Prevalence of Ametropia PDF

Prevalence of Ametropias Dr. Ariette Acevedo, O.D. PPO2 Prevalence of Refractive Error Refractive Errors (RE) have a prevalence of ~800 million to 2.3 billion It varies with age, country, sex, ethnicity, race, occupation, environment and other. Visual environment is an important factor in eye develo...

Prevalence of Ametropias Dr. Ariette Acevedo, O.D. PPO2 Prevalence of Refractive Error Refractive Errors (RE) have a prevalence of ~800 million to 2.3 billion It varies with age, country, sex, ethnicity, race, occupation, environment and other. Visual environment is an important factor in eye development, but also there is a genetic component May be inherited from one parent, but higher probability of inheritance if both parents Genome-Wide Association Studies (GWAS) in adults have have identified 39 genetic loci associated with RE and myopia. Prevalence and incidence of myopia in adolescents Disabilities due to Refractive Error Differences in Prevalence and Progression of Myopia The Selection-Relaxation theory Poste, in 1962, evaluated the prevalence of myopia by society: Hunting and gathering: lower myopia prevalence Agriculture: some higher myopia prevalence than hunting societies Industrialized: higher prevalence of myopia Racial and Ethnic Variations Vanuatu Melanesian children: extremely low myopia prevalence Rios Negro, Amazon rainforest in Brazil Indigenous population: 1% of myopia prevalence Now: Younger Brazilian generations, higher education: higher prevalence Racial and Ethnic Variations Asian children in Taiwan, Hong King and Singapore: very high prevalence of myopia. Increases from 7% at 7 y/o to 60% at 12 y/o University students in England: 40% prevalence Medical students in Hong Kong: 95% are myopes Fact: higher myopia prevalence among medicine, law, accounting, engineering and optometry students! Optometry students have a myopia prevalence of 85% Environmental Influences In US 2-4% of children entering school have clinically significant hyperopia and astigmatism Hyperopia does not have a tendency to increase or progress during school years This indicates more hereditary factors, minimizing the environment influences. Myopia is present in 2% of children entering school in U.S. About 2% of children from ages 5-6 y/o, have -0.50DS or more of myopia Its prevalence increases markedly during school years, having a tendency to progress rapidly for a period or years. That suggest possibility of environmental influences. Myopia at birth and early childhood (related to age) Emmetropization occurs rapidly during the first year At birth there is a wide range of refractive error prevalence Eyes that are completely developed at birth tend to be emmetropic or hyperopic Eyes that do not completely develop at birth tend to be myopic By the end of the 1st year, few children are found to be myopic The myopia found in low birth weight (premature babies) is due to eye underdevelopment, not axial elongation Having steep corneas and relatively spherical, underdeveloped, lens, thus having more power Congenital vs Acquired Myopia Congenital myopia is present at birth or at a very early age, persisting through life This is not necessarily hereditary. Ex: Premature Acquired myopia Approximately 1/3 of the population in industrialized society will become myopic after several years of schooling or during adult years Factors that influence myopia development: Children with 1 myopic parent have more than 2x the risk to develop myopia Children who spend an additional hour per week outdoors significantly lowered their odds of developing myopia School Years It has long been known that children who entered school while being emmetropic become myopic during the school years Myopia tends to progress This increases in a linear form from 2% at age 6 to 20% at age 20. The Early Adult Years Myopia reaches a peak of about 30% prevalence between the ages of 20 to 40 years After 40 y/o there is a slight decrease in the percent of myopia due to the tendency of some low myopes to “loose” the myopia, rejoining the emmetropic group Myopia in the Later Adult Years Increase from 6.7% at 47-49 y/o to 15.3% beyond 75 y/o (Hirsch 1958) Hirsch attributed this to nuclear sclerosis Used a criteria of -1.13D or more of myopia US Department of Health, Education and Welfare found double the prevalence (30%), using a -0.50D or more criteria USA Age-Specific Prevalence Rates for Myopia by Age, and Race/Ethnicity UWSO and CCLR, Waterloo, Canada University of Waterloo’s School of Optometry and Vision Science study: myopia in children increases drastically from 1st grade to 8th grade 1/3 cases were undiagnosed and uncorrected History indicated that myopia used to increase by ages 12 or 13 Study: more often in kids 6 or 7 y/o (Dr. Mike Yang, Centre for Contact Lens Research (CCLR), Waterloo “Deteriorating at a much younger age” Myopia typically worsens until the age of 21 Study: an earlier onset age and may experience a much greater decline of eyesight over their lifetime compared to previous generations Projections for Myopia (2010-2030-2050) Predicted levels of myopia by 2050 Classification of Myopia Myopia classification based on observed or assumed etiological factors: Donders (1864): by prolonged close work 1. Stationary Myopia 2. Temporarily progressive myopia 3. Permanently progressive myopia Classification of Myopia Steiger (1913): based on biological variability Genetically determined Refractive error depends on the association between corneal refractive power and axial length Duke-Elder (1949): physiological vs. degenerative Physiological myopia/Simple myopia: from normal biological variability appearing between age 5 and puberty Degenerative myopia: rare, frequently leading to visual disability, even blindness Classification of Myopia Sorsby (1957): myopia and hyperopia in 2 broad categories: Plano to +/- 4.00D Greater than +/- 4.00D Most possible the axial length is beyond the range found in an emmetropic eye Goldschmidt (1968) Denmark study Low myopia is most common genetically determined, rarely exceeding 6-9D Late myopia, developing after the cessation of bodily growth and related to excessive close work High myopia excessive degrees. Causing severe reduced vision and degenerative changes Classification of Myopia Curtin (1985) classification based on the etiology, degree of myopia and time of onset 1. Physiological myopia (simple myopia) due to the correlation between the axial length and the refracting power of the eye 2. Intermediate myopia by expansion of the posterior segment of the globe (medium or moderate myopia) 3. Pathological myopia considered an ocular disease in which several complications are associated with the elongation of the eye Classification of Myopia Grosvenor (1987): Classification based on age of onset and age-related prevalence Makes no assumptions about the etiology of the various categories of myopia 1. Congenital myopia: persists throughout infancy and is present when entering school. 2% prevalence. 2. Youth-onset myopia: onset about 6 y/o through teenage years. Prevalence is 2% at age 6 to about 20% at age 20. Many are low myopes that will become emmetropes or hyperopes in later years. 3. Early Adult onset myopia: onset during the period of 20-40 y/o with a prevalence of 30%. Many will have small amounts of myopia and may become emmetropes or hyperopes later in life. 4. Late adult onset myopia: onset beyond the age of 40 with prevalence increasing in later years, major cause is nuclear cataracts. Older adults who have +2.00D gradually become myopic due to nucleus changes. Progression of Myopia Progression in children Goss and Winkler (1983) found that most cases of myopia tend to increase in a linear manner into the middle or late teen years, then levels off Found that mean age of cessation was 16 y/o for males and 15 y/o for females with a standard deviation of 2 years Progression of Myopia The earlier a child becomes myopic the more rapidly the condition tends to progress. String relationship between the progression of myopia and increase in axial length and in others also vitreous depth. Myopia Control Studies: +1.00D bifocals show to progress slowly or not at all in cases of less than 1.00D of myopia. Summer months: the increase in myopia is insignificant compared to school months periods. Atropine Multifocal SCL Orthokeratology myopia control Progression of Myopia Progression in young adults: myopia tends to progress slowly in adult years. Goss, et al. 3 categories for adult patients 1. 2. 3. Adult stabilization: rapid increase during early adolescence, then stabilization in adulthood Adult continuation: rapid increase in adolescent years, then slow progression during adult years. Adult acceleration: rate of progression accelerated after adolescence. Increase in power (steepening) of the anterior surface of the cornea is the responsible for young myopia progression. Progression of Myopia Presbyopia year: most hyperopic and emmetropic eyes undergo hyperopic shifts during presbyopic years. Small or moderate myopes will observe a decrease in myopia. Children who are highly myopic during teenage years tend to progress at a much higher rate. If it is asymmetrical, the eye with higher myopia may develop amblyopia in that eye. What causes myopia? Etiological factors: Multifactorial or polygenic: cannot be traced to a single gene or strictly environmental. Identical twins have similar refractive error Runs in family As a result of excessive near work Donders (1864): caused by prolonged tension on the eyes during close work and elongation of the axes. Sato (1957): ciliary spasm and lens- caused by accommodative spasm, followed by hypertrophy of ciliary muscle. What causes myopia? Accommodation, intraocular pressure and axial elongation Strenstroms and Sorsby determine there was an increase in axial length Proposed Prolonged near work causes an increase in IOP followed by expansion of the vitreous chamber Experiments with implanted radiosonde transducers have measured vitreous chamber pressure changes Accommodation causes a blockage of the flow of aqueous humor due to sphincter muscle pulling forward on the anterior vitreous IOP increase when fixating an object at 20cm AM: it has been found high IOP in myopic subjects in the morning Temperature: high body temperature 41C˚ to 45C˚ can cause scleral stretch (animals) What causes myopia? Von Alphen: “ciliary body and the choroid form an elastic envelope that limits the stretch of the sclera, counteracting a part of the IOP”. Macula supplies information about the focus to the brain, that feeds information to Edinger-Westphal nuclear (EWN) concerning the degree of stretch necessary to maintain emmetropia. If mechanism fail, there will be inadequate tonus of the ciliarychoroid envelope allowing the eye to stretch, causing myopia. High Myopia High myopia is defined as refractive error of at least -6.00D or an axial length ≥26.5mm. Myopic eyes are at increased risk for occurrences of ocular morbidity in later years including: Chorioretinal degeneration Retinal detachment Glaucoma Cataracts High Myopia Greene (1980): the total stress of the posterior sclera caused by IOP and oblique muscles, accounts for posterior staphyloma. Corneal radius is also involved in myopia. In myopes older than 18 with myopia progression, there is also corneal steepening. Pathologic or degenerative myopia Definition: “high myopia with any posterior myopia-specific pathology from axial elongation” Progressive and irreversible Affects ~3% of the world population Global prevalence is from 0.9- 3.1% with regional variability Prevalence of pathologic myopia- related visual impairment is: From 0.1% to 0.5% in European studies From 0.2% to 1.4% in Asian studies Pathologic Myopia Etiology: Biomechanical forces related to axial elongation resulting in stretching of the ocular layers and progressive thinning of the retina, choroid and sclera. Risk factors: Primary risk factor: greater axial length and age. Additional risk factors: Female gender Larger optic disc area FOH of myopia Pathologic changes in myopic eyes Indicators of a posterior staphyloma Optic nerve crescents Myopic cupping (ONH) Peripapillary detachment Disruption of the retinal pigment epithelium Pathological changes in myopic eyes Chorioretinal degeneration Retinal detachment Glaucoma Cataracts Ocular and systemic disease in highly myopic children Anomalous Myopias In these the accommodation stimulus is insufficient for the patient’s accommodative response Night myopia: presents in low visibility conditions due to the fact that there is not an adequate stimulus to accommodation. Pupil dilation leads to spherical aberration Empty field myopia: in photopic conditions in which there is not sufficient detail in the central visual field to provide stimulus of accommodation Pilots Instrument myopia: accommodation is stimulated by instrument and response is not appropriate. Microscopes Hyperopia Hyperopia Hyperopia prevalence during school years is 6% from age 6 to 15. Many can accommodate and overcome the low hyperopia until their amplitude of accommodation is lower and cannot compensate anymore. Usually goes undetected in screening tests. Hyperopia Manifest hyperopia: facultative and absolute Facultative: portion of the hyperopia that can be overcome (compensated) with accommodation. Absolute: part of the hyperopia that cannot be compensated with accommodation. Latent hyperopia: hypermetropia that reveals only under cycloplegia. Example: 5 y/o HF Objective Refraction: +3.00DS OD and OS Subjective Refraction: +2.00DS OD and OS VA 20/20 Cycloplegic Refraction: +5.00DS OD and OS Hyperopia When excessive amounts of accommodation must be constantly used in order to obtain clear vision, there is excessive accommodative convergence, resulting in crossed eyes, esotropia. Even if esotropia does not occur, the eyestrain of prolonged near work in uncorrected hyperopia results in serious problems in children’s ability to read. Hyperopia When excessive amount of accommodation is required to compensate an uncorrected hyperopia, the visual system has 3 choices: 1. Let the letters be out of focus, impossible to read. 2. One eye turns inward, reliving the eyestrain but causing double vision (diplopia). 3. Overconvergence: single vision (SV) is maintained but with large amount of stress due to unconscious continuous overconvergence, avoiding double vision. Indications for Cycloplegic Refraction Children with constant or intermittent ET on 1st visit Accommodative esotropias (eye inward) Suspected or having latent hyperopia Suspected pseudo-myopia Uncooperative/non-communicative patients Variable/inconsistent endpoints in subjective refraction Children and young adults with asthenopia Children and young patient with esophoria, accommodative insufficiency , accommodative fatigue, accommodative inertia, spasm of accommodation All children younger than 3 y/o Hyperopia During the first 6 months of life an eye turns inward After that it is most likely to happen due to high hyperopia or less common, paralysis of extraocular muscle or nerve. In this case if not corrected the eye will suppress and become amblyopic. Hyperopia Progression Hyperopics in early adulthood tend to become more hyperopic and also the emmetropic patient, but the changes are very slow with the years. Age related hyperopia can be due to gradual decrease in the refractive error of the crystalline lens or maybe small decrease in the axial length. Uncorrected hyperopia and reading problems Uncorrected hyperopic children have problems adjusting to school Slow readers Worst in performing visual perception skill tests Unfortunately school and pediatrician’s screenings are directed toward myopes Better vision screenings are needed Hyperopia can usually be detected by clinical refraction, thus most of the time there is no VA complaint How to detect possible hyperopes During screening, while taking VA at distance, if the child was able to read the 20/20 line: Introduce a trial lens of +1.00D and ask the child to read again the 20/20 line If they cannot read it with +1.00D: passed screening If they can read it with +1.00D: failed screening It is very possible that they are hyperopes (can read the letters without the lens because they use accommodation to compensate for uncorrected hyperopia) Hyperopia Several states are making it a law to have a comprehensive eye examination before preschool InfantSEE program from AOA for babies Also as eyecare professionals we need to be aware of when to prescribe Study by Atkinson, determined if +3.50 or more is not corrected, they are at risk of developing strabismus or amblyopia. The correction will not alter the emmetropization of the eye Critical when to prescribe Astigmatism Astigmatism Types of astigmatism: A. B. C. D. E. Compound myopic Simple myopic Mixed Simple hyperopic Compound hyperopic Astigmatism Children tend to have WTR astigmatism According to a USA study 28.4% of children between the ages of 5 and 17 have astigmatism Kleinstein, R.N.; Jones, LA; Hullett, S et al. (2003) “Refractive Error and Ethnicity in Children”. Archives of Ophthalmology 121 (8): 1141-7 Elderly tend to have ATR astigmatism Astigmatism According to different studies: Northeastern Brazil: 34% of the students were astigmatic Garcia, Carlos Alexandre de Amorim; Oréfice, Fernando; Nobre, Gabrielle Fernandes Dutra; Souza, Dilenede Brito; Rocha, Marta Liliane Ramalho; Vianna, Raul Navarro Garrido (2005). "Prevalence of refractive errors in students in Northeastern Brazil". ArquivosBrasileirosde Oftalmologia68(3): 321–5. Bangladesh: 32.4% of adults older than 30 y/o had astigmatism Bourne, R; Dineen, BP; Ali, SM; NoorulHuq, DM; Johnson, GJ (2004). "Prevalence of refractive error in Bangladeshi adults*1Results of the National Blindness and Low Vision Survey of Bangladesh". Ophthalmology111(6): 1150–60