A. Jonathan Jackson

Uniformity of Visual Acuity Measures in Published Studies

PURPOSE To investigate the methods used in contemporary ophthalmic literature to designate visual acuity (VA). METHODS Papers in all 2005 editions of five ophthalmic journals were considered. Papers were included if (1) VA, vision, or visual function was mentioned in the abstract and (2) if the study involved age-related macular degeneration, cataract, or refractive surgery. If a paper was selected on the basis of its abstract, the full text of the paper was examined for information on the method of refractive correction during VA testing, type of chart used to measure VA, specifics concerning chart features, testing protocols, and data analysis and means of expressing VA in results. RESULTS One hundred twenty-eight papers were included. The most common type of charts used were described as logMAR-based. Although most (89.8%) of the studies reported on the method of refractive correction during VA testing, only 58.6% gave the chart design, and less than 12% gave any information whatsoever on chart features or measurement procedures used. CONCLUSIONS The methods used and the approach to analysis were rarely described in sufficient detail to allow others to replicate the study being reported. Sufficient detail should be given on VA measurement to enable others to duplicate the research. The authors suggest that charts adhering to Bailey-Lovie design principles always be used to measure vision in prospective studies and their use encouraged in clinical settings. The distinction between the terms logMAR, an acuity notation, and Bailey-Lovie or ETDRS as chart types should be adhered to more strictly.

Profile of Refractive Errors in Cerebral Palsy: Impact of Severity of Motor Impairment (GMFCS) and CP Subtype on Refractive Outcome

PURPOSE To describe refractive status in children and young adults with cerebral palsy (CP) and relate refractive error to standardized measures of type and severity of CP impairment and to ocular dimensions. METHODS A population-based sample of 118 participants aged 4 to 23 years with CP (mean 11.64 +/- 4.06) and an age-appropriate control group (n = 128; age, 4-16 years; mean, 9.33 +/- 3.52) were recruited. Motor impairment was described with the Gross Motor Function Classification Scale (GMFCS), and subtype was allocated with the Surveillance of Cerebral Palsy in Europe (SCPE). Measures of refractive error were obtained from all participants and ocular biometry from a subgroup with CP. RESULTS A significantly higher prevalence and magnitude of refractive error was found in the CP group compared to the control group. Axial length and spherical refractive error were strongly related. This relation did not improve with inclusion of corneal data. There was no relation between the presence or magnitude of spherical refractive errors in CP and the level of motor impairment, intellectual impairment, or the presence of communication difficulties. Higher spherical refractive errors were significantly associated with the nonspastic CP subtype. The presence and magnitude of astigmatism were greater when intellectual impairment was more severe, and astigmatic errors were explained by corneal dimensions. Conclusions. High refractive errors are common in CP, pointing to impairment of the emmetropization process. Biometric data support this CONCLUSION In contrast to other functional vision measures, spherical refractive error is unrelated to CP severity, but those with nonspastic CP tend to demonstrate the most extreme errors in refraction.

Therapeutic contact lenses and their use in themanagement of anterior segment pathology

Abstract Therapeutic contact lenses have been advocated as an important component of anterior segment ophthalmic careregimes since the late 1960s. Despite favourable reviews in the ophthalmic literature, the perception remains, among contact lens and corneal specialists alike, that the benefits associated with this type of treatment should be considered only as a last resort. The results obtained in 46 consecutive cases fitted with either hydrogel or silicone therapeutic lenses, over an 18-month period are reviewed. Results indicate that successful therapeutic lens programmes can be achieved through a combination of appropriate patient and lens selection, and the initiation of a suitable management strategy. Approximately 25% of patients were fitted successfully with a conventional hydrogel low water content therapeutic lens. Twenty-five per cent of patients required alternative hydrogel lenses of differing parameters. Thirty per cent required silicone lenses to overcome ocular surface and lid abnormalities which had rendered hydrogel lens wear inappropriate. Almost 80% of patients fitted achieved some success with therapeutic lenses. Virtually all of those fitted on the basis of ocular pain achieved relief during the course of the treatment. Results highlight the need for a management protocol for the provision of therapeutic bandage contact lenses on a regional basis.

The changing visual profile of children attending a regional specialist school for the visually impaired in Northern Ireland.

Aim:  To investigate the changing profile of children attending a special school for visually impaired children over a 30‐year period.

Investigating the relationship between foveal morphology and refractive error in a population with infantile nystagmus syndrome

PURPOSE We explored associations between refractive error and foveal hypoplasia in infantile nystagmus syndrome (INS). METHODS We recruited 50 participants with INS (albinism n = 33, nonalbinism infantile nystagmus [NAIN] n = 17) aged 4 to 48 years. Cycloplegic refractive error and logMAR acuity were obtained. Spherical equivalent (SER), most ametropic meridian (MAM) refractive error, and better eye acuity (VA) were used for analyses. High resolution spectral-domain optical coherence tomography (SD-OCT) was used to obtain foveal scans, which were graded using the Foveal Hypoplasia Grading Scale. Associations between grades of severity of foveal hypoplasia, and refractive error and VA were explored. RESULTS Participants with more severe foveal hypoplasia had significantly higher MAMs and SERs (Kruskal-Wallis H test P = 0.005 and P = 0.008, respectively). There were no statistically significant associations between foveal hypoplasia and cylindrical refractive error (Kruskal-Wallis H test P = 0.144). Analyses demonstrated significant differences between participants with albinism or NAIN in terms of SER and MAM (Mann-Whitney U test P = 0.001). There were no statistically significant differences between astigmatic errors between participants with albinism and NAIN. Controlling for the effects of albinism, results demonstrated no significant associations between SER, and MAM and foveal hypoplasia (partial correlation P > 0.05). Poorer visual acuity was associated statistically significantly with more severe foveal hypoplasia (Kruskal-Wallis H test P = 0.001) and with a diagnosis of albinism (Mann-Whitney U test P = 0.001). CONCLUSIONS Increasing severity of foveal hypoplasia is associated with poorer VA, reflecting reduced cone density in INS. Individuals with INS also demonstrate a significant association between more severe foveal hypoplasia and increasing hyperopia. However, in the absence of albinism, there is no significant relation between refractive outcome and degree of foveal hypoplasia, suggesting that foveal maldevelopment in isolation does not impair significantly the emmetropization process. It likely is that impaired emmetropization evidenced in the albinism group may be attributed to the whole eye effect of albinism.

Low-contrast acuity measurement: does it add value in the visual assessment of down syndrome and cerebral palsy populations?

PURPOSE Children with Down syndrome (DS) and cerebral palsy (CP) often have reduced visual acuity (VA). This study assessed VA and low-contrast acuity (LCA) with Lea symbols in DS and CP populations to explore whether LCA measures provide useful additional information about visual performance. VA and LCA were also measured in a large group of typically developing young people. METHODS High-contrast VA and LCA performance was measured monocularly using crowded Lea symbols with 45 young people with CP (mean age 11.8 ± 4 years), 44 with DS (mean age 10.5 ± 3 years), and 211 controls (mean age 11.4 ± 3 years). Refractive status was confirmed with cycloplegic retinoscopy. RESULTS DS AND CP GROUPS HAD SIGNIFICANTLY LOWER ACUITIES THAN CONTROLS AT ALL CONTRASTS (P 0.001). MEAN (SD) HIGH-CONTRAST VA WAS AS FOLLOWS: DS = +0.39 ± 0.2 logMAR; CP = +0.18 ± 0.2 logMAR; controls = -0.04 ± 0.1 logMAR. Mean 2.5% LCA was as follows: DS = +0.73 ± 0.2 logMAR; CP = +0.50 ± 0.2 logMAR; controls = +0.37 ± 0.1 logMAR. For controls, the mean difference between VA and 2.5% LCA was 0.40 logMAR (95% limits of agreement, ± 0.22 logMAR). While there was a positive relation between VA and 2.5% LCA scores (linear regressions, P < 0.0001), considerable variation existed, with VA explaining only 36% of the variance in LCA performance for control data. CONCLUSIONS VA and LCA performance was significantly poorer in DS and CP groups than in controls, and high-contrast VA did not reliably predict low-contrast performance. Therefore both high- and low-contrast acuity assessment are valuable to fully describe an individuals visual function, and this may be particularly relevant in DS and CP in cases in which patients are unable to articulate visual difficulties. Age-specific reference data from a large sample of typically developing young people across a broad age range are presented for clinicians using high- and low-contrast Lea symbols.

Acute rigid gas permeable contact lens intolerance

Rigid gas permeable (RGP) and polymethylmethacrylate (PMMA) lens wearers occasionally report episodes of acute intolerance which is experienced upon lens insertion. In this paper, we report two cases of such intolerance in which the probable cause was contact lens inversion. We also present the results of a study in which a custom-built calibrated strain gauge was used to measure the force in Newtons (N), required to invert RGP lenses [oxygen permeability, or Dk, values between 30 and 90 x 10(-11) (cm2/s) (mlO2/ml x mmHg)] and PMMA lenses of different spherical back vertex powers (+/-3.00 D, 9.00 D). Significantly, less force was required to invert minus powered lenses (17.5 +/- 4.8 N) than plus powered lenses (31.7 +/- 7 .4 N), irrespective of the material. PMMA lenses required more force to induce inversion than that required to invert RGP lenses. Lenses with a Dk of 90 required only two thirds of the force (20.0 +/- 5.8 N) required to cause inversion compared to PMMA lenses (32.9 +/- 11.0 N). High powered PMMA lenses were found to be more likely to fracture on inversion than any other lenses tested. The force required to return negatively powered lenses to their original shape, once inverted, was less than 25% of that initially required to induce inversion. Plus powered lenses either reverted to their original form spontaneously, or required less than 3% of the original inversion force to do so. It was concluded that practitioners should consider inversion as a possible reason for otherwise unexplained, acute RGP contact lens intolerance experienced upon lens insertion. The reason why inversion has eluded so many, as a possible cause of intolerance, is likely to be because minimal force is required to return those lenses, which do not crack or fracture, to their original shape.

Longitudinal study of spherical refractive error in infantile nystagmus syndrome

To explore the onset and progression of spherical refractive error in a population with infantile nystagmus syndrome.

Rigid gas permeable contact lenses: Out in the cold

INTRODUCTION Rigid gas permeable (RGP) contact lens wearers may experience episodes of lens fracture during handling. In this paper, we report the case of a keratoconic contact lens wearer whose lens fractured whilst being handled at sub-zero temperatures. Subsequent studies illustrate how PMMA and RGP contact lenses behave when exposed to sub-zero temperatures. METHODS Using a previously validated custom-built strain gauge we have measured the force required to invert RGP contact lenses (Fluroperm, DK30-DK151, PMMA and Aquasil; dioptric power -2.00DS) under different temperature conditions. RESULTS It was found that RGP lenses, frozen to -7 degrees C, required on average 15% less force to cause inversion than when stored at room temperature, regardless of material. It was also found that without due care, lenses of all materials fractured more easily after having been frozen, than lenses kept at room temperature. Fracture rates rose from 8% to 83% if lenses were stored wet (at -7 degrees C) as opposed to dry. CONCLUSION The authors conclude that practitioners should consider inappropriate contact lens storage and handling as a possible reason for otherwise unexplained acute RGP contact lens fracture.

Are worldwide albinism prevalence figures an accurate reflection? An incidental finding from a Northern Ireland study

Are worldwide Albinism prevalence figures an accurate reflection? An incidental finding from a Northern Ireland studyPerson et al.,1 and Witkop et al.,2 suggest global prevalence figures for albinism of 1 in 18,000, and 1 in 17,000 respectively. Person et al.’s 1 figure is widely quoted in the literature but it is unclear how it was derived. Gronskov et al.,3 investigated birth prevalence and mutation spectrum in Danish patients with autosomal recessive albinism suggesting a minimum birth prevalence of 1 in 14,000. Similarly Froggatt4 had investigated the occurrence of albinism in Northern Ireland (NI) in 1960 and reported a prevalence of 1 in 10,000. Clearly there are discrepancies in the literature in terms of the prevalence of albinism.The Northern Ireland Nystagmus and Albinism (NINA) StudyA three year study investigating the visual and refractive profile of a population of children and adults with albinism (and control group with nystagmus) took place in NI. The Northern Ireland Nystagmus and Albinism (NINA) Study employed mass triangulation techniques to ensure maximum recruitment through the two main tertiary ophthalmic centres in NI as well as from local eye charities, and qualified teachers of the visually impaired (QTVI). The number of individuals within the study age group (0-39 years) with albinism, was estimated to be 97 based on published prevalence figures specific to NI (1 in 10,000 4). However, 148 individuals with albinism were identified (aged 0-39 years). When observing incidence of albinism in NI, once again a higher than expected occurrence was demonstrated. During a 36 month period (January 2008-December 2010) seventeen children born with albinism were recruited (7 infants born in 2010, 4 in 2009 and 6 in 2008), compared with an expected incidence of 2-3 per year.DiscussionDue to the difficulty of identifying undiagnosed cases of albinism (with minimal visual dysfunction) outside the hospital eye service (HES), from a mainly Caucasian population, it is unlikely that all those in NI living with albinism or born with this condition during the study period, were identified. Nonetheless, based on the number of individuals that were identified, the authors propose that the estimated incidence rate of albinism in NI is at least 1 in 4,500, and that estimated prevalence is at least 1 in 6,600. This is greater than the prevalence suggested by Froggatt in the 1960s. These findings support the work of Sarvanathan et al.,5 who reported a prevalence of 1 in 4,000 people with albinism in Leicestershire (UK). It is the authors’ opinion that albinism is not on the increase, rather that more individuals are being correctly diagnosed with albinism due to advancement in healthcare and diagnostic techniques, as well as increased awareness.ConclusionThe increase in numbers of people with albinism living in NI has socio-economic implications for service provision, with an increased number of families entitled to Disability Living Allowance (DLA) and other benefits (Registration as Severely Sight Impaired/Sight Impaired). Additionally, a greater number of children needing spectacles, visual aids, HES appointments, educational assessments and classroom assistants must be taken into consideration when planning future services. Although the present study was not an epidemiological prevalence survey it has highlighted that there is a larger than expected occurrence of albinism in NI. The authors suspect that this is not an isolated case and in fact that worldwide figures such as 1 in 18,000 are a significant underestimation of true prevalence.