Assessing professional competence in optometry - a review of the development and validity of the written component of the competency in optometry examination (COE).

BACKGROUND: Credentialing assessment for overseas-educated optometrists seeking registration in Australia and New Zealand is administered by the Optometry Council of Australia and New Zealand. The aim was to review the validation and outcomes of the written components of this exam to demonstrate credentialing meets entry-level competency standards. METHODS: The Competency in Optometry Examination consists of two written and two clinical parts. Part 1 of the written exam comprises multiple choice questions (MCQ) covering basic and clinical science, while Part 2 has 18 short answer questions (SAQ) examining diagnosis and management. Candidates must pass both written components to progress to the clinical exam. Validity was evaluated using Kane's framework for scoring (marking criteria, item analysis), generalization (blueprint), extrapolation (standard setting), and implications (outcome, including pass rates). A competency-based blueprint, the Optometry Australia Entry-level Competency Standards for Optometry 2014, guided question selection with the number of items weighted towards key competencies. A standard setting exercise, last conducted in 2017, was used to determine the minimum standard for both written exams. Item response theory (Rasch) was used to analyse exams, produce reliability metrics, apply consistent standards to the results, calibrate difficulty across exams, and score candidates. RESULTS: Data is reported on 12 administrations of the written examination since 2014. Of the 193 candidates who sat the exam over the study period, 133 (68.9%) passed and moved on to the practical component. Ninety-one (47.2%) passed both the MCQ and SAQ exams on their first attempt. The MCQ exam has displayed consistently high reliability (reliability index range 0.71 to 0.93, average 0.88) across all 12 administrations. Prior to September 2017 the SAQ had a set cutscore of 50%, and the difficulty of the exam was variable. Since the introduction of Rasch analysis to calibrate difficulty across exams, the reliability and power of the SAQ exam has been consistently high (separation index range 0.82 to 0.93, average 0.86). CONCLUSIONS: The findings from collective evidence support the validity of the written components (MCQ and SAQ) of the credentialing of the competency of overseas-educated optometrists in Australia and New Zealand.

GABAB1 and GABAB2 receptor subunits co-expressed in cultured human RPE cells regulate intracellular Ca2+ via Gi/o-protein and phospholipase C pathways.

GABAB receptors associate with Gi/o-proteins that regulate voltage-gated Ca(2+) channels and thus the intracellular Ca(2+) concentration ([Ca(2+)]i), there is also reported cross-regulation of phospholipase C. These associations have been studied extensively in the brain and also shown to occur in non-neural cells (e.g. human airway smooth muscle). More recently GABAB receptors have been observed in chick retinal pigment epithelium (RPE). The aims were to investigate whether the GABAB receptor subunits, GABAB1 and GABAB2, are co-expressed in cultured human RPE cells, and then determine if the GABAB receptor similarly regulates the [Ca(2+)]i of RPE cells and if phospholipase C is involved. Human RPE cells were cultured from five donor eye cups. Evidence for GABAB1 and GABAB2 mRNAs and proteins in the RPE cell cultures was investigated using real time polymerase chain reaction, western blots and immunofluorescence. The effects of the GABAB receptor agonist baclofen, antagonist CGP46381, a Gi/o-protein inhibitor pertussis toxin, and the phospholipase C inhibitor U73122 on [Ca(2+)]i in cultured human RPE were demonstrated using Fluo-3. Both GABAB1 and GABAB2 mRNA and protein were identified in cell cultures of human RPE; antibody staining was co-localized to the cell membrane and cytoplasm. One-hundred micromolars of baclofen caused a transient increase in the [Ca(2+)]i of RPE cells regardless of whether Ca(2+) was added to the buffer. Baclofen-induced increases in the [Ca(2+)]i were attenuated by pre-treatment with CGP46381, pertussis toxin, and U73122. GABAB1 and GABAB2 are co-expressed in cell cultures of human RPE. GABAB receptors in RPE regulate the [Ca(2+)]i via a Gi/o-protein and phospholipase C pathway.

Emmetropization in chicks uses optical vergence and relative distance cues to decode defocus.

When visual information is confined to one object plane, the emmetropization end-point is adjusted in accord with the corresponding incident optical vergence at the eye [Proceedings of the 7th International Conference on Myopia (2000) 113]. We now report the effect of adding extra visual information beyond the target plane. Visual conditions were controlled using a cone-lens system: black Maltese cross targets on white opaque backgrounds (OMX) were attached to the open faces of 2.5 cm translucent cones fitted with either 0, +25 or +40 D imaging lenses. An alternative target (TMX) was made by substituting the opaque target background for a transparent background, which allowed access to visual information beyond the target plane. The imaging devices were applied to 7-day-old chicks and worn for 4 days. Prior to this treatment, on day 2, some chicks underwent ciliary nerve section (CNS) to preclude accommodation. All treatments were monocular. Refractive errors and axial ocular dimensions were measured using retinoscopy and A-scan ultrasonography under halothane anesthesia. Treatment effects were specified as mean ( +/-S.D.) interocular differences. Eyes with the OMX/+40 D lens combination remained emmetropic (+0.73 +/-3.57 D), consistent with the target plane being approximately conjugate with the retina. Switching to the TMX caused a hyperopic shift in refractive error (+3.78 +/-3.41 D). This relative shift towards hyperopia in switching from the OMX to the TMX target also occurred for the other two lens powers. Thus, the OMX/+25 D lens induced myopia (-7.00 +/-5.88 D), corresponding to the imposed hyperopic defocus (target plane now imaged behind the retina), and switching to the TMX resulted in a reduction in myopia (-1.73 +/-5.36 D). The OMX/0 D lens combination produced the largest myopic shift, and here, switching to the TMX condition almost eliminated the myopic response (-15.50 +/-6.62 D cf. -0.56 +/-1.24 D). This relative hyperopic shift associated with switching from the OMX to the TMX target was eliminated by CNS surgery. Thus, the two CNS/TMX groups were both more myopic than the equivalent no CNS/TMX groups (+40 D lens: -2.66 +/-2.34 D; +25 D lens: -7.97 +/-6.87 D). When the visual information is restricted to one plane, incident optical vergence appears to direct emmetropization. Adding visual information at other distances produces a shift in the end-point of emmetropization in the direction of the added information. That these effects are dependent on the integrity of the accommodation system implies that accommodation plays a role in emmetropization and represents the first reported evidence of this kind.

The effect of under and over refractive correction on visual performance and spectacle lens acceptance.

As a follow-on from a previous study by Miller, Kris and Griffiths (1997, Optom. Vis. Sci. 84, 521-526), we investigated the effect of small prescription errors on spatial visual performance and spectacle lens acceptability. We included both negative and positive errors and binocular and monocular errors. Data were collected on 15 young adult subjects. Clinical measures were taken of pupil size, ocular dominance, binocular visual acuity, negative and positive relative accommodation, distance and near heterophorias, and stereopsis. Visual performance was measured with the best correction and for +/-0.50 D spherical binocular and monocular errors. Subjects wore spectacles, each containing a different error in turn, for 2 days and compared them with a reference pair. Following the wearing period subjects assessed the performance of the spectacles by completing a short questionnaire. The only ocular tests for which these small prescription errors had significant effects were binocular visual acuity and negative relative accommodation. No significant relationship was observed between any of the clinical test results and overall lens acceptance. Despite this, the reference pair was generally perceived as better than the test pairs containing errors, and a considerable proportion of subjects reported pairs with errors as being unacceptable. In conclusion, the questionnaire findings support the need for both accurate monocular and binocular refractions. Subjects differed in their criteria for judging lens acceptability.

Optical correction of form deprivation myopia inhibits refractive recovery in chick eyes with intact or sectioned optic nerves.

The finding that the eyes of young chicks recover quickly from form deprivation myopia (FDM) has been interpreted as indirect evidence for active emmetropization. More direct evidence would be the demonstration that correction of FDM with spectacle lenses, thereby removing the defocus signal, prevents recovery. We investigated this issue in eyes with intact and sectioned (ONS) optic nerves. Previous studies suggest that an intact optic nerve is necessary for accurate emmetropization. Seventy day-old male chicks were monocularly deprived using velcro-mounted diffusers, which were removed after 5-6 days and in some (n=51), but not all cases, replaced by spectacle lenses (-5, -10 or -15 D). Approximately half (n=34) of the chicks also underwent ONS on day 1. Refractive errors and axial ocular dimensions were measured when the diffusers were first removed and thereafter at 2-4 day intervals over the following 1-2 weeks. In one case, measurements were continued at less regular intervals to 33 days. Lens powers were selected to either approximately correct or under-correct the refractive errors present when the diffusers were removed. Form deprivation in normal chicks produced large myopic shifts in refraction (means for groups range from -9.20 to -16.07 D). When the deprivation treatment was terminated, the myopia quickly decreased to negligible levels unless optically corrected. Correcting lenses stabilized the myopia to a level consistent with the lens power used. Interocular differences in axial length were consistent with an axial origin to the refractive changes. Results for the ONS groups exhibited similar trends although there was increased variability in the data. The findings support the interpretation that recovery from FDM is a product of active emmetropization. That ONS increased the variability of such responses implies that an intact optic nerve is required for accurate emmetropization.

Timolol lowers intraocular pressure but does not inhibit the development of experimental myopia in chick.

Reports of intraocular pressure (IOP) being higher in myopes than emmetropes and of myopes being over-represented in glaucoma statistics, are consistent with a role of IOP in the excessive eye growth typically associated with myopia. We tested the hypothesis, based on these observations, that ocular hypotensive drugs would slow myopia progression using the chick as an animal model and timolol as an example of such a drug. To induce myopia, chicks (n = 56) were fitted with either monocular translucent diffusers or -15 D spectacle lenses from day 8. The drug treatment protocol comprised topical applications of 0.4% benoxinate, a local anaesthetic (to improve drug absorption), followed either by 0.5% timolol or distilled water (control), either daily (1000 hr) or twice daily (1000, 1600 hr). Refractive errors and ocular dimensions were measured on days 12 and 17. We also verified the ocular hypotensive effect of timolol in both normal (n = 8) and myopic (n = 12 diffusers; n = 12-15 D lenses) chicks. Here, we took baseline IOP measurements, instilled timolol and then monitored IOP over a further 5-9 hr. We found no difference in the amount of myopia produced in the timolol and control groups at either measurement time point (e.g. day 17, once per day application, diffusers: -26.9 +/- 3.3 D vs -22.7 +/- 9.1 D; lenses: -14.9 +/- 3.8 D vs -14.9 +/- 3.6 D). This was in spite of the fact that timolol did lower IOP in both normal and myopic chicks (27 and 18% reduction, respectively) While timolol does have an ocular hypotensive effect in the chick, it does not inhibit the development of myopia in this animal model.

Imposed retinal image size changes--do they provide a cue to the sign of lens-induced defocus in chick?

BACKGROUND: Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia (using negative and positive spectacle lenses); the rate of eye elongation increases in the former and slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus, although the identity of the cue(s) involved is unknown. As the spectacle lenses used in these studies generally introduce significant retinal image size differences that are in opposite directions for negative and positive lenses (minification vs. magnification), we asked whether retinal image size might provide the required sign information. METHODS: This question was addressed by manipulating retinal image size while keeping lens power constant. We also investigated the effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions. Three negative "size" lenses of approximately -11 D optical power were used, with 2 of the lenses producing magnification rather than minification as typical of negative lenses (i.e. +1.9% and +6.9% compared to -2.9%). The lenses were fitted monocularly to 7-day-old chicks, which were subsequently measured at 9 and 11 days of age (refractive error and axial dimensions). The same lens-wearing schedule was applied to two other groups of chicks that had monocular ciliary nerve section surgery to prevent accommodation 2 days posthatching; one of these groups was reared under monochromatic yellow light instead of white light. RESULTS: Near-perfect refractive compensation was seen by the end of the treatment period with all three lenses, for all three treatment groups, and there was also little difference in the rate of compensation among the various groups. In all cases, the typical responses of axial (mainly vitreous chamber) elongation and myopia were observed. CONCLUSIONS: That manipulations to retinal image size, which either decrease or reverse the usual effects of negative lenses, did not disrupt compensation to the imposed hyperopic defocus, even in the absence of accommodation and chromatic aberration cues, argues against imposed retinal image size changes being the directional cue to defocus in experimental emmetropization.

Differences in the accommodation stimulus response curves of adult myopes and emmetropes.

While the accommodation system has been implicated in myopia development, the nature of this relationship remains obscure. This study investigated the differences in accommodation stimulus response curves between adult myopes and emmetropes. Myopic subjects were classified according to age of onset and stability of their myopia. Accommodation stimulus response curves were measured using three different methods: (i) real targets presented at viewing distances of 4 m to 0.25 m, (ii) a target at 4 m viewed through negative lenses of increasing power, and (iii) a target at 0.25 m viewed through positive lenses of decreasing power. A Canon Autoref R-1 measured the accommodation responses at 5 levels of demand (increasing from 0 D to 4 D in 1 D steps). We found significant differences between the three methods used to stimulate an accommodation response in all subject groups, for example, accommodation lags at high accommodative demands were greatest for the negative lens series and least for the positive lens series. In addition, while differences between early-onset myopes, late-onset myopes and emmetropes were not observed, we did observe differences when myopic subjects were reclassified according to whether their myopia was progressing or stable. A reduced accommodation response to negative lens-induced accommodative demand was found in progressing myopes but not in stable myopes. These results provide further evidence for the link between myopia progression and inaccurate accommodation. The data also suggest that adult myopes with stable refractive errors show accommodation responses similar to that of emmetropes.

Hyperopia is predominantly axial in nature.

PURPOSE: Myopia has been found to be predominantly axial in nature, i.e. myopic eyes have longer than normal axial lengths, with corneal radius variations having only a small influence on the magnitude of the refractive error. In this study we assess whether a similar relationship exists for hyperopia. METHODS: Biometric data were collected on 57 subjects with either emmetropic or hyperopic refractive errors ranging in magnitude from -0.37 D to +17.25 D. Our main analysis concentrated on subjects with less than +10 D of hyperopia (group 1, n = 53), as subjects with +10 D of hyperopia or more (group 2, n = 4) exhibited marked differences in their biometric characteristics. RESULTS: Analysis of group 1 data revealed a significant relationship (r2 = 0.611, p = 0.0001) between the degree of hyperopia and the measured axial lengths. A weak but statistically significant relationship (r2 = 0.128, p = 0.009) was also found between mean corneal radius measures and mean spherical refractive errors, with the mean corneal radius flattening with increasing hyperopia. In group 2, three of the four subjects exhibited much steeper corneal characteristics than predicted from the group 1 data. CONCLUSIONS: Our results suggest that hyperopia, like myopia, is predominantly axial in nature, although the corneal radius also plays a role in determining refractive error magnitude. These results have implications for refractive surgery and visual performance in hyperopic eyes.

Sharp vision: a prerequisite for compensation to myopic defocus in the chick?

PURPOSE: Compensatory responses to focusing errors imposed by spectacle lenses in chicks, tree shrews and primates leave little doubt that active emmetropization can occur, and debate is now centered on whether this process is uni-directional or bi-directional in nature. To provide further insight into this emmetropization process, the studies reported in this paper addressed the question of whether access to sharp vision is necessary for compensation to myopic defocus in the chick. METHODS: Two different experimental paradigms were used to address the above question: (A) Myopic defocus was imposed, either with +15 or +40 d lenses alone or with +15 D lenses on eyes made myopic by 7 days of form deprivation; these treatments result in a shift in the plane of focus of the eye (far point) to 6.67, 2.5 cm and approximately 3.5 cm resp., with only objects at or closer than these planes being in focus. The addition to the lenses of stand-off cones, either 2.5 or 5 cm in length, further limited access to (or precluded) sharp vision by controlling how closely the chicks could approach objects. One group that had sharp vision precluded also underwent optic nerve section. (B) A range of positive lenses (+15 to +65 D) were used on their own to impose myopic defocus; for the high power lenses, access to sharp vision was very restricted because of the close proximity of the new far point (1.54 cm for +65 D lens). Refractive errors and axial ocular dimensions were measured in all experiments. RESULTS: In the first study (A), preclusion of sharp vision not only prevented compensation but resulted in increased eye growth and myopia. This myopia, like form-deprivation myopia, was unaltered by optic nerve section surgery. Limiting but not precluding sharp vision resulted in partial compensation. In the second study (B), good compensation was observed with the +15 D lens but compensation progressively declined for higher powers, with the +50 D lens having no apparent effect on eye growth and refraction and the +65 D lens inducing myopia instead of hyperopia. CONCLUSIONS: Together these results argue that some sharp vision is fundamental to compensation to impose myopia. The significance of this new finding in relation to the processes underlying active emmetropization is discussed.

Assessment of visual acuity and contrast sensitivity in the chick using an optokinetic nystagmus paradigm.

While the chick is one of the widely used animal models for eye growth studies very little is known about its visual spatial resolution performance. Using optokinetic nystagmus responses as an indicator of stimulus visibility, we estimated the visual acuity of young chicks to be between 6.0 and 7.7 cycles deg-1 at 2 and 4 days of age and slightly higher, between 7.7 and 8.6 cycle deg-1, at 8 days. Contrast sensitivity measured using the same experimental paradigm was greatest at around 1.2 cycle deg-1, for which the contrast threshold lay between 4% and 11%. Sensitivity became progressively poorer for frequencies both higher and lower than this. These data suggest that the visual performance of the chick is slightly poorer than that of the pigeon which has a similar eye size and exhibits similar foraging behaviour.

Contrast and spatial-frequency requirements for emmetropization in chicks.

This study examined the contrast and spatial-frequency requirements for emmetropization in chicks. Chicks were form deprived from hatching either constantly or had this treatment interrupted with 20 min of "visual stimulation" each day. Visual stimulation comprised exposure to either a normal cage environment (i.e., normal vision) or environments that were restricted in either their spatial contrast or spatial-frequency composition. Constant form deprivation resulted in high myopia (e.g. -11.8 D after 5 days), with refractive changes being much smaller in chicks allowed 20 min of normal vision each day (e.g. -3.4D). The restricted contrast environments (contrast range: 9-78%) were generally only slightly less effective than the normal cage environment in preventing form-deprivation myopia. However, in the case of restricted spatial-frequency environments, both the intermediate (0.86 cycles deg-1) and mixed spatial-frequency environments significantly reduced the form deprivation response, while both the high (4.3 cycles deg-1) and low spatial-frequency (0.086 cycles deg-1) stimuli, as well as the composites of these, were less effective in preventing form-deprivation myopia. This spatial-frequency dependence did not vary when, instead of white light, monochromatic illumination was used to eliminate chromatic aberration, although all groups showed more myopia under this condition. It is assumed that the observed inhibitory effects on form-deprivation myopia reflect the adequacy of the visual information presented during the period of visual stimulation for emmetropization in chicks. In this context, the data imply a mid-spatial-frequency tuning in the current study and a low contrast threshold which was not reached for this emmetropization process. Finally, the data hint that chromatic aberration may have some role as a cue to defocus in emmetropization.

The sensitivity of the chick eye to refractive defocus.

The chick is commonly used as an animal model for human myopia and emmetropization. However one criticism of this model has been the very large refractive errors that are usually induced, either by visual deprivation or through the use of lenses to first impose focussing errors. This study sought to determine the threshold for compensatory responses to imposed defocus. We observed compensation in chick eyes fitted at hatching with +1D and -1D lenses (one over each eye). Consistent with the 2D interocular difference in refraction imposed, an average of 2.13D (SD 1.0D) of anisometropia and a 0.09 mm (SD 0.05 mm) interocular difference in vitreous chamber depth were recorded after five days of lens wear. The 1 D focusing errors imposed on individual eyes are not much greater in magnitude than the estimated depth of focus of the chick eye. The significance of these results for emmetropization are discussed.

Hard contact lenses alter accommodative gain but do not prevent refractive adaptation in chicks.

This study compared the compensatory response to hyperopic defocus imposed on chicks in two different ways: (1) with-10 D spectacle lenses, and (2) with plano hard contact lens. The hyperopia seen with the contact lenses in situ was a consequence of their flat profile relative to the chick cornea, resulting in a negative fluid lens of approximately 16 D at day 2 and 9 D by day 10. This decrease with age reflects the corneal flattening that accompanies normal eye growth. By optically neutralizing the cornea, the contact lenses also had two other important effects: (1) a reduction in refractive astigmatism to almost negligible levels, and (2) a reduction in accommodative gain. The latter effect reflects the loss of the corneal component of the chick's accommodation and was estimated to be of the order of 40 to 57%, based on measurements made using topically applied nicotine to stimulate accommodation. Thus any estimate of the imposed hyperopic defocus based on accommodative effort required to overcome such errors will be too large. Chicks wearing either lens type on a continuous basis from hatching to 10 days only partially compensated for the imposed hyperopia through an increase in vitreous chamber growth. However, the effects were smaller in the spectacle lens group (e.g., a mean myopic shift of -4.1 +/- 2.3 D compared to -6.3 +/- 2.4 D for the contact lens group at day 10), although both groups experienced similar amounts of hyperopic defocus around day 10 (effective power of -10 D spectacle lens: -9.4 D). The changes seen in the spectacle lens group thus represent poorer compensation, i.e., 44 vs. 71% of the imposed error. However, overcompensation is the predicted effect, if any, of the accommodative deficit imposed on the contact lens group, and this was not seen. That compensation, albeit incomplete, occurred with the contact lens as well as the spectacle lens, suggests that neither accommodation nor astigmatism are fundamental cues for emmetropization as modeled here.

Effects on the compensatory responses to positive and negative lenses of intermittent lens wear and ciliary nerve section in chicks.

This study examined the ocular compensation to lens-induced defocus in chick and the effect of interrupting lens wear on a daily basis. Eyes fitted with +10 D lenses at hatching compensated rapidly, with almost complete compensation after 4 days of lens wear; they had decreased vitreous chamber depth compared to normal eyes and were thus hyperopic when the lenses were removed. In contrast, adaptation to the -10 D lenses was much slower, was still incomplete after 9 days of lens wear, and in this case, eyes had increased vitreous chamber depth and were myopic without the lenses. Adaptation improved when lens wear was delayed until 7 days after hatching. The effect of interrupting lens wear by periods of normal vision varied with the sign of the lenses worn. Hyperopia was always seen in response to +10 D lenses, although the magnitude of the response decreased as the duration of lens wear was decreased. In contrast, even brief periods of normal vision, i.e., 3 hr, prevented the development of myopia in response to the -10 D lenses; this apparent sensitivity to normal vision is similar to that reported for form-deprivation myopia. Ciliary nerve section used here to eliminate accommodation did not alter these response patterns.

Focusing and accommodation in the brown kiwi (Apteryx australis).

Brown kiwis are an endangered species of nocturnal, flightless birds which are native to New Zealand. The resting focus of two specimens has previously been studied by retinoscopy in a zoo while the birds were restrained by their keeper (Sivak and Howland 1987). Those birds appeared to be hyperopic (farsighted) by 2-7 D. In this study, examination with infrared photorefraction of the focusing of two unrestrained, feeding birds showed that they could focus objects at infinity and objects in their immediate environment and that they had modest powers of accommodation. Measurements on two 6 month old kiwi chicks showed their corneal radius of curvature to be between 2.90 and 3.00 mm (117 D and 101 D in power).

Retinal topography in the koala (Phascolarctos cinereus).

Nissl-stained retinal wholemounts were used to investigate the topographical organization of the ganglion cell layer of the koala (Phascolarctos cinereus); the visual resolution limit of this animal was subsequently estimated from retinal ganglion cell density data. Two types of cells could be differentiated on the basis of their size and staining characteristics: a subpopulation of presumed ganglion cells, consisting of medium to large cells with Nissl substance in the cytoplasm and pale uniformly staining nuclei, and a further subpopulation of small, densely staining cells. The latter group were presumed to be neuroglia and displaced amacrine cells. Iso-density contour maps were prepared from total cell counts and also counts of presumed ganglion cells; in all cases, the density of cells was greatest in the inferior retina where there was an area of peak density occurring as a poorly developed, horizontal streak that extended across the inferior retina. The inferior position of the streak in the koala contrasts with reports of the superior position of streaks in other marsupials. Peak cell densities of 2370 cells/mm2 and 1480 cells/mm2 were recorded for the total cell population and the presumed ganglion cell subpopulation, respectively. The latter value is equivalent to a visual resolution of 2.4 cycles/degree, based on sampling theory and a square packing paradigm, placing the koala close in visual performance to two other marsupials, the Australian Northern native cat and the American Virginia opossum.