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.This is known as presbyopia, which is one of the earliest age-related lenticular changes.Theamplitude of accommodation is helpful to calculate the power of the add used in bifocal spectacles to correct presbyopia.In addition to presbyopia, ultrastructural deterioration and various biochemical changes of the crystalline lens take place with aging.The lens nucleus alsobecomes increasingly yellow with age (nuclear sclerosis), and in some cataracts the nuclear color may be brown or black.Nuclear sclerosis per se is notassociated with loss of clarity.Often it is associated with an increase in the refractive index of the lens and a myopic shift in refraction, known as lenticularmyopia.A change in color perception may result from the superimposition of a yellow filter between the retina and the incident light.III.Age-related changes.Age-related cataracts are a major cause of visual impairment in older adults.When the transparency of the crystalline lens decreasesenough to disturb vision, a clinically significant cataract exists.Such a decrease is usually the result of scattering of light rays or absorption in the axial part ofthe lens; similar changes in the peripheral parts of the lens may exist without loss of vision.Although these changes in the periphery are strictly cataractous in nature, surgical intervention is rarely warranted in the absence of visual symptoms.A cataract is characterized by the zones of the lens involved in the opacity: anterior and posterior subcapsular, anterior and posterior cortical, equatorial cortical,supranuclear, and nuclear.In certain congenital cataracts, the nuclear zone is further subdivided into adult, adolescent, infantile, fetal, and embryonic zones(Fig.7.1).There is a gradual transition but no distinct morphological differentiation between the layers of a cataract.The distinctions between these regionsrelate primarily to potential differences in their behavior and appearance during surgical procedures.A.Epidemiology of cataracts.Ninety-five percent of individuals older than 65 years of age have some degree of lens opacity; many have cataracts sufficientlydense to warrant cataract extraction.The Beaver Dam Eye Study reported that 38.8% of men and 45.9% of women older than 74 years had visuallysignificant cataracts.It is estimated that more than 1 million cataract extractions are performed each year in the United States alone.Cataract accounts formore than 15 million cases of treatable blindness in the world; extraction often leads to complete visual rehabilitation.The Baltimore Eye Survey showed thatuntreated cataract was the source of blindness in 27% of African-Americans and 13% of whites.B.Optics of cataracts.Visual disturbances resulting from a cataractous lens are secondary to fluctuation in the index of refraction creating light scatteringand/or a loss of transparency.In cortical, supranuclear, and subcapsular cataracts, protein-deficient fluid collects between fibers.The index of refraction ofthis fluid is much less than that of fiber cytoplasm, and light scattering occurs at this interface.Light scattering also occurs from large protein aggregateslinked to the cell membrane by disulfide bonds.This may cause monocular diplopia.Progressive yellowing of the lens in nuclear sclerotic cataracts causespoor hue discrimination, particularly at the blue end of the visible spectrum.The myopic shift associated with nuclear cataracts may transiently enablepresbyopic patients to read without spectacles, a condition referred to as second sight. IV.Evaluation and management of cataractsA.Symptoms of cataract formation1.Decreased vision.Cataracts cause painless progressive decrease in vision.Clinically significant cataracts cause a decrease in distance or near visualacuity.Posterior subcapsular cataracts of even mild degree can reduce visual acuity substantially.Nuclear sclerotic cataracts cause image blur atdistance but not at near.Image blur occurs when the lens loses its ability to differentiate (resolve) separate and distinct object points.When this occurs,near visual tasks, such as reading and sewing, become more difficult.Many older patients may tolerate considerable reductions in distance acuity if theirnight driving is minimal, but they may not be as tolerant of a blur that interferes with their indoor activities.2.Glare.One of the symptomatic manifestations of light scattering is glare.When a patient looks at a point source of light, the diffusion of bright white andcolored light around it drastically reduces visual acuity.The effect is akin to looking at automobile headlights at night through a dirty windshield.Posteriorsubcapsular opacification is responsible for much of the glare.3.Distortion.Cataracts may make straight edges appear wavy or curved.They may even lead to image duplication (monocular diplopia).If a patientcomplains of double vision, it is essential to determine if the diplopia is binocular or monocular.If monocular, the examiner is usually dealing with corneal,lenticular, or macular disease.4.Altered color perception.The yellowing of the lens nucleus steadily increases with age.Artists with significant nuclear sclerosis may render objectsmore brown or more yellow than they actually are.5.Unilateral cataract.A cataract may occur in only one eye or may mature more rapidly in one eye than in the other.Unless the patient is in the habit ofchecking the acuity of each eye, he or she may not be aware of the presence of a dense cataract in one eye.It is not uncommon for a patient to claim thatthe vision in the cataractous eye was lost precipitously.Because cataracts rarely mature precipitously, it is more likely that the slowly evolving lensopacity was unrecognized until the patient happened to test his or her monocular acuity.6.Behavioral changesa.Children with congenital, traumatic, or metabolic cataracts may not verbalize their visual handicap.Behavioral changes indicative of a loss of acuity orbinocular vision may alert the parents or teachers to the presence of a visual problem.Inability to see the blackboard or read with one eye may be onesuch symptom; loss of accurate depth perception, e.g., the inability to catch or hit a ball or to pour water from a pitcher into a glass, may be another.b.Prepresbyopic adults.Difficulty with night driving is frequently an early sign of cataract.c.Presbyopic adults.Frequently, maturation of nuclear cataracts is associated with the return of clear near vision as the result of increasing myopiasecondary to the higher refractive power of the rounder, harder nuclear sclerotic lens.Reading glasses or bifocals are no longer needed.This changeis called second sight. Unfortunately, the improvement in near vision is only temporary as the nuclear zone becomes more opaque.B.Signs of cataract formation1.Reduced visual acuity.Although it is not part of the usual general physical examination, the measurement of visual acuity will alert the examiner to thepresence of cataract as well as other ocular disorders.The examiner should always inquire about monocular acuity when conducting a review of systems.2.Lenticular opacification.Examination of the red reflex with the direct ophthalmoscope set on +5 (black) D at approximately 20 cm from the patientfrequently will reveal a black lens opacity against the reddish-orange hue of the reflex.This is an extremely sensitive method of detecting cataractouschange [ Pobierz całość w formacie PDF ]
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.This is known as presbyopia, which is one of the earliest age-related lenticular changes.Theamplitude of accommodation is helpful to calculate the power of the add used in bifocal spectacles to correct presbyopia.In addition to presbyopia, ultrastructural deterioration and various biochemical changes of the crystalline lens take place with aging.The lens nucleus alsobecomes increasingly yellow with age (nuclear sclerosis), and in some cataracts the nuclear color may be brown or black.Nuclear sclerosis per se is notassociated with loss of clarity.Often it is associated with an increase in the refractive index of the lens and a myopic shift in refraction, known as lenticularmyopia.A change in color perception may result from the superimposition of a yellow filter between the retina and the incident light.III.Age-related changes.Age-related cataracts are a major cause of visual impairment in older adults.When the transparency of the crystalline lens decreasesenough to disturb vision, a clinically significant cataract exists.Such a decrease is usually the result of scattering of light rays or absorption in the axial part ofthe lens; similar changes in the peripheral parts of the lens may exist without loss of vision.Although these changes in the periphery are strictly cataractous in nature, surgical intervention is rarely warranted in the absence of visual symptoms.A cataract is characterized by the zones of the lens involved in the opacity: anterior and posterior subcapsular, anterior and posterior cortical, equatorial cortical,supranuclear, and nuclear.In certain congenital cataracts, the nuclear zone is further subdivided into adult, adolescent, infantile, fetal, and embryonic zones(Fig.7.1).There is a gradual transition but no distinct morphological differentiation between the layers of a cataract.The distinctions between these regionsrelate primarily to potential differences in their behavior and appearance during surgical procedures.A.Epidemiology of cataracts.Ninety-five percent of individuals older than 65 years of age have some degree of lens opacity; many have cataracts sufficientlydense to warrant cataract extraction.The Beaver Dam Eye Study reported that 38.8% of men and 45.9% of women older than 74 years had visuallysignificant cataracts.It is estimated that more than 1 million cataract extractions are performed each year in the United States alone.Cataract accounts formore than 15 million cases of treatable blindness in the world; extraction often leads to complete visual rehabilitation.The Baltimore Eye Survey showed thatuntreated cataract was the source of blindness in 27% of African-Americans and 13% of whites.B.Optics of cataracts.Visual disturbances resulting from a cataractous lens are secondary to fluctuation in the index of refraction creating light scatteringand/or a loss of transparency.In cortical, supranuclear, and subcapsular cataracts, protein-deficient fluid collects between fibers.The index of refraction ofthis fluid is much less than that of fiber cytoplasm, and light scattering occurs at this interface.Light scattering also occurs from large protein aggregateslinked to the cell membrane by disulfide bonds.This may cause monocular diplopia.Progressive yellowing of the lens in nuclear sclerotic cataracts causespoor hue discrimination, particularly at the blue end of the visible spectrum.The myopic shift associated with nuclear cataracts may transiently enablepresbyopic patients to read without spectacles, a condition referred to as second sight. IV.Evaluation and management of cataractsA.Symptoms of cataract formation1.Decreased vision.Cataracts cause painless progressive decrease in vision.Clinically significant cataracts cause a decrease in distance or near visualacuity.Posterior subcapsular cataracts of even mild degree can reduce visual acuity substantially.Nuclear sclerotic cataracts cause image blur atdistance but not at near.Image blur occurs when the lens loses its ability to differentiate (resolve) separate and distinct object points.When this occurs,near visual tasks, such as reading and sewing, become more difficult.Many older patients may tolerate considerable reductions in distance acuity if theirnight driving is minimal, but they may not be as tolerant of a blur that interferes with their indoor activities.2.Glare.One of the symptomatic manifestations of light scattering is glare.When a patient looks at a point source of light, the diffusion of bright white andcolored light around it drastically reduces visual acuity.The effect is akin to looking at automobile headlights at night through a dirty windshield.Posteriorsubcapsular opacification is responsible for much of the glare.3.Distortion.Cataracts may make straight edges appear wavy or curved.They may even lead to image duplication (monocular diplopia).If a patientcomplains of double vision, it is essential to determine if the diplopia is binocular or monocular.If monocular, the examiner is usually dealing with corneal,lenticular, or macular disease.4.Altered color perception.The yellowing of the lens nucleus steadily increases with age.Artists with significant nuclear sclerosis may render objectsmore brown or more yellow than they actually are.5.Unilateral cataract.A cataract may occur in only one eye or may mature more rapidly in one eye than in the other.Unless the patient is in the habit ofchecking the acuity of each eye, he or she may not be aware of the presence of a dense cataract in one eye.It is not uncommon for a patient to claim thatthe vision in the cataractous eye was lost precipitously.Because cataracts rarely mature precipitously, it is more likely that the slowly evolving lensopacity was unrecognized until the patient happened to test his or her monocular acuity.6.Behavioral changesa.Children with congenital, traumatic, or metabolic cataracts may not verbalize their visual handicap.Behavioral changes indicative of a loss of acuity orbinocular vision may alert the parents or teachers to the presence of a visual problem.Inability to see the blackboard or read with one eye may be onesuch symptom; loss of accurate depth perception, e.g., the inability to catch or hit a ball or to pour water from a pitcher into a glass, may be another.b.Prepresbyopic adults.Difficulty with night driving is frequently an early sign of cataract.c.Presbyopic adults.Frequently, maturation of nuclear cataracts is associated with the return of clear near vision as the result of increasing myopiasecondary to the higher refractive power of the rounder, harder nuclear sclerotic lens.Reading glasses or bifocals are no longer needed.This changeis called second sight. Unfortunately, the improvement in near vision is only temporary as the nuclear zone becomes more opaque.B.Signs of cataract formation1.Reduced visual acuity.Although it is not part of the usual general physical examination, the measurement of visual acuity will alert the examiner to thepresence of cataract as well as other ocular disorders.The examiner should always inquire about monocular acuity when conducting a review of systems.2.Lenticular opacification.Examination of the red reflex with the direct ophthalmoscope set on +5 (black) D at approximately 20 cm from the patientfrequently will reveal a black lens opacity against the reddish-orange hue of the reflex.This is an extremely sensitive method of detecting cataractouschange [ Pobierz całość w formacie PDF ]