and frequency of a defined word. Globally, when reading with a central scotoma, it appears that within word characteristics have more impact than inter-word parameters on threshold character size.

Primary viscocanalostomy for juvenile open-angle glaucoma.

PURPOSE: To evaluate the efficacy and safety of primary viscocanalostomy for medically uncontrolled juvenile open-angle glaucoma (JOAG). DESIGN: Prospective, noncomparative, interventional case-series study. METHODS: The study included 20 eyes of 20 consecutive patients with medically uncontrolled JOAG who were treated by viscocanalostomy at one institution. No surgical or laser procedure preceded viscocanalostomy. Surgical outcome was defined as an overall success by the following criteria: no visual field deterioration, no optic-neuropathy progression, postoperative intraocular pressure IOP < or =20 mm Hg, and IOP reduction > or =30% compared with baseline values with or without medication. When medications were not required, success was defined as complete. Cases that did not fulfill the aforementioned criteria and cases in which a surgical revision or further goniopuncture was performed were defined as a failure. RESULTS: Gender distribution was similar. Fourteen eyes belonged to the white race; five eyes belonged to the black race, and one eye belonged to Arab ethnicity. Mean age (+/-SD) at operation was 33.77 +/- 6.16 years, with the mean preoperative IOP (+/-SD) at 22.9 +/- 4.77 mm Hg. Thirty-six months after operation, 16 cases (80%) were considered an overall success. In 11 cases (55%), success was complete. Four cases (20%) were considered failures. No serious complications were documented either during or after operation. In two cases (10%), we documented a spontaneously reabsorbed microhyphema. Trabeculo-Descemet-membrane microperforation occurred in two cases (10%). In two other cases (10%), Trabeculo-Descemet-membrane perforation occurred and was accompanied by iris prolapse that needed peripheral iridectomy. CONCLUSION: Primary viscocanalostomy can efficiently and safely reduce intraocular pressure in cases of medically uncontrolled JOAG and provide a rational alternative to conventional surgical modalities.

Development of a viewing strategy during adaptation to an artificial central scotoma.

Although many individuals with a central scotoma develop eccentric fixation most often beneath or left of the scotoma, little is known about how they come to develop a particular viewing strategy. We investigated this by asking eight subjects with normal vision to read isolated letters, words and text passages while an artificial scotoma covered a central portion of the visual field. We quantified viewing strategy and analysed changes in their viewing behaviour over 8-10 sessions within a two-week period. Subjects read while either a horizontal (n=4) or vertical bar scotoma (n=4), 10 degrees wide, covered the entire horizontal or vertical meridian of the stimulus field. For the horizontal scotoma group: (1) there was an increasing preference to use the inferior visual field for isolated letters/words and text passages, which was essentially complete within the test period; (2) the superior visual field was preferred when reading letters/words initially presented in upper visual space and the inferior visual field when reading letters/words initially presented in lower visual space; (3) in general, variation in viewing strategy according to stimulus position diminished over the sessions for all stimuli. For the vertical scotoma group: (1) two subjects used the left and right visual fields in approximately equal proportion to view isolated letters/words, one subject showed a weak preference to use the left visual field and one subject developed a strong preference for using the right visual field; (2) the text passages could be read with combined use of left and right visual fields in a specific manner; (3) the left visual field was preferred to view stimuli initially presented in left visual space while the right visual field was preferred for words initially presented in right visual space. This effect diminished across sessions. Overall, these findings indicate that (1) a specific viewing strategy can be developed through as little as 5 hours of reading experience without guided training; (2) two distinctly separate retinal areas can be used in an integrated manner during reading; (4) stimulus position in visual space can influence viewing strategy; (5) in general, reading encourages a preference for the inferior over the superior visual field, but not the left over right visual field. Letter/word/text recognition and reading speeds increased progressively across sessions, even after scotoma lateralisation appeared stabilised suggesting that multiple mechanism are involved in adaptive changes.

Pars-plana vitrectomy alone vs vitrectomy with scleral buckling for primary rhegmatogenous pseudophakic retinal detachment.

PURPOSE: To compare primary pars-plana vitrectomy (PPV) alone vs vitrectomy with an encircling scleral buckling procedure for the treatment of primary rhegmatogenous pseudophakic retinal detachment (PsRD). DESIGN: Prospective, nonrandomized, comparative study. METHODS: All 71 eyes of 68 consecutive patients with PsRD presented to our service between 1998 and 2002 were offered either vitrectomy alone (group-A) or vitrectomy in combination with encircling scleral buckling procedure (group-B). Preoperative and postoperative patient characteristics were recorded in detail. Main outcome measures were reattachment with a single surgery, visual acuity, and reattachment surgery-related complications. RESULTS: Retina reattachment with a single surgery was achieved in 97.78% in group A and 92.31% in group B. Visual acuity improved by 3 or more lines in 60% in group A and 69% in group B. Mean postoperative refractive error change (spherical) was -0.05 diopters in group A and -1.43 diopters in group B. Postoperative intraocular pressure on long-term follow-up was elevated in 4.44% (group A) and 34.61% (group B). Average follow-up was 12.45 months (+/-5.23 SD) ranging from 9 to 40 months. We detected additional breaks intraoperatively in 54.9% of cases (both groups). CONCLUSIONS: Vitrectomy is an effective initial treatment for PsRD, whereas the benefit of an additional encircling buckling procedure is questionable.

Visual consciousness in health and disease.

Conscious experience is an essential part of normal human life and interaction with the environment. Yet the nature of consciousness and conscious perception remains a mystery. Because of its subjective nature, consciousness has been difficult to investigate scientifically, but clues have been gained through studies involving patients with cortical lesions. During the past decade, the development of event-related fMRI has provided insights into aspects of conscious perception in control subjects and patients with cortical lesions by correlating awareness and performance with neural activity during visual tasks. This article reviews how recent research has advanced understanding of conscious perception, its relationship to neural activity and visual performance, and how this relationship can be altered by visual dysfunction. It also presents recent research about how conscious awareness of vision might be represented at a neural level in the central nervous system.