Refraction

Marc Laurence Adordionicio Refraction

June 18, 2009 Dr. Ferrer

Objective refraction – Measurement of the refraction of the eye that is not based on the patient's judgements, as when using an objective optometer or a retinoscope. Retinoscope - An instrument for determining objectively the refractive state of the eye. It consists of a light source, a condensing lens and a mirror. The mirror is either semitransparent or has a hole through which the retinoscopist can view the patient's eye along the retinoscope's beam of light. A patch of light is formed on the patient's retina and by moving that patch in a given direction and observing the direction in which it appears to move after refraction by the patient's eye, the retinoscopist can determine whether the patient's retina is focused in front of, at, or behind the retinoscope's sight hole. If the light reflected from the patient's fundus (called the retinoscopic reflex or light reflex) and observed in the patient's pupil through the retinoscope moves in the same direction as the movement of the mirror (this is referred to as a with movement), the eye is hyperopic. If the reflex moves in the opposite direction to that of the mirror (against movement), the eye is myopic. Sometimes it is impossible to see a clear movement one way or the other but only a bipartite reflex, showing opposite movements in the two sectors of the pupils (this is called a split reflex or a scissors movement). The refractive error is determined by placing lenses of various powers in front of the patient's eye until no movement is seen, i.e. the whole pupil is either illuminated or dark and the image of the patient's retina is then conjugate with the plane of the retinoscope's sight hole. When this phenomenon occurs the neutral point has been reached. The neutral point is measured for each principal meridian of the eye if it is astigmatic. To arrive at the patient's error of refraction the dioptric power corresponding to the distance between patient and retinoscope (called the working distance) is subtracted from the total lens power used to obtain neutralization. The amount of dioptric power subtracted is called the allowance. spot retinoscope A retinoscope that projects a circular beam of light upon the patient's retina. streak retinoscope A retinoscope that projects into the patient's eye an oblong streak, which can be adjusted in width and rotated in various meridians. It is more efficient than the spot retinoscope in determining astigmatism. Parts of retinoscope - fenestrated mirror - vergence adjusting lens - rotating line filament bulb http://medical-dictionary.thefreedictionary.com/Snell%27s+law http://medical-dictionary.thefreedictionary.com/retinoscope Optometric Instrumentation by David B. Henson

Objective Examination http://www.webmd.com/eye-health/ophthalmoscopy http://www.eyetec.net/group2/M6S1.htm http://www.stlukeseye.com/eyeq/Keratometry.asp

Ophthalmoscopy - is a test that allows a health professional to see inside the back of the eye (called the fundus) and other structures using a magnifying instrument (ophthalmoscope) and a light source. It is done as part of an eye examination and may be done as part of a routine physical examination. The fundus contains a lining of nerve cells (the retina), which detects images seen by the clear, outer covering of the eye (cornea). The fundus also contains blood vessels and the optic nerve. See a picture of the structures of the eye There are two types of ophthalmoscopy. •

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Direct ophthalmoscopy. Your health professional uses an instrument about the size of a small flashlight with several lenses that can magnify up to about 15 times. This type of ophthalmoscopy is most commonly done during a routine physical examination. Indirect ophthalmoscopy. Your health professional wears a light attached to a headband and uses a small handheld lens. Indirect ophthalmoscopy provides a wider view of the inside of the eye and allows a better view of the fundus even if the lens is clouded by cataracts.

Why It Is Done • • • •

Detect problems or diseases of the eye, such as retina problems. Help diagnose other conditions or diseases that damage the eye. Evaluate symptoms, such as headaches. Detect other problems or diseases, such as head injuries or brain tumors.

Retinoscopy - is an objective measure of the refractive error, meaning the process and results are not dependent upon patient responses. Retinoscopy is particularly valuable in situations where communication difficulties inhibit the refractometric process, such as the examination of an infant, a deaf person, a stroke victim, or someone who doesn't speak your language. Keratometry - measures the corneal curvature. It is performed for similar reasons as topography, but rather than mapping the entire corneal surface, two curves are measured – the steepest and the flattest. These measurements give the doctor information about the cornea’s curvature, focusing power, and whether astigmatism is present. Some of the uses of keratometry include calculating the intraocular lens power for cataract surgery, fitting contact lenses and monitoring the corneal curvature after surgery.

Mhay Valencia Refraction

June 18, 2009 Dr. Ferrer

Objective refraction – earliest attempt at objective evaluation of vision reported to have been made by Worth in 1929. He used five ivory balls varying in diameter from ½ inch to 1 ½ inches, which where thrown on the floor at a distance of six to seven yards from a child. The balls were spun so that they curved in their course and did not culminate in the direction expected. - since then several more precise attempts at determination have been introduced the various methods maybe separated into groups, depending on the nature of the response which can be objectively determined include: 1. oscillatory motion or pendular movement 2. optokinetic nystagmus 3. arresting nystagmus 4. galvanic skin response -

There are also objective refraction procedures, such as retinoscopy or auto refraction, in which the information is gathered without depending on responses of patient.

Clinical refraction by Borrish Book geometric, physical and visual optics

Retinoscopy – Cuigmet, in 1873, described and used retinoscopy as a method of determining the refractive state. Jackson, Duane, and others gave the technique great impetus. Copeland, more than any other individual, developed and promoted the use of “streak” retinoscopy today, retinoscopy is one of the standard and most informative tests among the refractionist`s procedures. The procedure is also known by the names of keratoscopy, shadow test, skiaskopy, keerlampsiskopie and skiametry, as well as retinoscopy. Basic principle – The retinoscope may, therefore, be either self luminous, plano or concave, spot or streak. All such factors pertain to the nature and location at the apparent source of the illumination system. Parts of retinoscope - light source - condensing lens - mirror semi transparent and it has a hole - fenestrated mirror - vergence adjusting lens - rotating line filament bulb Optometric Instrumentation by David B. Henson

Objective examination 1. slit lamp 2. retinoscope 3. ophthalmoscope