Ophthal Prysol Cpt 2004 24:458-463 Clinical characteristics of unilateral myopic anisometropia in a juvenile optometric practice population Jonathan S.Pointer'and Bernard Gilmartin Oplometric Research,4A Market Square.Higham Ferrers,Northants NN10 BBP,and"Nour. sciences Research Insttute.Aston University.Brmingham,UK Abstract Papase:A retraspecthve study at longitudinal case historins,undartakan to estahlsh the clinical and statistical characteristcs of unilsteral myupic anisometropia (UMA)amongst the juvenie and adolescent population at an optometric practice,is reported.UMA was detined as that specfc reractive state where an unequivocaly myopic eye is paired with a plano'[apherical equivalent retmacion.(SER)=+0.25 Dioptrs (D]]companion ay8. Methods:The dnical records of al pabents aged 0.1)to that fitied to the ametropic progression roccrdod in eithor cye of the case-maldhod population of young biateral myopes uniquety the slpe associaled with the comparion eye of UMA cases was statistcaly signincamy (p<05)leas stesp Compered wih bilateral myopes tawer cases of UMA required a refrartwe correction to releve visusl or asthencpic symptoms,and this intial oorrection was dsponsed on average 1 yoar later (at age 12.7 years)in UMA pationts. Conusions:Indiidusis identifed as demorstrating dinicaly-defined UMA can be considered as distinc hut functorally normal cases on the continum of human refractiva amor.Howaver,Any unilaterahy-actng deteminng fattor(s)underying the geness of the conditon remain cbsoure. Keywords:adalescont,juverile,myopia.optometric practice populsnon,unilataral myoplc anisometrop Introduction condition under evaminntion here unilateral myopic anisometropia (UMA)is that situation where an Anisometropia,by detinition,exists whenever a ditfer- unequivocally myopic ey增i5 paired wil凸one baving ence in refractive status is present between an individ- plano refraction. ul's pair of eyes.Any refractive comhination and The existence of any determining factors)for degree of imbalance is possible:the specific clinical anisometropia remains cbcure.A genetic hasis is a possibility (Sorsby.1972).although for low degrees Recvited.I$Jauuy 2004 (eg.1.00 D)and in isolnted cases (ie.where no other Rerood furnt 23 April 2004 Camily members ure affected)tbe coodition can be deoponf 6 May 2004 regarded as sporadie (Lyk.1990).Specifically in myopic cases,it is recognised that it is the relative axial length of ararpudnre d nprhu regans to1.发rrr I-mil ardresc jonathin pointenievirgin net the posterior virreous chnmber that constirutes the 458 2004 Tho Colege of Opsnorists
Clinical characteristics of unilateral myopic anisometropia in a juvenile optometric practice population Jonathan S. Pointer1 and Bernard Gilmartin2 1 Optometric Research, 4A Market Square, Higham Ferrers, Northants NN10 8BP, and 2 Neurosciences Research Institute, Aston University, Birmingham, UK Abstract Purpose: A retrospective study of longitudinal case histories, undertaken to establish the clinical and statistical characteristics of unilateral myopic anisometropia (UMA) amongst the juvenile and adolescent population at an optometric practice, is reported. UMA was defined as that specific refractive state where an unequivocally myopic eye is paired with a plano [spherical equivalent refraction, (SER) ¼ ±0.25 Dioptres (D)] companion eye. Methods: The clinical records of all patients aged 0.1) to that fitted to the ametropic progression recorded in either eye of the case-matched population of young bilateral myopes; uniquely the slope associated with the companion eye of UMA cases was statistically significantly (p < 0.025) less steep. Compared with bilateral myopes fewer cases of UMA required a refractive correction to relieve visual or asthenopic symptoms, and this initial correction was dispensed on average 1 year later (at age 12.7 years) in UMA patients. Conclusions: Individuals identified as demonstrating clinically-defined UMA can be considered as distinct but functionally normal cases on the continuum of human refractive error. However, any unilaterally-acting determining factor(s) underlying the genesis of the condition remain obscure. Keywords: adolescent, juvenile, myopia, optometric practice population, unilateral myopic anisometropia Introduction Anisometropia, by definition, exists whenever a difference in refractive status is present between an individual’s pair of eyes. Any refractive combination and degree of imbalance is possible: the specific clinical condition under examination here – unilateral myopic anisometropia (UMA) – is that situation where an unequivocally myopic eye is paired with one having a plano refraction. The existence of any determining factor(s) for anisometropia remains obscure. A genetic basis is a possibility (Sorsby, 1972), although for low degrees (e.g. <1.00 D) and in isolated cases (i.e. where no other family members are affected) the condition can be regarded as sporadic (Lyle, 1990). Specifically in myopic cases, it is recognised that it is the relative axial length of the posterior vitreous chamber that constitutes the Received: 15 January 2004 Revised form: 23 April 2004 Accepted: 6 May 2004 Correspondence and reprint requests to: J. S. Pointer. E-mail address: jonathan.pointer@virgin.net Ophthal. Physiol. Opt. 2004 24: 458–463 458 ª 2004 The College of Optometrists
Juvenile unilateral myopic anisometropia:J.S.Pointer and B.Gilmartin 459 primary physical basis for the inter-eye refractive second group of n=21 individual case histories was imbalance (Sorsby et al.,1962:Logan er af..19951. assembled.Selction for this group was on a case- Unfortunately,with the possible exception of two matched basis (gender.age,and magnitude of the studies on the prevalence of anisomelropia in school refraction in the more-myopic eye)against the same chaldren (Parssinen.1990)and adults (Weale.20021. characteristics of'tbe w 21 UMA patients. statistics relating to the distribution of the several There was no clinical diflerence between the Snellen varieties of anisometropia tend to be confused or even acuity of the two eyes of these unilaterally and bilater- contrudictory (for example,see Iirsch.1967,and the ally myopic individuals.For either eye it was recorded as literature surveys of Duke-Elder and Abrams,1970.and being at least 6/9 (with a refraclive correction if Laird,1991).Much of this uncertainty can be attributed necessary),the majority attaining 6/6 or better in their cither to n lack of agreement on the criterion to be pre-teen and adolescent years. adopted for the inter-ocular refractive difference taken The distance and near ccnlo-motor balance of all to define 'anisometropia'or to the decision on whether individuals in these two study groups was recorded as or not to include pathological or amblyopic cases in the being within normal clinicul limits at each of their sight study population. tests,with no evidence of amhlyopin or manifest ocular As a precursor to another study,a retrospective devintion:standard screening with the Lang Stereotest analysis of longitudinal soquences of refractive case lI at 40 cm had also indicated stereopsis better than records was undertaken to document the clinical char- 200s are in all individuals at their initial cye examina- acteristics and natural history'of UMA in a juvenik Lion at the practice.The gender.age and refractive and adolescent oplometric population details of all subjects were entirely pon-attribulable in subscquent analysis thus preserving patient confidenti- Methods alty. The clinical likes at an independent optometric practice established for nearly 15 years were surveyed in the late Results and anal少ys summer of 2003.The refraction records of all palients For either group,for each of the a-2I contributing (Caucasian)who were aged <19 years (typicully ahout cuses,longitudinal refructive history was avuilahle 25%of the practice's patient hase)were identified, from the clinical rooords.The mean S.D.(standard producing a total of 724 case histories.The upper age deviation)number of sight tests was 5.67t 3.02 per limit was spacified because the refraction should have UMA paulient and 5.14 2.24 per bilateral myope: stahilised in the majority of individuals by the mid-to the mean interval hetween examinations was late teens (Goss and Winkler,1983).Refructive correc- I.l6±0.67 years for UMA cases and1.l3± tions were maximally+600 DS with astigmatism no 0.59 years for the bilateral myopes. ereater than -2.00 DC. The refractive material of the UMA patients.sum- All refractions had boen undertaken in the same test marisod as the inter-ocular retractive differenoe ASER location by author JSP.Routine non-cycloplegic proce- =consistently myopxc eye SER mimas (initially)plano dures were the norm,using a standard spectacle trinl companion eye SER,D].is displayed vs patient age in lens set graded in 0.25 D intervals to nchieve best Figwre fa.The point where each of these subjects first subjoctrve acuity on the Snellen chart at 6 m:the met the spocific clinical definition of UMA adopted here refraction end-point was moritored using the duo- is indicated by a circular symbol.The mean age when chrome test to achieve eguality or a just-on-red bias. UMA was first identified in this group was Based on an overview of'their available series of 12.37±227ea3:52.1%(n=110f21)ofh×cases bilateral refractions.these juvenile and adolescent indi emerged between the ages of 11.5 and 13.5 years,with viduals were classified as fallkox:'myopic'(spherical the remainder arising in equal numbers before and after equivalent refraction.(SER)S-0.50 D:146 or 20.2%of this 2-year span. cases).'hypermetropic'(SER2+0.75 D:72 or 9.9%)and The availability of these series (n 21)of refractive emmetropic'(SER 2-0.37st 0.62 D:506 or 69.9%). histories alo permilted a cross-sectional investigation of Within the myopic refractive classification a-21 any ige-related refractive trend in this material The indiviluals (14.4%or uround I-in-7 of the juvenile clculation (after Harris,1991)was undertaken of the myopes)were,at two ar more consecutive examinations. mean of ench set of sphero-cylindrical prescriptians myopic in one eye and 'plano'(SER -+0.25 D)in ncross all avnilable individunls of a given age (incre. their companion cye:this group of case histories bocame ments of I year:26<19 years):also the mean SER was the clinically-defined population of UMA cases.The stablished across contributing prescriptions for both remainder of the myopie classificntion recorded consis. the myopie and the companion eyes at each age tent bilateral ametropia:from this pool of material a grouping.The results of this procedure are given in e2004 The Colloge of Opomatists
primary physical basis for the inter-eye refractive imbalance (Sorsby et al., 1962; Logan et al., 1995). Unfortunately, with the possible exception of two studies on the prevalence of anisometropia in school children (Pa¨rssinen, 1990) and adults (Weale, 2002), statistics relating to the distribution of the several varieties of anisometropia tend to be confused or even contradictory (for example, see Hirsch, 1967, and the literature surveys of Duke-Elder and Abrams, 1970, and Laird, 1991). Much of this uncertainty can be attributed either to a lack of agreement on the criterion to be adopted for the inter-ocular refractive difference taken to define anisometropia or to the decision on whether or not to include pathological or amblyopic cases in the study population. As a precursor to another study, a retrospective analysis of longitudinal sequences of refractive case records was undertaken to document the clinical characteristics and natural history of UMA in a juvenile and adolescent optometric population. Methods The clinical files at an independent optometric practice established for nearly 15 years were surveyed in the late summer of 2003. The refraction records of all patients (Caucasian) who were aged <19 years (typically about 25% of the practice’s patient base) were identified, producing a total of 724 case histories. The upper age limit was specified because the refraction should have stabilised in the majority of individuals by the mid-tolate teens (Goss and Winkler, 1983). Refractive corrections were maximally ±6.00 DS with astigmatism no greater than )2.00 DC. All refractions had been undertaken in the same test location by author JSP. Routine non-cycloplegic procedures were the norm, using a standard spectacle trial lens set graded in 0.25 D intervals to achieve best subjective acuity on the Snellen chart at 6 m: the refraction end-point was monitored using the duochrome test to achieve equality or a just-on-red bias. Based on an overview of their available series of bilateral refractions, these juvenile and adolescent individuals were classified as follows: myopic (spherical equivalent refraction, (SER) £)0.50 D: 146 or 20.2% of cases), hypermetropic (SER ‡+0.75 D: 72 or 9.9%) and emmetropic (SER ‡)0.37£+0.62 D: 506 or 69.9%). Within the myopic refractive classification n ¼ 21 individuals (14.4% or around 1-in-7 of the juvenile myopes) were, at two or more consecutive examinations, myopic in one eye and plano (SER ¼ ±0.25 D) in their companion eye: this group of case histories became the clinically-defined population of UMA cases. The remainder of the myopic classification recorded consistent bilateral ametropia: from this pool of material a second group of n ¼ 21 individual case histories was assembled. Selection for this group was on a casematched basis (gender, age, and magnitude of the refraction in the more-myopic eye) against the same characteristics of the n ¼ 21 UMA patients. There was no clinical difference between the Snellen acuity of the two eyes of these unilaterally and bilaterally myopic individuals. For either eye it was recorded as being at least 6/9 (with a refractive correction if necessary), the majority attaining 6/6 or better in their pre-teen and adolescent years. The distance and near oculo-motor balance of all individuals in these two study groups was recorded as being within normal clinical limits at each of their sight tests, with no evidence of amblyopia or manifest ocular deviation: standard screening with the Lang Stereotest II at 40 cm had also indicated stereopsis better than 200 s arc in all individuals at their initial eye examination at the practice. The gender, age and refractive details of all subjects were entirely non-attributable in subsequent analysis thus preserving patient confidentiality. Results and analysis For either group, for each of the n ¼ 21 contributing cases, a longitudinal refractive history was available from the clinical records. The mean ± S.D. (standard deviation) number of sight tests was 5.67 ± 3.02 per UMA patient and 5.14 ± 2.24 per bilateral myope: the mean interval between examinations was 1.16 ± 0.67 years for UMA cases and 1.13 ± 0.59 years for the bilateral myopes. The refractive material of the UMA patients, summarised as the inter-ocular refractive difference DSER [¼consistently myopic eye SER minus (initially) plano companion eye SER, D], is displayed vs patient age in Figure 1a. The point where each of these subjects first met the specific clinical definition of UMA adopted here is indicated by a circular symbol. The mean age when UMA was first identified in this group was 12.37 ± 2.27 years: 52.4% (n ¼ 11 of 21) of these cases emerged between the ages of 11.5 and 13.5 years, with the remainder arising in equal numbers before and after this 2-year span. The availability of these series (n ¼ 21) of refractive histories also permitted a cross-sectional investigation of any age-related refractive trend in this material. The calculation (after Harris, 1991) was undertaken of the mean of each set of sphero-cylindrical prescriptions across all available individuals of a given age (increments of 1 year: ‡6<19 years): also the mean SER was established across contributing prescriptions for both the myopic and the companion eyes at each age grouping. The results of this procedure are given in Juvenile unilateral myopic anisometropia: J. S. Pointer and B. Gilmartin 459 ª 2004 The College of Optometrists
480 Op/thal.Physiol.Opt.2004 24:No.5 Table and are illustraled in Figure 16.The broad pallern between the lwo eyes is striking.with the eye picture is of an increasingly neglive (i.e.myopic) that was initially approxximately plano (unflled symbols refractive trend in either eye across the 13 year age in Figure Ib)itself hecoming myopie with advancing span studied.An initial steady rise is checked hriefly adolescence hut at a kxsser rate and to n lower degree around the age of 9-10 years,before continuing at a than its continuously myopic companion eye (solid steeper rale for a couple of years before that increase is symbols). also reined in,subsequenily to be maintained al a Regression analysis provided good linear fits (dashed plateau from the mid-teens onwards.The similrity of lines)to these series of age-related refractive data: -150 10 -00 +050. -1.20 -.50 20 4Q50 作=21 +120 11121314561718 AOE yoars) Figure 1.Ago-related mfactve trands ofo=21 unilateral myopic anisomotopes (UMA)agod from 6 to 19 yoars of age.(a)Lorgboudinal data: individusl bubjedts'age ve ntur-ocular tutactive ditlerence,SSER [-consistentty myupic eye SER mnus (intal plsno companion eye SEH: Dioptres (U.Groula symbols ind cate the point where he SER of indidual putents hrst met the clinical detrnon at UMA adopled in this shudy. A tolal of 52.4%(11 of 21]af these poimts ocour between 11.5 and 13.5 years (age span indicaled by the horzomal double-ended artow at the top centre of the figure)()Cross-sectional datar group averape age (Tacle I]vs mean SER (D)of coreistently myopic eye (solid square symbok and dehed mogreasion line:y=060-0.10=-094 =0.B8)And ccmpanion ay (uniled square symbol and dahed ragrassian lira:y=0.56-0.06xr=-091 =0831.In adison Pe Ingar tor asion fita (aoliso the Aga-relenad mean ralractia trand of the most myopic eye(M:y =055 -0 08xr=-083=088)and of the l mepe:m15y=053-00期x,r=-09p,7=0A5周2rA case-malched (=21)el mypes ()see Table 1.Age-relsted mean (tansverse)retractive error (cakculation methodology atter Hams,1991)of consistentty myopic eye and (ntislly) plsno'companion eye of n -21 unilaterl myopi anisometropes Mean refroctlve error "Plano'cye Myoplc cye Agn0naan。g.D.】Subjnc(n Sph(D] CyD可 Ax线 SER (D) Sph (D) Gylo的 Axia gEnD列 6.33±0.35 2 +0.50 -025 90.0 0.39 +025 -Q25 90.0 0.12 7.40±022 4 +Q12 -0.12 90.0 +Q.05 -001 Q11 75.0 -0.0e 851+028 -004 -0.09 81.1 -08 -021 -012 101,7 -027 940+028 少 +00 -014 4.7 -003 -02 -007 785 -08 1034±021 10 000 -0.2 1154 -001 -029 -006 113.6 -032 1140±029 11 -020 -0.04 H7H -D22 -057 -06 979 -1 1240±0.32 14 026 -0.14 108.1 Q.33 081 0.15 72.2 088 1327±0.17 9 014 0.03 831 015 058 g0.0 062 14.26主0.22 12 Q33 -0.17 1005 041 -096 013 753 -102 1523主0.33 14 -041 -0.08 104.1 045 -006 -008 75.0 -100 1634±030 -040 -006 90.9 -0.43 -10e Q.02 5.0 -10g 1732±0.33 10 -027 -0.12 936 -033 -0.94 -Q10 104.5 -0附 1833±0.37 5 Q.55 -0.05 100.1 Q.57 -101 Q.02 120.0 -10 Sph,spherical;Cy,cyindrical:SER,spheroal oquivalant retmction
Table 1 and are illustrated in Figure 1b. The broad picture is of an increasingly negative (i.e. myopic) refractive trend in either eye across the 13 year age span studied. An initial steady rise is checked briefly around the age of 9–10 years, before continuing at a steeper rate for a couple of years before that increase is also reined in, subsequently to be maintained at a plateau from the mid-teens onwards. The similarity of pattern between the two eyes is striking, with the eye that was initially approximately plano (unfilled symbols in Figure 1b) itself becoming myopic with advancing adolescence but at a lesser rate and to a lower degree than its continuously myopic companion eye (solid symbols). Regression analysis provided good linear fits (dashed lines) to these series of age-related refractive data: –2.00 0 10 11 12 13 14 15 16 17 AGE (years) Mean SER (D) ∆SER (D) a b –1.50 –1.00 –0.50 +0.50 –1.00 –0.50 +0.50 +1.00 6 7 8 9 18 n = 21 M L Figure 1. Age-related refractive trends of n ¼ 21 unilateral myopic anisometropes (UMA) aged from 6 to 19 years of age. (a) Longitudinal data: individual subjects age vs inter-ocular refractive difference, DSER [¼consistently myopic eye SER minus (initially) plano companion eye SER: Dioptres (D)]. Circular symbols indicate the point where the SER of individual patients first met the clinical definition of UMA adopted in this study. A total of 52.4% (n ¼ 11 of 21) of these points occur between 11.5 and 13.5 years (age span indicated by the horizontal double-ended arrow at the top centre of the figure). (b) Cross-sectional data: group average age (Table 1) vs mean SER (D) of consistently myopic eye (solid square symbols and dashed regression line: y ¼ 0.60 ) 0.10x, r ¼ )0.94, r 2 ¼ 0.88) and companion eye (unfilled square symbols and dashed regression line: y ¼ 0.56 ) 0.06x, r ¼ )0.91, r 2 ¼ 0.83). In addition the linear regression fits (solid) to the age-related mean refractive trend of the most myopic eye (M: y ¼ 0.55 ) 0.09x, r ¼ )0.93, r 2 ¼ 0.86) and of the least myopic eye (L: y ¼ 0.53 ) 0.08x, r ¼ )0.92, r 2 ¼ 0.85) for a case-matched population (n ¼ 21) of bilateral myopes (see text) are shown. Table 1. Age-related mean (transverse) refractive error (calculation methodology after Harris, 1991) of consistently myopic eye and (initially) plano companion eye of n ¼ 21 unilateral myopic anisometropes Age [(years) mean ± S.D.] Subjects (n) Mean refractive error ‘Plano’ eye Myopic eye Sph (D) Cyl (D) Axis SER (D) Sph (D) Cyl (D) Axis SER (D) 6.33 ± 0.35 2 +0.50 )0.25 90.0 +0.38 +0.25 )0.25 90.0 +0.12 7.40 ± 0.22 4 +0.12 )0.12 90.0 +0.06 )0.01 )0.11 75.0 )0.06 8.51 ± 0.26 6 )0.04 )0.09 81.1 )0.08 )0.21 )0.12 101.7 )0.27 9.40 ± 0.26 8 +0.04 )0.14 94.7 )0.03 )0.32 )0.07 78.5 )0.35 10.34 ± 0.21 10 0.00 )0.02 115.4 )0.01 )0.29 )0.06 113.6 )0.32 11.40 ± 0.29 11 )0.20 )0.04 91.8 )0.22 )0.57 )0.06 97.9 )0.60 12.40 ± 0.32 14 )0.26 )0.14 108.1 )0.33 )0.81 )0.15 72.2 )0.88 13.27 ± 0.17 9 )0.14 )0.03 83.1 )0.15 )0.58 )0.08 90.0 )0.62 14.26 ± 0.22 12 )0.33 )0.17 100.5 )0.41 )0.96 )0.13 75.3 )1.02 15.23 ± 0.33 14 )0.41 )0.08 104.1 )0.45 )0.96 )0.08 75.0 )1.00 16.34 ± 0.30 11 )0.40 )0.06 90.9 )0.43 )1.02 )0.02 85.0 )1.03 17.32 ± 0.33 10 )0.27 )0.12 93.6 )0.33 )0.94 )0.10 104.8 )0.99 18.33 ± 0.37 5 )0.55 )0.05 100.1 )0.57 )1.01 )0.02 120.0 )1.02 Sph, spherical; Cyl, cylindrical; SER, spherical equivalent refraction. 460 Ophthal. Physiol. Opt. 2004 24: No. 5 ª 2004 The College of Optometrists
JJuvenile unilateral myopic anisametropia:J.S.Painter and B.Gilmartin 461 myopie eye0y-0.60-0.10x.r--0.94,r'-0.88 -0.18×89.62and-0.79-0.l6×81.52 for the greater and companion eye (y -0.56-0.06x,--0.91. and lesser myopic eyes,respectively. -0.83).Also shown on Figure are the linear In 57.1%(12 of 21)of ITMA cases the left eye regression fits (lightly dotted lnes)to the ape-related was the consistently (more)myopic one.The laterality refructive trends of each eye of the case-matched distrihution of the more-myopic eye in the bilaterally bilaterally myopic population:most myopic eye ('M': myopic patients was similar to that found for the UMA y-0.55-0.09xr--0.93,≥2-0.80 and le1stmy cases,namely the left eye in 61.9%of cases (n-13 of pic eye (Ly-0.53-0.08xF--0.92,2-0.85 212-0,1GP-0,75. Nonparametric statistical testing (Kolmogorov-Smir- Female UMA cases (n=16 of 21:76.2%)greatly nov)confirmed that the dependent variable SER was outnumberod males.This gender imbalance of 3:1 is normally distributed in all of'this material.Conse- substantially larger than the 22%female exoess (i.e. quently the same statistical technique (twe-smpl 55%of patients)fourd across all patients aged testing)was then employed to assess the extent of any 19 years at this optometric prnctice.and is a differenoe between the individual lincar fits to these four statistically significant feature (=9.76:p=0.002). sets of age-relted refractive material. In this regard it maght be remarked that to case-match The linear gradient litting the distribution of the individuals between the uni-and bilaterally myopic (initially)plano companion eye of the UMA cases was patient groups,the marked (3:1)female gender bias shown to be slatistically signifcanlly diflerent lo the uncovered in the UMA subjecis had to be suslained in slopes fitting the other three classes p0.025 vs myopic the bilaterally myopic comparison group.While a UMA eye data or moost myopic eye data of the bilaterully female bias in optometric patient numbers is a feature myopic matebed cases:p 0.03 vs least myopic eye dala which has been remarked upon previously (Pointer, of the bilaterally matcbed cuses.Iowever,no statislically 1996,2000)-and was indeed manifest at this practice significant difTerence was indicuted between the linear it must be acknowledged that this imbalance may have regression gradient through the myopic UMA eye data had an influence on the absolute refractive and other and that through either the most or the lenst myopic eye of values derived here for these clinical comparisans the hilaterally myopic population:p>0.1 in each between divisions of the myopic classification. instance.In addition.there was no statistically signincant ditferenoe (p 0.1)between the slopes fitting the two Discussion eyes of the hilaterlly myopic cases. The clinical impression stated ahove is thus substan- On the hasis of the analysis of the clinical materal tiated statistically:the (initially)plano companion eye in nssembled here.it seems reasonable to suepest that cases UMA cases docs indood manifest a uniquely lesser of UMA can be regarded as a subset of bilateral myopia. average rate of myopic chanee with increasing age.not More specifically.ametropia in the consistently myopic only in comparison to its fellow consistently myopic eve eye of juvenile UMAs progresses at a similar rate to that but also vs the age-related refractive trend in visually observed in visually normal young blateral myopes. normal bilaterally myopic patients. whereas the (initially)plano eye shows a lesser myopic Reviewing other comparative clinical aspects of the change with advarxing age. two juvenile myopic optometric populations.it was This clincally-derived conclusion fits well with the found that overall two-thirds (n=14 of 21)of the sparse anato-physiologial evidence available with UMA patients rexquired a refractive correction hefore regard to anisometropia.The consensus is that a the age of 19 years for the relief of visual/asthenopic structural difference underpins the myopic inter-ocular symptoms.The mean age at which this first correction imhalance,the refructive difference heing correlated was dispensed was 12.72 3.12 years:at this point the with an inter-plohe difference in axial length of the mean prescription (methodology after Harris,1991) posterior vitreous chamber (Sorsby et al.,1962:Flodel- across the myopic eyes was -0.87/-0.12 x 78.35 and for ius,1981:Logan er al.,1995;Choi er al.,2003),an the companion eyes wis -0.15/-0.16 x 86.29.Com- independent change (increase)in the coreal power pared with the UMA cases,a much larger proportion being most unlikely (Ooi and Grosvenor,1995;Zadnik (90.5%:w=19 of 21)of the hilaterally-myopic patients erw.,2003 with the CLEERE Study Group).In requirod a refractive correction before the age of nddition.inter-ocular differences in fundus morphology 19 years.While clinically signitcant.this ditference in lincluding the presenoe of opte dise crescents and prescribing rate was only of borderline statistical sign- increased tessellation:Curtin and Karlin.1971)are often ficance (y 3.53:p 0.06).The mean age at which present.underlining the anatomical basis advanced to this first prescription was dispensod was exactly I year nccount for the anisomyopic condition. in advance of the UMA patients.being However.the enduring paradox centres on why it is 11.70+2.80 years.The mean prescription was -0.95/ that anisometropia (especially in its more extreme forms) 金2204 The Cullye ol Op2 uTNhab
myopic eye (y ¼ 0.60 ) 0.10x, r ¼ )0.94, r 2 ¼ 0.88) and companion eye (y ¼ 0.56 ) 0.06x, r ¼ )0.91, r 2 ¼ 0.83). Also shown on Figure 1b are the linear regression fits (lightly dotted lines) to the age-related refractive trends of each eye of the case-matched bilaterally myopic population: most myopic eye (M: y ¼ 0.55 ) 0.09x, r ¼ )0.93, r 2 ¼ 0.86) and least myopic eye (L: y ¼ 0.53 ) 0.08x, r ¼ )0.92, r 2 ¼ 0.85). Nonparametric statistical testing (Kolmogorov–Smirnov) confirmed that the dependent variable SER was normally distributed in all of this material. Consequently the same statistical technique (two-sample testing) was then employed to assess the extent of any difference between the individual linear fits to these four sets of age-related refractive material. The linear gradient fitting the distribution of the (initially) plano companion eye of the UMA cases was shown to be statistically significantly different to the slopes fitting the other three classes: p 0.1 in each instance. In addition, there was no statistically significant difference (p > 0.1) between the slopes fitting the two eyes of the bilaterally myopic cases. The clinical impression stated above is thus substantiated statistically: the (initially) plano companion eye in UMA cases does indeed manifest a uniquely lesser average rate of myopic change with increasing age, not only in comparison to its fellow consistently myopic eye but also vs the age-related refractive trend in visually normal bilaterally myopic patients. Reviewing other comparative clinical aspects of the two juvenile myopic optometric populations, it was found that overall two-thirds (n ¼ 14 of 21) of the UMA patients required a refractive correction before the age of 19 years for the relief of visual/asthenopic symptoms. The mean age at which this first correction was dispensed was 12.72 ± 3.12 years: at this point the mean prescription (methodology after Harris, 1991) across the myopic eyes was )0.87/)0.12 · 78.35 and for the companion eyes was )0.15/)0.16 · 86.29. Compared with the UMA cases, a much larger proportion (90.5%: n ¼ 19 of 21) of the bilaterally-myopic patients required a refractive correction before the age of 19 years. While clinically significant, this difference in prescribing rate was only of borderline statistical signi- ficance (v2 ¼ 3.53; p ¼ 0.06). The mean age at which this first prescription was dispensed was exactly 1 year in advance of the UMA patients, being 11.70 ± 2.80 years. The mean prescription was )0.95/ )0.18 · 89.62 and )0.79/)0.16 · 81.52 for the greater and lesser myopic eyes, respectively. In 57.1% (n ¼ 12 of 21) of UMA cases the left eye was the consistently (more) myopic one. The laterality distribution of the more-myopic eye in the bilaterally myopic patients was similar to that found for the UMA cases, namely the left eye in 61.9% of cases (n ¼ 13 of 21): v2 ¼ 0.10; p ¼ 0.75. Female UMA cases (n ¼ 16 of 21: 76.2%) greatly outnumbered males. This gender imbalance of 3:1 is substantially larger than the 22% female excess (i.e. 55% of patients) found across all patients aged <19 years at this optometric practice, and is a statistically significant feature (v2 ¼ 9.76; p ¼ 0.002). In this regard it might be remarked that to case-match individuals between the uni- and bilaterally myopic patient groups, the marked (3:1) female gender bias uncovered in the UMA subjects had to be sustained in the bilaterally myopic comparison group. While a female bias in optometric patient numbers is a feature which has been remarked upon previously (Pointer, 1996, 2000) – and was indeed manifest at this practice – it must be acknowledged that this imbalance may have had an influence on the absolute refractive and other values derived here for these clinical comparisons between divisions of the myopic classification. Discussion On the basis of the analysis of the clinical material assembled here, it seems reasonable to suggest that cases of UMA can be regarded as a subset of bilateral myopia. More specifically, ametropia in the consistently myopic eye of juvenile UMAs progresses at a similar rate to that observed in visually normal young bilateral myopes, whereas the (initially) plano eye shows a lesser myopic change with advancing age. This clinically-derived conclusion fits well with the sparse anato-physiological evidence available with regard to anisometropia. The consensus is that a structural difference underpins the myopic inter-ocular imbalance, the refractive difference being correlated with an inter-globe difference in axial length of the posterior vitreous chamber (Sorsby et al., 1962; Fledelius, 1981; Logan et al., 1995; Choi et al., 2003), an independent change (increase) in the corneal power being most unlikely (Ooi and Grosvenor, 1995; Zadnik et al., 2003 with the CLEERE Study Group). In addition, inter-ocular differences in fundus morphology (including the presence of optic disc crescents and increased tessellation: Curtin and Karlin, 1971) are often present, underlining the anatomical basis advanced to account for the anisomyopic condition. However, the enduring paradox centres on why it is that anisometropia (especially in its more extreme forms) Juvenile unilateral myopic anisometropia: J. S. Pointer and B. Gilmartin 461 ª 2004 The College of Optometrists
462 Oplwral Physiol.Opt.2004 24:No.5 should arise in a pair of eyes that have presumably progression documented in the (initially)plano eye of hitherto experienced the same environmental,hormonal such individuals compared with not only the trend and nutritional conditions.While it may be reasonable to obeerved in the consistently myopic companion eye but postulate that a difTerence in the rate of emmetropisation also to that recorded in visually normal bilaterally may account for anisomyopia in an infant,this explan. myopic young persons. ation is surely untenable in the context of a healthy and The clinical evidence discussed here implies that cases visually Dormal adolescent wbo first manifests UMA of UMA should be regarded as a subset of the myopic when (s)he enters the second decade of life. population.ie.as funclionally normal but distinct It is dinicult to contemplate any exclusively unilateral points on the continuum of human refractive error. nfluenoe or bias affecting agroed and accepted consen- Either eye,but spocifically that which manifests consis- sual ncuro-physiological processes.Thus.for exnmple tent myopia,d iplnys refractive and other characteristics the possibility of any unilaterally-directed increase in typical of a visually normal developing myopic eyr.This parasympathetic or sympathetie activity or tone specif- latter observation would promote the utilisation of such cally at the level of the ciliary body would be most clinically-distinct individuals in prospectrve tnals de- difficnlt to reconcile with the known facts regarding siened to interrupt or retard the propression of human function of'the autonomic nervous system (see Gilmar- myopia.Any treatment applied to an approximately tin,1998).An investigution of tonic accommodation for 'plano'eye which corcurrently acted as in inherent possibly of pupillary function)in a defined group of control for its fellow myupic eye would have obvious UMA subjects might give the lie to such suggestions. experimental ulility in trials employing either oplical Animal studies have sugpested that direct spatially- (bi-/multifocal spectacle lenses:Gwiazda er af..2003). locul retinal-scleral communication regulates axial assumed-physical (rigid gus-permeahle contact lenses: length of the globe.In this regard,Norton and Siegwart Walline et af.,2001)or pharmacological [e.g.Pirene (1995)have speculated that if such a neural linkage is pine (a relatively selective MI-muscarinic antagonist) present in man.successful childhood emmetropisation 2%ophthalmi gel b.i.d.:Tan et af..2003:Siatkowski must involve not only an intact and functional emme- er af..2004]therapeute methods of inhibiting myopic tropisation mechanism bat abo puarantecd exposure to progression. n non-compromised visual environment.Again,the assumption is that any external influence will be hilateral Referenees and that any internal cffect will invanably affect the neuro-physiology of hoth eyes. Chai,5.5 Gxrner,I.F.and Fnoch,J.M.(2003]Stile- It is similarly difficult to envistge hereditary influen- Crawford effect o the first kind (SCE-1)in poet-photore ces having anything other than a bilateral effect upon fractive koraloctomny and anisomctropic subjocts Oshmal. refractive develpmenL.Edwards (1998)has speculated w1.0pr.23.423476. that there might be '..a genetic programming which Curtin,B.J.and Kartin,D.B.(1971)Axial kngth measure- anects the two eyes dinerently.or which affocts the ments and fandus changes o the myopc eye.Am.J. susoeptibality of the two eyes to some environmental hh和W7I.47-53. Dake-Eef、W,S.nd Ahrais D.I97S知y factorfs)differently'.It remains to be seen whether the Ophthainlogy.Val.V.Opluiumic Optics amd Refraction, burgeoning genetic research directed at the decoding of H.ry Kimplen,Landon、UK the human genome throws any light on this specific Edwards.M.H.(1998)Myopia definitions.classifications and developmental conundrum.However,with regard to the ccomomic implications.In:Mypis and Nranak (ads M. clinical material presented here,it muist be remembered Rosentield and H.Gilmartinl.Batterworth Heiremann. that a substantial proportion of DMA cases emerge not Oxford.UK.pp.7. in infincy but in young persons entering adokscence Fedelius,H.C.(1981)Refractive components in aniso-and (refer to Figure aj. isometropi In:Docamenra Oplunolofoyla Prorredngs Seris No.29 (eds H.C.Fledelius,P.H.Alshirk and E. Cioldschaadt).Dr W.Junk,Holland,pp.8-95. Cunclusions Gilmeirtin,B.(19%8)Aulonumie:cornelles uf near-vison in emmetropia and myopia.In:Myupin and Nrrurk feds Defining UMA as a myopic vs a plano refraction.the M.Roenficld and B.Gilmartin).Batterworth-Heieemann. incidence of this specilic refraclive lype amongst healthy Oxford,UK.pp.117 146. and normally-sighted optometric patients aged Goes.D.A.and Winkler.R.L.(1933)Progression of myopia ≤193ear8wa52%【which pr0p00n0冈tdo in youth:age of cessaton.限人piu.hy.O.6l approximately 0.7%of the total (all ages)pntient base 6516d8. at this practicel. Ciwiaxda,J..Hyman,L.Hasein,M.,Everetl,D.,Norton,T. A unique clinical feature of'UMA cases identified in T,Ku,D Leske.M.C,Many.民，Mnh-Tootke,W. this present study is the slower age-related ametropc and Schciman.M.(2003)A randlumixl dinital iral of &0 04 Th Go辆tDpT
should arise in a pair of eyes that have presumably hitherto experienced the same environmental, hormonal and nutritional conditions. While it may be reasonable to postulate that a difference in the rate of emmetropisation may account for anisomyopia in an infant, this explanation is surely untenable in the context of a healthy and visually normal adolescent who first manifests UMA when (s)he enters the second decade of life. It is difficult to contemplate any exclusively unilateral influence or bias affecting agreed and accepted consensual neuro-physiological processes. Thus, for example, the possibility of any unilaterally-directed increase in parasympathetic or sympathetic activity or tone specifically at the level of the ciliary body would be most difficult to reconcile with the known facts regarding function of the autonomic nervous system (see Gilmartin, 1998). An investigation of tonic accommodation (or possibly of pupillary function) in a defined group of UMA subjects might give the lie to such suggestions. Animal studies have suggested that direct, spatiallylocal retinal-scleral communication regulates axial length of the globe. In this regard, Norton and Siegwart (1995) have speculated that if such a neural linkage is present in man, successful childhood emmetropisation must involve not only an intact and functional emmetropisation mechanism but also guaranteed exposure to a non-compromised visual environment. Again, the assumption is that any external influence will be bilateral and that any internal effect will invariably affect the neuro-physiology of both eyes. It is similarly difficult to envisage hereditary influences having anything other than a bilateral effect upon refractive development. Edwards (1998) has speculated that there might be … a genetic programming which affects the two eyes differently, or which affects the susceptibility of the two eyes to some environmental factor(s) differently. It remains to be seen whether the burgeoning genetic research directed at the decoding of the human genome throws any light on this specific developmental conundrum. However, with regard to the clinical material presented here, it must be remembered that a substantial proportion of UMA cases emerge not in infancy but in young persons entering adolescence (refer to Figure 1a). Conclusions Defining UMA as a myopic vs a plano refraction, the incidence of this specific refractive type amongst healthy and normally-sighted optometric patients aged <19 years was 2.9% [which proportion equated to approximately 0.7% of the total (all ages) patient base at this practice]. A unique clinical feature of UMA cases identified in this present study is the slower age-related ametropic progression documented in the (initially) plano eye of such individuals compared with not only the trend observed in the consistently myopic companion eye but also to that recorded in visually normal bilaterally myopic young persons. The clinical evidence discussed here implies that cases of UMA should be regarded as a subset of the myopic population, i.e. as functionally normal but distinct points on the continuum of human refractive error. Either eye, but specifically that which manifests consistent myopia, displays refractive and other characteristics typical of a visually normal developing myopic eye. This latter observation would promote the utilisation of such clinically-distinct individuals in prospective trials designed to interrupt or retard the progression of human myopia. Any treatment applied to an approximately plano eye which concurrently acted as an inherent control for its fellow myopic eye would have obvious experimental utility in trials employing either optical (bi-/multifocal spectacle lenses: Gwiazda et al., 2003), assumed-physical (rigid gas-permeable contact lenses: Walline et al., 2001) or pharmacological [e.g. Pirenzepine (a relatively selective M1-muscarinic antagonist) 2% ophthalmic gel b.i.d.: Tan et al., 2003; Siatkowski et al., 2004] therapeutic methods of inhibiting myopic progression. References Choi, S. S., Garner, L. F. and Enoch, J. M. (2003) StilesCrawford effect of the first kind (SCE-I) in post-photorefractive keratectomy and anisometropic subjects. Ophthal. Physiol. Opt. 23, 473–476. Curtin, B. J. and Karlin, D. B. (1971) Axial length measurements and fundus changes of the myopic eye. Am. J. Ophthalmol. 71, 42–53. Duke-Elder, W. S. and Abrams, D. (1970) System of Ophthalmology, Vol. V. 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