Refractive Development and Evidence-Based Prescribing PDF

REFRACTIVE DEVELOPMENT AND EVIDENCE-BASED PRESCRIBING AUTHOR Kathryn Saunders: University of Ulster, Northern Ireland PEER REVIEWER Tim Fricke: University of Melbourne, Melbourne, Australia INTRODUCTION This lecture will build on what we have learned about normal refracti...

REFRACTIVE DEVELOPMENT AND EVIDENCE-BASED PRESCRIBING AUTHOR Kathryn Saunders: University of Ulster, Northern Ireland PEER REVIEWER Tim Fricke: University of Melbourne, Melbourne, Australia INTRODUCTION This lecture will build on what we have learned about normal refractive development in infancy and early childhood and examine what happens when the normal emmetropization process does not occur and how the evidence available from research can be used to inform our decisions regarding prescribing glasses to young children. HYPEROPIA We have seen that hyperopia is relatively common during infancy and emmetropization results in a fairly rapid decrease in hyperopic errors during the first year of life. But as optometrists we know that adult strabismic and amblyopic patients are often hyperopic, so we can imagine that when this emmetropization process fails, there seems to be a link with poor visual outcome. Research studies investigating the natural history of hyperopic children have shown that those children who retain hyperopia beyond infancy or demonstrate increases in hyperopia are far more likely to develop strabismus and amblyopia. When emmetropization fails, children have an increased risk for amblyopia and strabismus:  13x more strabismus  6x more amblyopia (Atkinson & Braddick 1988; Atkinson et al 2007; Ingram et al 1986, 1991; Aurell & Norrsell 1990) Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-1  Refractive Development and Evidence-Based Prescribing HYPEROPIA & STRABISMUS/AMBLYOPIA Some of the most well known studies of infant refractive development and the impact of hyperopia are a series conducted by Atkinson and Braddick’s group in England. In one of their studies, they recruited over 3,000 infants and used cycloplegic photorefraction to assess refractive error at 6-9 months and identify hyperopic infants with more than +3.50D in any one meridian of either eye. The infants, left uncorrected, were then re- tested at 3.5 years and 5 years of age to evaluate the refractive error and other aspects STUDY BY ATKINSON of visual function including monocular visual acuity and presence of strabismus. Further AND BRADDICK (1988) studies by the same group also examined the development of visuoperceptual, cognitive, motor and attention abilities. The group’s main findings were that significant levels of hyperopia in infancy were significantly associated with the development of strabismus during childhood and a delay in acuity development – acuity at 3.5 years was significantly poorer in the group that had been hyperopic in infancy but this difference resolved by the 5 year test. The first study we will consider from Ingram’s group involved refracting infants at 12 months and leaving them uncorrected until follow-up at 3.5 years when vision, refractive error and ocular motor posture was examined. Ingram’s findings were that those infants with high levels of hyperopia at 12 months were significantly more likely to have amblyopia at 3.5 years (48%) and there was a (less predictable) tendency for more strabismus in this group. Ingram repeated the study with a younger recruiting age of six months. The infants were again left uncorrected, but monitored in terms of intermediate refractions and then their visual outcome at 3.5 years assessed. Ingram’s group showed that infants who retained high levels of hyperopia (≥ +3.50D) STUDY BY INGRAM ET from six months of age (i.e. failed to emmetropize) were significantly more likely to have AL (1991) amblyopia and strabismus at 3.5 years and those that showed the expected reduction in hyperopia (i.e. emmetropization occurred) had a better visual outcome. A further useful finding in this study was that for those infants in which emmetropization did occur, it was complete in 82% of infants by 12 months of age. This is important to note for the optometrist. It suggests that we should be wary about correcting refractive errors prior to 12 months of age, (except in the cases of extreme, pathologically high refractive errors e.g. after cataract extraction, or extreme myopia associated with retinopathy of prematurity) as the most active phase of the emmetropization process is likely to still be ongoing. We should monitor high refractive errors up until at least the second year of life in order that we allow emmetropization to occur if it is going to. We can then intervene and prescribe if it fails to take place. We will see later that by providing spectacles we may improve visual outcome when emmetropization fails. A very specific study (by Aurell and Norrsell) of the refractive progress and visual outcome of children with a family history of strabismus and who had high hyperopia (≥ +4.00D) in infancy provides further evidence for the detrimental impact of the failure of emmetropization. These infants were identified at six months of age and left uncorrected STUDY BY AURELL by spectacles. They were reviewed at four years of age. AND NORRSELL (1990) Their findings were emphatic. All those children in this group who retained high levels of hyperopia (≥ +4D in any meridian) became strabismic and those in whom emmetropization had occurred remained orthophoric. Although the numbers in this study were small, they are stark and underline the importance of both family history and the failure of emmetropization in the presentation of childhood strabismus. Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-2  Refractive Development and Evidence-Based Prescribing Whilst it is clear that hyperopia is associated with strabismus and amblyopia it is not clear why some children emmetropize and others don’t. When emmetropization fails and the risk of strabismus and amblyopia is increased, is there anything that the optometrist can do to reduce this risk, or should we just warn parents that frequent monitoring is required to identify visual deficits as soon as they appear? What about the prescription of INFERENCE glasses? If we correct the hyperopic error with spectacles, does the risk of amblyopia and strabismus decrease? Atkinson and Braddick’s group and the work of Ingram provide us with some evidence to help us answer these questions. Astigmatism and anisometropia and their retention beyond infancy also signal an increased risk for strabismus and amblyopia. ANISOMETROPIA & STRABISMUS/AMBLYOPIA Optometrists are highly aware of the link between anisometropia and amblyopia and strabismus, as we commonly see adult amblyopes and strabismic patients with anisometropia. We know that accommodation is linked between the eyes and that a pair of eyes accommodate by the same amount, even if one eye has a different focal requirement than the other. An individual with a plano eye and a hyperopic eye will always have a blurred retinal image in the hyperopic eye as the visual system will preferentially focus the plano eye - this requires less accommodative effort. Clear associations between anisometropia,strabismus and amblyopia are demonstrated in the research literature to support the clinician’s experience. Ingram (1977) found 75% of esotropes and amblyopes to be anisometropic. The study done by Abrahamsson et al (1990b) showed persistent anisometropia to be the cause of high risk of amblyopia (25%). One might naturally imagine that the blur experienced by the more hyperopic eye is the cause of amblyopia and that the anisometropia precedes amblyopia (and strabismus if present). However, the empirical data challenge this assumption. The study of Almeder et al (1990) has been cited as evidence to challenge the assumption that anisometropia precedes amblyopia. 686 subjects were monitored from birth to 10 years of age. Their prospective data reveal only two subjects (0.03%) of the STUDY BY ALMEDER, study cohort who were persistently anisometropic (both esotropic) during infancy and PECK & HOWLAND early childhood. They expect that if persistent anisometropia were to precede amblyopia, (1990) (the blur from the anisometropia resulting in amblyopia) a higher prevalence of anisometropia would be expected. The prevalence of amblyopia in the general population is estimated at about 2-3%, not 0.03%. Prospective data from Gwiazda’s laboratory show similar findings. These data may STUDY BY GWIAZDA suggest that the majority of anisometropia seen in adult amblyopes is the result, rather (1991) than the cause of amblyopia; that the subnormal vision in the amblyopic eye has impacted on the attainment and maintenance of emmetropia in the growing eye. STUDY BY LEPARD Lepard and Abrahamsson et al inspected retrospective data from hospital eye clinics and (1975) AND found that anisometropia occurred after the onset of amblyopia in many cases, as a ABRAHAMSSON ET AL strabismic eye remained hyperopic and the fixating eye appeared to emmetropize. (1992) Abrahamsson and Sjorstrand investigated the outcome at 10 years of age of infants who had been seen in a hospital clinic with anisometropia of three dioptres or more at 12 months of age. STUDY BY ABRAHAMSSON AND Their results (Table 9.1) show clearly the impact of anisometropia (when present from SJÖRSTRAND (1996) infancy) on the visual outcome, if it does not resolve. However, it is not clear whether these infants were already amblyopic at 12 months and Abrahamsson and Sjörstrand suggest that these infants may have had an undetected microtropia in early infancy that impaired coordinated emmetropization, resulting in anisometropia. Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-3  Refractive Development and Evidence-Based Prescribing Table 9.1 Impact of Anisometropia Anisometropia Results Fully reduced No amblyopia Increased All amblyopic Partially reduced All strabismus and/or amblyopic The idea that the microtropia subsequently resolves and enables normal emmetropisation to resume, or amblyopia to develop where this doesn’t happen, has been suggested, but not widely accepted. PRESCRIBING FOR CHILDREN So how do we decide when and if a child needs glasses? We know that failure to emmetropize increases the risk of strabismus and amblyopia, but if a young hyperopic child has neither of these conditions at present and no symptoms, how we do decide if, when and what to prescribe? Will spectacles have an impact on the risk for poor visual outcome? Figure 9.1 A child with a trial frame on her face before subjective refraction Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-4  Refractive Development and Evidence-Based Prescribing When prescribing glasses to older children and adults, our decisions are usually symptom-led and we use the effect of refractive error on the visual acuity and other visual functions to decide whether a spectacle correction is necessary. In the majority of cases, when testing young children we are not using these criteria to manage refractive errors. We are using our understanding of normal visual and refractive development to identify children who are demonstrating abnormal patterns, and considering the impact of these abnormalities on their likely visual outcome. We’ve learnt from the research that the failure of emmetropization is related to poor visual outcome and that hyperopia retained beyond infancy dramatically increases the risk for strabismus and amblyopia. There is evidence from the research literature that glasses to correct or partially correct hyperopia may reduce this risk. The evidence is equivocal, with one study showing a decreased incidence of strabismus with early hyperopic correction, and another two showing improved visual acuity outcomes. However, several studies found no impact of spectacle correction. Atkinson and Braddick’s work showed that with spectacle correction for hyperopia, there was a reduction in risk to 4x for strabismus and 2.5x for amblyopia, from the 13x and 6x respectively they found when hyperopes were not corrected. There has been debate regarding whether prescribing glasses, even if it does improve visual outcomes, will impede the natural emmetropization process if glasses are given too early. Much debate is still ongoing in the research and clinical literature, but on balance there is not a great deal of evidence to support this idea. It would seem sensible, however, to wait until the most active stage of emmetropization is over – beyond 12 months of age – before prescribing glasses for hyperopic children in order to monitor whether emmetropization is active or failing. Figure 9.2 An examiner performing an objective refraction in a child There is some evidence that academic performance can also be hindered by uncorrected hyperopia and that uncorrected hyperopia discourages engagement with reading and may have implications for visuoperceptual skill development and aspects of cognitive, attention and motor skills in hyperopic children. Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-5  Refractive Development and Evidence-Based Prescribing CHILDREN NEEDING GLASSES To identify which children are failing to emmetropize, we either need to monitor their refractive development from early infancy, or we need to be able to identify older children whose refractive errors fall outside the normal range for their age. Figure 9.3 (a) An examiner performing an objective refraction in an infant Figure 9.3 (b) An examiner performing an objective refraction in a youngster Examination of the research literature suggests that the refractive errors listed in Table 9.2 can be considered significant in children of more than about 12-18 months of age. Some researchers have shown on repeated examination of infants and young children as SIGNIFICANT they age, that small but ‘significant’ astigmatic and anisometropic errors can be seen on REFRACTIVE ERRORS one visit and ‘disappear’ on the next. It may be important, therefore, for optometrists to (>12-18 MONTHS AGE) ensure that astigmatic errors and anisometropic errors are persistent before prescribing. However, it would seem appropriate to ensure that the practitioner does not assume such errors to be transient and ignore them for any length of time during the sensitive period. Perhaps a retest after two or three months would be appropriate in such cases. Table 9.2 Significant refractive errors Refractive error Magnitude Hyperopia >+3.50D in any meridian Hyperopia >+2.00D (children 4 years+) Persistent astigmatism > 1.50D Persistent anisometropia > 1.00D Myopia Any Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-6  Refractive Development and Evidence-Based Prescribing AMERICAN ACADEMY The American Academy of Ophthalmology takes a consensus based approach to identify OF OPHTHALMOLOGY what it considers refractive errors that warrant spectacle correction at 2-3 years of age GUIDELINES FOR (Table 9.3). Their web pages also give information relating to older children and can be PRESCRIBING a useful source of information, guidance and support for practitioners (2-3 YEARS) (www.aao.org/education/library/ppp/index.cfm) Table 9.3 Refractive error Magnitude Hyperopia (no tropia) > +4.50 D Hyperopia (with esotropia) > +1.50 D Astigmatism > 2.00 D Hyperopia > 1.50 D Anisometropia Myopia ≥ 2.00 D Astigmatism ≥ 2.00 D Myopia > −3.00 D When making prescribing decisions, it is important not just to use refractive error data, but to consider aspects of vision, visual function and general and intellectual development (Fig. 9.4). In particular, the use of objective measures of accommodative facility with techniques such as dynamic retinoscopy, and careful measures of visual acuity at distance and near should be used to help make decisions about prescribing. However, one cannot avoid the suggestion from the evidence that significant hyperopic, astigmatic and anisometropic refractive errors as outlined above, increase the risk of DECIDING THE poor visual outcome and provision of spectacle correction may improve this risk. PRESCRIPTION For example, little benefit from a hyperopic correction is expected for a three-year-old with moderately hyperopic refractive error, accurate accommodation, well compensated exophoria and excellent, age-appropriate monocular acuities. By contrast, significant benefit from a full hyperopic correction is expected from another three-year-old with the same refractive error (as above), significant accommodative lag and poorly compensated esophoria. Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-7  Refractive Development and Evidence-Based Prescribing Figure 9.4 Performing various investigations to check visual functions and intellectual development AMOUNT OF PRESCRIPTION When we have decided that a spectacle prescription is warranted, the practitioner needs to decide on the level of error to correct. Whilst there are limited data to provide evidence for best practice in this area, the following guidelines can be applied. In particular, giving the full anisometropic difference and the full hyperopic correction in the presence of strabismus is important. Results of recent large multicentre studies of amblyopia treatment have shown that the optimal treatment for amblyopia begins with spectacle correction and that the improvement in visual acuity seen as a result of this spectacle wear should be monitored until it plateaus at two consecutive visits (two months apart). It may take up to eight months of spectacle wear for the full effect of this aspect of treatment to take effect. It is important when prescribing glasses that the effect of the spectacles, the compliance with them and future visual development is closely monitored. It is also very important that appropriately fitting glasses with plastic lenses are used. Taking age, history and other clinical findings and observations into consideration, prescribe:  Full astigmatic correction  Full anisometropic correction  Partial correction of hyperopia on first prescription (leave 1D under corrected), and follow-up  Full correction of hyperopia when strabismus present  Full myopic correction Dec 2012, Version 1-1 Peadiatric Optometry, Chapter 9-8