CLINICAL APPROACH TO REFRACTIVE ERRORS Ayesha Abdullah 27.11.2017 .11.2017

Learning objectives By the end of this lecture the students would be able to Correlate optics with the underlying problem in various types of refractive errors & their correction with lenses Describe the clinical presentation of refractive errors Outline the clinical protocol for the assessment of refractive errors

To begin with Light ? Refraction ? Main refractive surface of the eye? Why is it so? How much is the refractive power of the cornea? Refractive errors? How much is the role of lens in refraction? What is the role of accommodation in refraction? How much is the refractive power of the cornea? 40-44 diopters During accommodation in a youthful eye the lens can change its refractive power from 19 D to 33 D

What is Emmetropia & Ametropia? The state of having no refractive error is emmetropia A Balanced state of refractive power of the cornea, lens and the length of the eyeball Parallel rays of light are brought to a focus on the fovea when the eye is not accommodating The state of the eye when parallel rays of light are not focused on the fovea with the accommodation relaxed is called ametropia The state of having no refractive error is emmetropia ; a balanced state of refractive power of the cornea, lens and the length of the eyeball. Parallel rays of light are brought to a focus on the fovea when the eye is not accommodating The state of the eye when the refractive power of the cornea, lens and the length of the eye do not correlate and as a result the parallel rays of light are not focused on the fovea is called ametropia

What determines the type and amount of refractive error? For all newborns, the refractive state is mostly hyperopic accompanied by some degree of astigmatism. Along with the development of the eyes, the degree of both hyperopia and astigmatism decreases gradually, and the refractive state of the eye develops to emmetropia via the process of “process of emmetropization”. In this process, the corresponding changes of the refractive components (cornea and/or lens) of the eye maintain the eye in an ‘emmetropia’ state. But with the increase of refraction and ocular AL, the corneal compensation decreases gradually and its emmetropization ability becomes limited in a certain range. Int J Clin Exp Med 2015;8(8):13639-13643

What determines the type and amount of refractive error? An interplay among corneal power, lens power, anterior chamber depth, axial length Determines an individual’s refractive status CAAL An interplay among corneal power, lens power, anterior chamber depth, and axial length determines an individual’s refractive status. All 4 elements change continuously as the eye grows. On average, babies are born with about 3.00 D of hyperopia. In the first few months of life, this hyperopia may increase slightly, but it then declines to an average of about 1.00 D of hyperopia by the end of the first year because of marked changes in corneal and lenticular powers, as well as axial length growth. By the end of the second year, the anterior segment attains adult proportions; however, the curvatures of the refracting surfaces continue to change measurably. One study found that average corneal power decreased 0.10–0.20 D and lens power decreased about 1.80 D between ages 3 years and 14 years. From birth to age 6 years, the axial length of the eye grows by approximately 5 mm; thus, one might expect a high prevalence of myopia in infants. However, most children’s eyes are actually emmetropic, with only a 2% incidence of myopia at 6 years. This phenomenon is due to a stillundetermined mechanism called emmetropization. During this period of eye growth, a compensatory loss of 4.00 D of corneal power and 2.00 D of lens power keeps most eyes close to emmetropia. It appears that the immature human eye develops so as to reduce refractive errors.

Emmetropia Axial length matches dioptric power of the eye & parallel rays of light are brought to a focus onto the retina The average newborn’s eyeball is about 16 millimeters in diameter, from front to back (axial length). In an infant, the eye grows slightly to a length of approximately 19½ millimeters. The eye continues to grow, gradually, to the length of about 24-25 millimeters. The Axial Length (AL) is the distance from the corneal surface to an interference peak corresponding to the retinal pigment epithelium/Bruch’s membranee . A majority of axial length elongation takes place in the first 3 to 6 months of life and a gradual reduction of growth over the next two years, J Clin Diagn Res. 2013 Oct; 7(10): 2211–2212. The far point of the emmetropic eye is at infinity, and infinity is conjugate with the retina

What determines the type and amount of refractive error? Refractive errors of up to 5 D are considered to be biological variation Higher degrees of refractive errors can be associated with structural anomalies of the ocular structures e.g. the cornea, lens, choroid and the retina (1m.m. change in AL represents about 3 dioptres change in refraction)

CIA Ametropia Axial Curvature Index When parallel rays of light are NOT brought to a focus onto the retina Ametropia could be Axial Curvature Index CIA Axial (1m.m. change= 3 dioptres change in refraction) Curvature (1m.m. change in radius of curvature of cornea represents= 6 dioptres of change in refraction. ) Index ; due to change in the refractive index of the refractive media From birth to the adulthood, the length of the ocular eye axis increases about 8 millimeter and in case that there are no corresponding adjustments of other factors to adapt to the growth of the eye axis, the misbalance can result in up to 20.0 diopter (D) myopias During the development of the eyes, along with the growing ocular AL, the crystalline lens and cornea curvatures (CRs) gradually become flat in order to reduce the refractive power accordingly and to contradict the increased axial refraction changes to a certain degree, finally reducing myopia severity. Although the corneal refractive power mediates about three-fourths of the total eye refraction power, a number of clinical studies have shown that the ocular AL is also an important factor, which significantly influences the refractive state. Differences of ocular ALs growth rates between both eyes have been proposed to be the main cause for anisometropia in children  Int J Clin Exp Med 2015;8(8):13639-13643

Types of Ametropia Myopia, common in young age group Hyperopia, common in very young children & old age Astigmatism; common in young age group but less common than myopia Myopia: From Greek myops- squinting myein-to close

Myopia Parallel rays brought to a focus in front of the retina. The eye has more refractive power than required for the axial length of the eye

Simple Myopia Usual onset by adolescence but may begin as late as 25 years of age. Gradually increases until the eye is fully grown Seldom exceeds -6 dioptres.

Pathological myopia Commonly begins as physiological but rather than stabilizing when adult size of the eyeball is achieved, the eye continues to enlarge. It is associated with pathological changes in the posterior segment that can be seen on Ophthalmoscopy It can lead to complications like retinal breaks and detachment Can go upto over -20 diopters Commonly begins as physiological but rather than stabilizing when adult size of the eyeball is achieved, the eye continues to enlarge. It is associated with pathological changes in the posterior segment that can be seen on ophthalmoscopy It can lead to complications like retinal breaks and detachment Can go upto over -20 diopters

Hyperopia/ Hypermetropia Parallel rays brought to a focus BEHIND the retina. The eye has less refractive power than required for the axial length of the eye.

Hyperopia Manifest Latent or Hidden At birth practically all eyes are hypermetropic to the extent of +2.5 to +3.0 diopters. Emmetropisation occurs as the eye grows. Emmetropia may not be reached and hypermetropia may persist. – to measure this the accommodation has to be knocked off through cycloplegic agents like cyclopentolate and atropine

Astigmatism The eye has different refractive power in different meridians of the eye e.g Vertical rays being focused in one position (in front, behind or on the fovea) and horizontal rays focused on another Myopia, hypermteropic or mixed astigmatism When the two meridians are at right angle to each other its called regular astigmatism otherwise its termed as irregular astigmatism

Regular if the principal meridia are at right angle to each other and irregular if they are not

How do refractive errors present? Asthenopia , eyestrain & visual fatigue Blurring of vision Ocular discomfort with itching, burning of the eyes and at times increased sensitivity to light etc Headache Headache presenting after visual work especially in those above 40 years could be because of RE, however a headache presenting early morning is extremely unlikely to be because of RE

http://www.richmondeye.com/simulations-of-eye-disorders/

In Pre-school children Can present in a variety of ways In preverbal children it can present as delayed milestones of visual development; inability to focus at visually stimulating objects, follow light or bright object Squint Lazy eye or eyes

In school going children Lack of interest in visual tasks, class work Generally apathic or withdrawn behaviour Difficulty in reading or seeing the black/ white board from distance Squint Lazy eye

Signs Decreased visual acuity that improves with pinhole The eyeball may be obviously small (hyperopia) or large (myopia) The cornea my be conical in shape (irregular astigmatism (keratoconus) Pupils are normal Posterior segment may show abnormalities

Normal fundus

psedudopapiloedma

Treatment of RE Spectacles Contact lens Refractive surgery

Refractive assessment – Retinoscopy Retinoscope Ophthalmoscope

Retinoscopy/ manual refraction

Autorefraction

Presbyopia What is Presbyopia? Physiological failure of the lens to accommodation due to hardening of lens with age weakness of ciliary’s muscle and suspensory ligament How is it corrected? Suitable spherical lens for near work A plus lens or a lesser minus lens

Which of the following types of refractive error varies in different meridia Myopia Hyperopia Astigamtism Presbyopia

Which of the following is the least invasive procedure for the correction or refractive errors Spectacles Contact lenses Laser refractive surgery Reractive surgery Clear lens extraction

Which of the following is most useful in the diagnosis of refractive error Assessment of distance VA Assessment of Near VA Assessment of Pupils Assessment of pinhole VA Ophthalmoscopy