The integrity of psychophysical visual function in non-immunocompromised PLHIV (NIPLHIV) without retinitis on antiretroviral therapy (ART).

Purpose: The present study investigated the integrity of contrast sensitivity (CS), colour vision, and pattern evoked vision potentials (VEP) in non-immunocompromised people living with HIV (NIPLHIV) without retinitis. Methods: All participants were visually asymptomatic and no history of ocular disorders, with CD4 counts above 350 cells/mm3, low viral loads and on ART. Thirty NIPLHIV and 30 age-matched HIV negative control groups underwent F100 hue colour assessment, Pelli-Robson contrast sensitivity assessment and pattern-reversal VEP. Results: The median F100 total error scores for NIPLHIV and controls was 33 (IQR: 28;41) and 28 (IQR: 26;48.50) respectively, this was statistically different (p= 0.020). The median P100 amplitude for NIPLHIV was 5.75 µV (IQR: 4.4;8.85) and 4.05 µV (IQR: 3.2;5.8) for controls, this was statistically different (p=0.045). The mean LogCS score 1.83±0.14 and the median P100 peak latency was 105.45 msec (IQR: 102.98;108.98) for NIPLHIV. Higher CD4+ counts were significantly associated with having higher F100 total error scores (OR=0.995; p=0.018), lower P100 amplitudes (OR=1.007; p=0.010) and higher P100 latencies (OR=0.994; p=0.011). Conclusion: Contrast sensitivity function, colour vision, and VEP were uncompromised in NIPLHIV. Associations between CD4 counts with F100 total error scores and P100 latency may aid in the surveillance of vision of NIPLHIV.

The relationship between retinal structure and visual function in non-immuno-compromised people living with HIV without retinitis on antiretroviral therapy.

BACKGROUND: This study sought to establish the association between retinal morphology, visual function and linear parameters of cerebral atrophy in non-immunocompromised people living with HIV (NIPLHIV). METHODS: Sixty participants (30 NIPLHIV, 30 controls), aged 18-45 years, were sourced from an outpatient clinic in South Africa. NIPLHIV on antiretroviral therapy (ART) had elevated CD4 counts and low viral loads. Macula thickness and volume measurements were obtained using the Spectralis optical coherence tomographer. Contrast sensitivity (CS), colour vision and visual-evoked potentials (VEP) were also obtained. Linear parameters of cerebral atrophy (Sylvian fissure ratio, SFR) and bicaudate nucleus ratio (BCR) were all acquired from computed tomography (CT) scans. Associations between retinal thickness and volume and visual function were established by principal component factor analysis. RESULTS: CS scores were indirectly associated with the Inner Nuclear Layer (INL)-ETDRS thickness and volume subfields (co-efficient = -0.07; p = 0.02 and -0.11; p = 0.001), respectively. F100 total error scores (TES) were directly associated with the thicknesses of Ganglion Cell Layer-ETDRS subfields (co-efficient = 6.06; p = 0.04) but indirectly associated with INL-ETDRS subfields (co-efficient = -5.49; p = 0.04). F100-TES were indirectly associated with volumes of RNFL (Retinal Nerve Fibre Layer)-ETDRS subfields (co-efficient = -5.54; p = 0.02) and inner retina -ETDRS subfields (co-efficient = -6.70; p = 0.02). P100 latency was directly associated with RNFL-ETDRS subfield thickness (co-efficient = 2.90; p = 0.02) and volumes of outer retina subfields (co-efficient = 2.72; p = 0.04). CS scores were directly associated with SFR (co-efficient = -0.04; p = 0.01). F100-TES were directly associated with BCR (co-efficient = 0.003; p = 0.004) and SFR (co-efficient = 0.002; p = 0.02). P100 latency was indirectly associated with BCR (co-efficient = -0.001; p = 0.03). CONCLUSION: The recognition of associations may be the first step in the proposal to develop a framework for the surveillance of vision in patients with NIPLHIV. We recommend a study of the sample population to track the stability of these observations before general recommendations for clinical care.

Effect of 3-Dimensional Central Stimuli on Near Point of Convergence.

AIM: Since an interaction between binocular disparity and the vergence system takes place in order to reduce retinal disparity, it is likely that vergence control, as measured with the near point of convergence (NPC), will be better if the target used for measurement has 3-dimensional (3-D) features in its most central parts. The aim of the present study was therefore to investigate if the NPC would give a better result using a fixation target with centrally placed 3-D features when compared with a two-dimensional (2-D) target. METHODS: Twenty-three asymptomatic subjects (2 men, 21 women; average age 30.0 years ± 7.36 SD) who experienced diplopia when a fixation target was brought close to the eyes had their break point NPC measured using a modified RAF-ruler. A metal cube and a printed image of the cube were used as a 3-D and 2-D stimuli. The measurements were repeated 3 times in each subject for each test condition, for a total of 6 randomized NPC measurements. RESULTS: On average a significant difference in NPC (p = 0.0172) was found for break point NPC with a 3-D stimuli (mean: 7.27 cm ± 2.37 SD), giving the better result as compared with a 2-D stimuli (mean: 8.02 cm ± 2.82 SD). Comparing the most remote recorded NPC values of the 3 repeated measurements under each stimulus condition, a significant difference was found (p = 0.0159, t = 2.612) with 3-D stimuli giving the better result. CONCLUSION: The results of this study demonstrate the influence of binocular disparity stimuli on the vergence control as NPC was better if the target used for measurement had 3-D features in its most central parts.

Central and peripheral corneal thinning in keratoconus.

PURPOSE: Recent data regarding the mid-peripheral portion of the removed corneal button in transplant surgery indicate histopathologically that keratoconus was present also in the peripheral portion of the button. The intent of this study was therefore to investigate if peripheral changes could also be detected clinically by measuring the central and peripheral corneal thickness of KC patients. METHODS: Corneal pachymetry was measured with the Visante optical coherence tomography and Orbscan II. Of 52 subjects, 26 were KC subjects and 26 were age- and sex-matched control subjects. RESULTS: Corneal thickness, in KC patients, was significantly reduced in all areas compared with corneal thickness among controls with both the Visante optical coherence tomography and Orbscan II. CONCLUSION: The results of the present study have provided clinical evidence that KC is a disease affecting a wider area of the cornea. Although the KC cornea shows the greatest change in thickness in the ectatic region, this attenuation declines toward the periphery. The presence of peripheral thinning indicated that KC may be a "pancorneal" pathology and not limited to the ectatic portion.

Rarebit fovea test in children: reference data for children aged six to 10 years.

INTRODUCTION: The most common way to examine vision is to measure visual acuity using letter charts. The Rarebit fovea test was developed for detection of small defects of foveal function at a stage before they cause abnormal visual acuity. In a recent study, the RFT was well tolerated in a smaller group of children between seven and nine years of age; however, the number of subjects in that study was small for the determination of reference values, and therefore the aim of the present study was to establish reference values for a larger group of children aged between six and 10 years and to evaluate the learning effect after repeated tests. METHODS: Rarebit fovea test data were collected from a group of 108 subjects aged between six and 10 years as part of a screening program at a compulsory school in Stockholm, Sweden. All subjects had good visual acuity and minor refractive errors. They underwent two Rarebit fovea test examinations on one occasion. RESULTS: Rarebit fovea test results ranged from a median mean hit rate of 94.0 to 97.5 per cent for pre-school and third-year children, respectively. For the entire group of children the median mean hit rate was 96 per cent (range 57 to 100). The third-year children performed significantly better than the pre-school (p < 0.01) and first-year children (p < 0.05). A significant improvement from the first to second test run was noticed in all groups. CONCLUSION: The Rarebit fovea test proved to be well tolerated among children in a group of six to 10 year olds and more than 90 per cent of children were considered to give reliable results close to what is normal for adults. It would be interesting to further investigate the potential of the Rarebit fovea test for evaluation of foveal function in children.

The influence of unilateral uncorrected astigmatism on binocular vision and fixation disparity.

PURPOSE: It is accepted practice to use a spherical equivalent power as an alternative contact lens correction for those patients with lower amounts of astigmatism, allowing for an easier fit, but the blur caused by one diopter of uncorrected astigmatism can reduce acuity of 6/6 to that of about 6/8. This is usually deemed acceptable monocularly, often retaining a good binocular acuity. The purpose of this study is to explore how monocular astigmatic blur may also affect the patient's binocular vision function. METHODS: A trial frame was outfitted with full correction for 20 healthy subjects (mean age 25.5 years, range 19-36 years) and a baseline horizontal fixation disparity was measured at a distance of 1 m. Thereafter, fixation disparity was measured with induced monocular astigmatic blur in the right eye, creating an astigmatic error in the amounts of -0.75 and -1.25 in axis 90 and axis 45. RESULTS: It was determined that the differences among full correction and the 4 different types of astigmatic blur were not significant when analyzed as one group (P = 0.5445), nor when separated into groups according to whether the subject had naturally occurring astigmatism or not, (astigmatic group, P = 0.3801; non-astigmatic group, P = 0.5899). CONCLUSIONS: Monocular astigmatic blur in the amounts of -0.75 and -1.25 did not have a significant effect on tested subjects with regard to the amount of blur or axis orientation. This low amount of blur is likely within the range of compensation for the subjects, proving that spherical equivalent contact lenses are a viable option for low amounts of astigmatic error.

Vergence adaptation in subjects with convergence excess.

The main purpose of this study was to evaluate the vergence adaptive ability in subjects diagnosed with convergence excess (CE) phoria (ie, subjects with an esophoric shift from distance to near but without an intermittent tropia at near). Vergence adaptation was measured at far and near with both base-in and base-out prisms using a "flashed" Maddox rod technique in 20 control subjects and 16 subjects with CE. In addition, accommodative adaptation and the stimulus AC/A and CA/C cross-links were measured. The AC/A and CA/C ratios were found to be high and low, respectively, and accommodative adaptation was found to be reduced in CE subjects as compared with the controls (P<0.005), all as predicted by the present theory. However, vergence adaptive ability was found to be reduced in the CE subjects at both distance and near and in response to both base-in and base-out prisms (P=0.002). This finding is not in accordance with and is difficult to reconcile with the present theory of CE.

Fixation stability during Rarebit Fovea Test.

BACKGROUND: Unstable fixation has been reported to be a common cause of unreliable results in perimetry. The Rarebit Fovea Test (RFT) is a computerised foveal function test that evaluates the 4 x 3 degrees central visual field, using very small test stimuli. To minimise the test time, no fixation control is used. Instead, stable fixation is facilitated by the use of a dynamic fixation target. The aim of the current study was to evaluate fixation stability during a RFT examination by continuous recording of the eye movements. METHOD: Twelve healthy subjects were enrolled in the study together with two amblyopic subjects. A three-dimensional eye tracker was used to measure eye movements during two test sessions. All subjects went through one session of fixation measurement with stimulus presentation and one session without stimulus presentation. Both sessions lasted approximately 90 seconds. RESULTS: Mean hit rate (MHR) in the whole group was 89.7 per cent. Five out of 14 subjects had abnormal RFT results. There was no significant difference in fixation stability either between the test sessions with and without stimulus presentations (p = 0.79) or between the subjects with abnormal (n = 5) and normal (n = 11) MHR, (p = 0.55). CONCLUSION: Fixation seems stable during RFT testing, thus the test design and fixation target used in the RFT could be considered adequate, at least in subjects with normal or near normal visual function. Further studies are needed to evaluate how different visual abnormalities will affect fixation stability during RFT testing.

Corneal and conjunctival epithelial staining in hydrogel contact lens wearers.

OBJECTIVES: The purpose of this study was to investigate the prevalence of conjunctival and corneal epithelial staining in soft contact lens wearers and to see if staining could be associated with factors such as type of lens worn, wearing time, care system, age, and sex. METHODS: The records of 338 adapted hydrogel contact lens wearers were examined retrospectively. RESULTS: Conjunctival staining was found to be present in 32.5% of the subjects and corneal staining was found to be present in 19.5% of subjects. None of the subjects had staining above grade 2 using the Cornea and Contact Lens Research Unit scale. Because of the low prevalence of staining, the low grading of staining found and the large variation in refractive power, lens type worn, wearing modality, and solution used statistical analysis for association between staining and different factors could only be performed for the association between sex and staining and between corneal and conjunctival staining. However, no statistical significant association could be demonstrated. DISCUSSION: Despite the low prevalence of staining the conjunctiva and cornea should be examined carefully in contact lens wearers and prospective wearers because the conjunctival and corneal epithelium serve as protective barriers for the underlying layers of the cornea and conjunctiva. To allow comparison of data obtained in different studies assessing corneal staining, it is recommended that clinicians develop and adopt a universal standard protocol for this measure.

Effects of orthoptic treatment on the CA/C and AC/A ratios in convergence insufficiency.

PURPOSE: To evaluate the effect of orthoptic treatment on the AC/A (A, accommodation; C, convergence) and CA/C ratios in subjects with convergence insufficiency (CI). METHODS: The change in AC/A and CA/C ratios after a 12-week period of home-based orthoptic treatment was examined in 10 subjects (mean age, 25.4+/-4.1 years [SD]). Both the AC/A and CA/C ratios were measured by using gradient response methods. For the AC/A ratio, the gradient phoria method was used, and for the CA/C ratio the prism-induced change in accommodation was measured with a refractometer. RESULTS: No change in the AC/A and CA/C ratios (P>0.05) were found after orthoptic treatment. However, improvements were found (P<0.05) in the fast and slow vergence mechanisms. CONCLUSIONS: Despite improvements in the fast and slow vergence mechanisms no change was found in the AC/A and CA/C ratios after orthoptic treatment in CI subjects. This finding is unexpected in light of the present understanding of CI, and an alternative theory is proposed.

Measurements of objective and subjective fixation disparity with and without a central fusion stimulus.

BACKGROUND: Fixation disparity is the condition in which the images of a binocularly fixated object are not imaged on exactly corresponding retinal points, but are still within Panum's fusional areas. Measurements of objective and subjective fixation disparity have indicated that subjective fixation disparity does not indicate the true eye position. However, the effect of the foveal fusional lock (FFL) on the relationship between objective and subjective fixation disparity is still not clear. MATERIAL/METHODS: This relationship was investigated in five subjects. The objective measurements were made using scleral search coils, and at the same time the Sheedy distance disparometer indicated the subjective fixation disparity. Measurements were obtained both with and without an FFL. RESULTS: It was found that without an FFL there was a significant difference (p<0.05) between subjective and objective fixation disparity, whereas when an FFL was added, the difference was no longer significant. Additionally, the absolute sizes of both SFD and OFD were found to be significantly smaller with the FFL. CONCLUSIONS: These results indicate that the presence of an FFL makes subjective fixation disparity a more accurate indicator of the objective eye position. An instrument with an FFL should therefore be used clinically. The difference between objective and subjective fixation disparity presumably indicates a change in correspondence.