Optical Techniques Dept. - Refractive Errors - 2023-2024 - Sawa University - PDF

‫ﺑﺴﻢ ﺍﻟﻠﻪ ﺍﻟﺮﺣﻤﻦ ﺍﻟﺮﺣﻴﻢ‬  Republic of Iraq The ministry of higher education and scientific research Sawa University Optical techniques Depts. Educational lessons in Optical techniques Dept.. – Refractive errors 2023-2024...

‫ﺑﺴﻢ ﺍﻟﻠﻪ ﺍﻟﺮﺣﻤﻦ ﺍﻟﺮﺣﻴﻢ‬  Republic of Iraq The ministry of higher education and scientific research Sawa University Optical techniques Depts. Educational lessons in Optical techniques Dept.. – Refractive errors 2023-2024 Directed by instructor:Attallah B.Hmood Optical techniques Dept. Sawa University  First lecture 1.Introduction Second Stage :Optical techniques Dept.  Overview Target Group:second Stage of Optical Dept. im of This Lecture is Familiarity of Refractive The A Errors In the end of this lecture ,the students will know what do we mean by refractive errors A.(1) defintion. Normal vision When a person have 20/20 vision or 6/6 vision , he can see an object that is (20 feet ) or 6 meters away clearly. The term refers to average, normal vision. If his vision doesn’t measure 20/20 or 6/6 , he may need to wear contact lenses or glasses to see clearly. Visual acuity (VA) Visual acuity (VA) is a measure of the ability of the eye to distinguish shapes and the details of objects at a given distance. It is important to assess VA in a consistent way in order to detect any changes in vision SAWA UNIVERSITY Optical Department College of Health and Medical Technology By instructor ATTALLAH B.HMOOD Visual Acuity Visual acuity is the ability to see distinct figures and fine detail with clarity. With good visual acuity, the outline of an object is sharp and easily detectable We can also say that the visual acuity is a measure of the spatial resolution of the eye or, in other words, an estimation of its ability to distinguish between two points. Visual acuity refers to your ability to discern the shapes and details of the things you see. It’s just one factor in your overall vision. Others include color vision, peripheral vision, and depth perception. PRISMS AND LENSES  PRISM: One of the most common uses for an eye doctor prescribing prisms is to treat a condition known as Binocular Visual Dysfunction (BVD). Prisms, by definition, are triangular in shape, and made of plastic or glass for the purpose of dispersing light into a spectrum, or changing the direction in which light is reflected. ‫ﺃﺣﺪ ﺍﻻﺳﺘﺨﺪﺍﻣﺎﺕ ﺍﻷﻛﺜﺮ ﺷﻴﻮًﻋﺎ ﺍﻟﺘﻲ ﻳﺼﻔﻬﺎ ﻃﺒﻴﺐ ﺍﻟﻌﻴﻮﻥ ﻟﻠﻤﻨﺸﻮﺭ ﻫﻮ ﻋﻼﺝ ﺣﺎﻟﺔ ﺗﻌﺮﻑ ﺑﺎﺳﻢ ﺍﻟﺨﻠﻞ‬ ‫ ﻭﻣﺼﻨﻮﻉ ﻣﻦ‬،‫ ﻫﻮ ﻣﺜﻠﺚ ﺍﻟﺸﻜﻞ‬،‫ ﺑﺤﻜﻢ ﺗﻌﺮﻳﻔﻪ‬،‫(ﺍﻟﻤﻮﺷﻮﺭ‬BVD). ‫ﺍﻟﻮﻇﻴﻔﻲ ﺍﻟﺒﺼﺮﻱ ﺛﻨﺎﺋﻲ ﺍﻟﻌﻴﻨﻴﻦ‬.‫ ﺃﻭ ﺗﻐﻴﻴﺮ ﺍﻻﺗﺠﺎﻩ ﺍﻟﺬﻱ ﻳﻨﻌﻜﺲ ﻓﻴﻪ ﺍﻟﻀﻮﺀ‬،‫ﺍﻟﺒﻼﺳﺘﻴﻚ ﺃﻭ ﺍﻟﺰﺟﺎﺝ ﻟﻐﺮﺽ ﺗﺸﺘﻴﺖ ﺍﻟﻀﻮﺀ ﺇﻟﻰ ﻃﻴﻒ‬ A transparent body that bounded in part by two nonparallel plane faces ‫ﺟﺴﻢ ﺷﻔﺎﻑ ﻳﺤﺪﻩ ﺟﺰﺋﻴﺎ ﻭﺟﻬﺎﻥ ﻣﺴﺘﻮﻳﺎﻥ ﻏﻴﺮ ﻣﺘﻮﺍﺯﻳﻴﻦ‬ ‫ﺍﻟﻌﺪﺳﺔ ﻋﺒﺎﺭﺓ ﻋﻦ ﺟﻬﺎﺯ ﺑﺼﺮﻱ ﻧﺎﻗﻞ ﻳﺮﻛﺰ ﺃﻭ ﻳﺸﺘﺖ ﺷﻌﺎﻉ ﺍﻟﻀﻮﺀ ﻋﻦ ﻃﺮﻳﻖ ﺍﻻﻧﻜﺴﺎﺭ‬ A portion of a refracting media bordered by two surfaces. LENSES TYPES  Refractve errors Refractive error is an optical defect in which rays of light from optical infinity fail to converge on the fovea in the non-accommodating eye. Cornea and lens, the main ocular refractive elements, form a relative thick lens refracting complex that operates as functional syncytium. The outcome of cornea-lens interactions on incident beam of light are refracted rays destined for the fovea. However, not all refracted rays will reach the fovea, some fall short while others exceed it.in other words, the refractive rays don’t fell in the same phase. The types of refractive errors The most common types of refractive errors are myopia, hyperopia, presbyopia, and astigmatism. (1) Myopia (nearsightedness) or(shortsightedness), the word of myopia belong to GREEG origin , means “closs the eye”. myopia is a condition where objects up close appear clearly, while objects far away appear blurry. With myopia, light comes to focus in front of the retina instead of on the retina. Besides, myopia occurs when the eye is too long, when the cornea is more curved than normal or when crystalline lens has too much dioptric power. These changes cause distant objects to be focused in front of the retina instead of on the retina. This makes distant objects looks blurry but close-up objects look clear. Fig. (1) myopia type  *Correction vision In order to correct eye vision ,the object image must be occur at the retina. Hence We have to put a concave lens in front of eye.the falling light will scatter in a specific refraction angle, that makes the falling light focuses on retina ‫ ﻳﺠﺐ ﺃﻥ‬، ‫ﻣﻦ ﺃﺟﻞ ﺗﺼﺤﻴﺢ ﺭﺅﻴﺔ ﺍﻟﻌﻴﻦ‬.‫ﺗﻈﻬﺮ ﺻﻮﺭﺓ ﺍﻟﺠﺴﻢ ﻋﻠﻰ ﺷﺒﻜﻴﺔ ﺍﻟﻌﻴﻦ‬ ‫ﺑﺎﻟﺘﺎﻟﻲ‬ ، ‫ﻳﺠﺐ ﺃﻥ ﻧﻀﻊ ﻋﺪﺳﺔ ﻣﻘﻌﺮﺓ ﺃﻣﺎﻡ ﺍﻟﻌﻴﻦ‬ ‫ﻓﺎﻟﻀﻮﺀ ﺍﻟﺴﺎﻗﻂ ﺳﻮﻑ ﻳﺘﺸﺘﺖ ﻓﻲ‬ ‫ ﺗﺠﻌﻞ ﺍﻟﻀﻮﺀ‬، ‫ﺯﺍﻭﻳﺔ ﺍﻻﻧﻜﺴﺎﺭ ﻣﻌﻴﻨﺔ‬ ‫ﺍﻟﺴﺎﻗﻂ ﻳﺮﻛﺰ ﻋﻠﻰ ﺷﺒﻜﻴﺔ ﺍﻟﻌﻴﻦ‬ Fig.(2) (a)normal vision—(b) myopia—( c) correction with concave lens  (2) Hyperopia (farsightedness) is a common type of refractive error where distant objects may be seen more clearly than objects that are near. However, people experience hyperopia differently. Some people may not notice any problems with their vision, especially when they are young. For people with significant hyperopia, vision can be blurry for objects at any distance, near or far. Hyperopia, on the other hand, also produces an inability to correctly focus images on the retina. However, unlike myopic people, hyperopic people have blurred vision up close, since the eye is shorter and focuses nearby objects behind the retina We cannot have myopia and hyperopia in the same eye.But you can find in the same patient the hyperopia in one eye and myopia in another, while this is rarely occured...  (3) Astigmatism is a condition in which the eye does not focus light evenly onto the retina, the light-sensitive tissue at the back of the eye. This can cause images to appear blurry and stretched out. (4) Presbyopia is an age-related condition in which the ability to focus up close becomes more difficult. As the eye ages, the lens can no longer change shape enough to allow the eye to focus close objects clearly  The major reasons of Reactive errors (a.) Abnormality in the size of the eyeball – The length of the eyeball is too long in myopia and too short in hypermetropia. (b.) Abnormality in the curvature of the cornea – The curvature of the cornea is too steep in myopia and too flat in hypermetropia. In addition, irregularity of the corneal surface may give rise to astigmatism. (c. )Abnormality in the refractive index – Light passes through the major refracting surfaces like the cornea and lens, before impinging on the retina. A high refractive index may cause myopia, while a low refractive index may cause hypermetropia. In all these factors, the abnormality of the size of the eyeball is most common in producing refractive errors  VISUAL ANGLE VISUAL ANGLE is the angle subtended at nodal point of eye by an object in visual field. As shown in [ Fig. 3 ] is the angle a viewed object subtends at the eye, usually stated in degrees of arc. It also is called the object's angular size.  ‫))‪(Fig : (3‬‬ ‫‪V‬‬ ‫ﺗﻜﻮﻥ ﻓﺠﻮﺓ )‪(d‬‬  Visual Acuity Test A visual acuity test is an eye exam that checks how well you see the details of a letter or symbol from a specific distance. There are several different types of visual acuity tests, most of which are very simple. Depending on the type of test and where it’s conducted, the exam can be performed by:  Visual Acuity Test an optometrist ‫ﻃﺒﻴﺐ ﻋﻴﻮﻥ‬ an ophthalmologist ‫ﺍﺧﺼﺎﺋﻲ ﺑﺼﺮﻳﺎﺕ‬ an optician ‫ﺍﺧﺼﺎﺋﻲ ﻧﻈﺎﺭﺍﺕ‬ a technician ‫ﻓﻨﻲ ﺑﺼﺮﻳﺎﺕ‬ a nurse ‫ﻣﻤﺮﺽ ﺍﺧﺘﺼﺎﺹ‬ The Aim Of Tests We are usually need an eye exam. if we feel that we’re experiencing a vision problem or our vision has changed. A visual acuity test is one part of a comprehensive eye exam, that we have to do in periodic times.  The visual acuity tests are useful for the following An infant or child has proper visual development A person has the required visual acuity to get a drivers lecence. A person qualifies for special services or for new appointment A disease has progressed and caused changes in vision. For stabilizing vision or preventing vision loss. visual acuity test Performance of Performance of visual acuity tests are fulfilled by several different types of visual acuity tests:- (1) Snellen The Snellen test uses a chart of letters or symbols. You’ve probably seen the chart in a school nurse’s office or eye doctor’s office. The letters are different sizes and arranged in rows and columns. As in Fig.(4) from 14 to 20 feet away, this chart helps determine how well you can see letters and shapes. Fig. (4) Snellen chart.  (2) Random E In the random E test, we’ll identify the direction the letter “E”. A patient will point in the direction the letter is facing: up, down, left, or right. As in shown in fig. (5)  The distance from patient To the chart The distance from normal person can read the letter in the chart (3) Simple picture chart picture chart is used for test visual acuity in 2 to 4 years of infant and e children as well as For patient is about to be blind Fig.(6) Simple picture chart  (4) LANDOLT’S ChART TEST Landolt C is used for testing illiterate patients that are not familiar with specific alphabet.Or it used for non-English speakers. Landolt C vision test are considered one of the best among alternative visual acuity tests. As shown in Fig.(4) below.A circle with a break in it, shown in Fig (4) (a), ‫ ﺗﺴﺘﺨﺪﻡ ﻃﺮﻳﻘﺔ ﻻﻧﺪﻭﻟﺖ ﻻﺧﺘﺒﺎﺭ ﺍﻟﻤﺮﺿﻰ ﺍﻻﻣﻴﻴﻦ ﺍﻟﺬﻳﻦ ﻟﻴﺴﻮﺍ ﻋﻠﻰ ﺩﺭﺍﻳﺔ‬ ‫ﺑﺎﺑﺠﺪﻳﺎﺕ ﺍﻟﻠﻐﺎﺕ ﺍﻟﻤﻌﻴﻴﻨﻪ ﺍﻟﻤﺴﺘﺨﺪﻣﺔ ﺑﻄﺮﻕ ﺍﻟﻔﺤﺺ ﻭﺗﻌﺘﺒﺮ ﻫﺬﻩ ﺍﻟﻄﺮﻳﻘﺔ ﺍﻓﻀﻞ‬ ‫ﺍﻻﺧﺘﺒﺎﺭﺍﺕ ﺍﻟﺒﺪﻳﻠﺔ ﻟﻘﻴﺎﺱ ﺣﺪﺓ ﺍﻟﺒﺼﺮ‬ The break or gap is 1 stroke width wide. While the entire diameter of the ring is 3 times of the stroke width of the circle. And the external diameter of the circle is 5 times of stroke width. Fig.(7) Landolt C Chart (a) (c) (b)  (5) - LogMAR chart Logarithm of the Minimum Angle of Resolution is a chart consisting of rows of letters that is used by optometrists. As shown in Fig. (8) The MAR is arrived at by dividing the denominator by the distance at which the Letters were read , in other words, the Snellen fraction is inverted and reduced. A Snellen acuity of 6/12 or 20/40 therefore Fig.(8) Corresponds to a MAR of 2.  The derivation has been used in the construction of chart such as the Bailey- Lovie chart. Fig (9)comparing table between Acuity Snellen and LogMAR Standard visual acuity scales Fig (10)  ‫‪PROCEDUREFOR RECORDING VISUAL ACUITY :‬‬ ‫ﺇﺟﺮﺍﺀ ﺗﺴﺠﻴﻞ ﺣﺪﺓ ﺍﻟﺒﺼﺮ‬ ‫ ‬ ‫‪ Patient seated at 6m distant from the chart exerts‬‬ ‫ﻳﺠﻠﺲ ﺍﻟﻤﺮﻳﺾ ﻋﻠﻰ ﺑﻌﺪ ‪ 6‬ﺃﻣﺘﺎﺭ ﻣﻦ ﺍﻟﺮﺳﻢ ﺍﻟﺒﻴﺎﻧﻲ‬ ‫ ‬ ‫‪minimal accommodation‬‬ ‫ﻳﺠﺮﻱ ﺍﺧﺘﺎﺑﺎﺭﻩ ﻋﻨﺪ ﺍﻟﺤﺪ ﺍﻷﺩﻧﻰ ﻣﻦ ﺍﻹﻗﺎﻣﺔ‬ ‫ ‬ ‫‪ Chart should be properly illuminated‬‬ ‫ﻳﺠﺐ ﺃﻥ ﻳﻜﻮﻥ ﺍﻟﻤﺨﻄﻂ ﻣﻀﺎﺀ ﺑﺸﻜﻞ ﺻﺤﻴﺢ‬ ‫ ‬ ‫‪ The pt is asked to read the chart with each eye‬‬ ‫ُﻳﻄﻠﺐ ﻣﻦ ﺍﻟﻤﺮﻳﺾ ﻗﺮﺍﺀﺓ ﺍﻟﺮﺳﻢ ﺍﻟﺒﻴﺎﻧﻲ ﻟﻜﻞ ﻋﻴﻦ ﻋﻠﻰ ﺣﺪﺓ ﻭﻳﺘﻢ ‪,‬‬ ‫ ‬ ‫‪separately and VA is recorded‬‬ ‫ﻭﺗﺴﺠﻞ ﺣﺪﺓ ﺍﻟﺒﺼﺮ ﺍﻟﻤﻄﻠﻮﺑﺔ ﻣﻦ ﻗﺒﻞ ﺍﻟﻤﺨﺘﺺ ﺑﺎﻟﺒﺼﺮﻳﺎﺕ‬ ‫ ‬ ‫ﻣﻌﺘﻤﺪﺍ ﻋﻠﻰ ﺍﺻﻐﺮ ﻣﺴﺎﻓﺔ ﻋﻦ ﺧﻂ ﺍﻟﺤﺮﻭﻑ ﺍﻟﺘﻲ ﺑﺎﻣﻜﺎﻥ ﺍﻟﻤﺮﻳﺾ ﺭﺅﻴﺘﻬﺎ‪ Depending upon the smallest line that the pt can‬‬ ‫ ‬ ‫ﻣﻦ ﻣﺴﺎﻓﺔ ‪ 6‬ﻣﺘﺮ ﻓﺘﻜﻮﻥ ﺣﺪﺓ ﺑﺼﺮﻩ \ ﺑﺼﺮﻫﺎ ﻣﺜﻼ ‪read from 6m distance, his/her VA is as 6/6, 6/9,24\6 , 18\6 ,,12\6, ,9\6 6\6‬‬ ‫‪ 36\6 ,‬ﻭ ‪60\6‬‬ ‫ ‬ ‫‪6/12, 6/18, 6/24, 6/36 and 6/60‬‬ ‫ ‬ ‫ﺇﺫﺍ ﻟﻢ ﻳﺘﻤﻜﻦ ﺍﻟﻤﺮﻳﺾ ﻣﻦ ﺭﺅﻴﺔ ﺍﻟﺨﻂ ﺍﻟﻌﻠﻮﻱ ﻣﻦ ‪ 6‬ﺃﻣﺘﺎﺭ ‪ If one cannot see the top line from 6m, pt is asked،‬‬ ‫ ‬ ‫ﻳﻄﻠﺐ ﻣﻦ ﺍﻟﻤﺮﻳﺾ ﺍﻟﺴﻴﺮ ﺑﺒﻄﺀ ﺣﺘﻰ ﻳﺘﻤﻜﻦ ﻣﻦ ﻗﺮﺍﺀﺓ ﺍﻟﺴﻄﺮ ﺍﻟﻌﻠﻮﻱ ﻣﻦ ﺍﻟﺤﺮﻭﻑ‪to slowly walk towards the chart till can read the‬‬ ‫ ‬ ‫‪top line‬‬ ‫ ‬ ‫ﺍﻻﻋﺘﻤﺎﺩ ﻋﻠﻰ ﺍﻟﻤﺴﺎﻓﺔ ﺍﻟﺘﻲ ﻳﻤﻜﻦ ﺍﻟﻤﺮﻳﺾ ﺭﺅﻴﺔ ﺍﻟﺴﻄﺮ ﺍﻟﻌﻠﻮﻱ ﻣﻦ ﺍﻟﺤﺮﻭﻑ‪ Depending upon the distance at which one can read‬‬ ‫ ‬ ‫ﻋﻨﺪﻫﺎ ﺗﺴﺠﻞ ﺣﺪﺓ ﺍﻟﺒﺼﺮ ﻣﺜﻼ ‪ 60\60,1\60,2\3 ,60\60,4\60,5\5‬ﻭﻫﻜﺬﺍ ‪the top line, the vision is recorded as 5/60, 4/60,‬‬ ‫ ‬ ‫‪3/60, 2/60, 1/60‬‬ ‫‪:‬‬ ‫ ‬  If the patient is unable to read the top line even from 1m,. ‫ ﺇﺫﺍ ﻛﺎﻥ ﺍﻟﻤﺮﻳﺾ ﻏﻴﺮ ﻗﺎﺩﺭ ﻋﻠﻰ ﻗﺮﺍﺀﺓ ﺍﻟﺴﻄﺮﺍﻟﻌﻠﻮﻱ ﺣﺘﻰ ﻣﻦ ﻣﺘﺮ ﻭﺍﺣﺪ‬ he/she is asked to Count fingers (CF) of the examiner ‫ﻳﺴﺄﻝ ﺍﻟﻤﺮﻳﺾ ﺍﻭ ﺍﻟﻤﺮﻳﻀﺔ ﻟﻌﺪ ﺍﻻﺻﺎﺑﻊ ﻟﻴﺮ ﺍﻟﻔﺎﺣﺺ‬ His/her VA is recorded as CF-3’, CF-2’, CF-1’ or CF close to face depending upon the distance at which the pt is able to count fingers. ‫ﺃﻭ‬CF- 1 ‫ﺃﻭ‬CF-2 ‫ﺃﻭ‬CF-3 ‫ ( ﺍﻟﺨﺎﺹ ﺑﻪ ﻋﻠﻰ ﺃﻧﻪ‬VA)‫ ﺗﺴﺠﻴﻞ ﺟﻬﺎﺯ ﺣﺪﺓ ﺍﻟﺒﺼﺮ‬ ‫ﻕﺮﻳﺐ ﻣﻦ ﺍﻟﻮﺟﻪ ﺍﻋﺘﻤﺎًﺩﺍ ﻋﻠﻰ ﺍﻟﻤﺴﺎﻓﺔ ﺍﻟﺘﻲ ﻳﺴﺘﻄﻴﻊ ﻓﻴﻬﺎ ﻋﺪ ﺍﻷﺻﺎﺑﻊ‬CF When the pt fails to count fingers, the examiner should move his/her hand close to pt’s face. ‫ ﻳﺠﺐ ﻋﻠﻰ ﺍﻟﻔﺎﺣﺺ ﺍﻭ ﺍﻟﻔﺎﺣﺼﺔ ﺗﺤﺮﻳﻚ ﻳﺪﻩ ﻗﺮﺏ ﻭﺟﻪ ﺍﻟﻤﺮﻳﺾ‬,‫ ﻋﻨﺪﻣﺎ ﻳﻔﺸﻞ ﺍﻟﻤﺮﻳﺾ ﻓﻲ ﻋﺪ ﺍﻻﺻﺎﺑﻊ‬ If pt can appreciate the hand movements, the VA is recorded as HM+ HM+ ‫( ﻛـ‬VA ) ‫ ﺍﺫﺍ ﻛﺎﻥ ﺑﺎﻣﻜﺎﻥ ﺍﻟﻤﺮﻳﺾ ﺗﻘﺪﻳﺮ ﺣﺮﻛﺎﺕ ﻳﺪ ﺍﻟﻔﺎﺣﺺ ﻋﻨﺪﻫﺎ ﻳﺘﻢ ﺗﺴﺠﻴﻞ ﺣﺪﺓ ﺍﻟﺒﺼﺮ‬ Positive Hand movement  If pt cannot distinguish hand movements, the examiner should test whether the pt can perceive light or not ‫ ﻓﻌﻠﻰ ﺍﻟﻔﺎﺣﺺ ﺍﺧﺘﺒﺎﺭﻩ ﻓﻴﻤﺎ ﻟﻮ ﻛﺎﻥ‬, ‫ ﺍﺫﺍ ﻛﺎﻥ ﺍﻟﻤﺮﻳﺾ ﻟﻴﺲ ﺑﺈﻣﻜﺎﻧﻪ ﺍﻟﺘﻤﻴﻴﺰ ﺑﻴﻦ ﺣﺮﻛﺎﺕ ﻳﺪ ﺍﻟﻔﺎﺣﺺ‬ ‫ﺑﺈﻣﻜﺎﻧﻪ ﺗﻤﻴﻴﺰ ﺍﻟﻀﻮﺀ ﺍﻡ ﻻ‬ If yes, vision is recorded as PL+ (perception of light )and if not it is recorded as PL-. PL- ‫ ﻭﺍﺫﺍ ﻛﺎﻧﺖ ﺍﻻﺟﺎﺑﺔ ﻻ ﺗﺴﺠﻞ ﺍﻟﻨﺘﻴﺠﺔ‬, PL+ ‫ ﺍﺫﺍ ﻛﺎﻧﺖ ﺍﻻﺟﺎﺑﺔ ﻧﻌﻢ ﺗﺴﺠﻞ ﺍﻟﻨﺘﻴﺠﺔ‬ PL+ pts must be tested with projection of rays to represent quadrants - nasal, superior, temporal and inferior Then VA is recorded as PL+, PR PL+ ‫ ﺍﻟﻤﺮﻳﺾ ﺫﻭ ﺣﺪﺓ ﺍﻟﺒﺼﺮ‬ ‫ ﻳﺠﺐ ﻓﺤﺼﻪ ﺑﻄﺮﻳﻘﺔ ﺍﺳﻘﺎﻁ ﺍﻻﺷﻌﺔ ﻟﺘﻤﺜﻴﻞ ﺍﻻﺭﺑﺎﻉ ﻛﻤﺎ ﻓﻲ ﺍﻟﺸﻜﻞ‬ PL+,PR ‫( ﻭﺛﻢ ﻳﺘﻢ ﺗﺴﺠﻴﻞ ﺣﺪﺓ ﺍﻟﺒﺼﺮ ﻛـ‬11) Fig.(11) light rays test  PIN HOLE VISUAL ACUITY ‫ﺛﻘﺐ ﺩﺑﻮﺱ ﺣﺪﺓ ﺍﻟﺒﺼﺮ‬ If the vision is subnormal, the visual acuity is again determined by asking the patient to read the letters through a pinhole. To determine if a decrease in vision is correctable by lenses. ‫ ﻳﺘﻢ ﺗﺤﺪﻳﺪ ﺣﺪﺓ ﺍﻟﺒﺼﺮ ﻣﺮﺓ‬، ‫ﺇﺫﺍ ﻛﺎﻧﺖ ﺍﻟﺮﺅﻴﺔ ﻏﻴﺮ ﻃﺒﻴﻌﻴﺔ‬.‫ ﺃﺧﺮﻯ ﺑﺴﺆﺎﻝ ﺍﻟﻤﺮﻳﺾ ﻟﻘﺮﺍﺀﺓ ﺍﻟﺮﺳﺎﺋﻞ ﻣﻦ ﺧﻼﻝ ﺛﻘﺐ‬ ‫ ﻟﺘﺤﺪﻳﺪ ﻣﺎ ﺇﺫﺍ ﻛﺎﻥ ﺍﻻﻧﺨﻔﺎﺽ ﻓﻲ ﺍﻟﺮﺅﻴﺔ ﻳﻤﻜﻦ ﺗﺼﺤﻴﺤﻪ‬ ‫ ﺑﻮﺍﺳﻄﺔ ﺍﻟﻌﺪﺳﺎﺕ‬ The pinhole is a simple way to focus light on retina as well as removing the effects of ‫ﺍﻟﺜﻘﺐ ﻫﻮ ﻭﺳﻴﻠﺔ ﺑﺴﻴﻄﺔ ﻟﺘﺮﻛﻴﺰ ﺍﻟﻀﻮﺀ ﻋﻠﻰ ﺷﺒﻜﻴﺔ ﺍﻟﻌﻴﻦ ﻭﻛﺬﻟﻚ ﺇﺯﺍﻟﺔ آﺛﺎﺭ ﺍﺧﻄﺎﺀ‬ ‫ﺍﻻﻧﻜﺴﺎﺭ‬ Refractive errors such as myopia. Because light passes only through the center of the eye's lens, defects in the shape of the lens (errors of refraction) have no effect while the pinhole instrument is used ‫ ﻓﺈﻥ ﺍﻟﻌﻴﻮﺏ ﻓﻲ ﺷﻜﻞ ﺍﻟﻌﺪﺳﺔ‬، ‫ ﻧﻈًﺮﺍ ﻷﻥ ﺍﻟﻀﻮﺀ ﻻ ﻳﻤﺮ ﺇﻻ ﻣﻦ ﺧﻼﻝ ﻣﺮﻛﺰ ﻋﺪﺳﺔ ﺍﻟﻌﻴﻦ‬.‫ﻣﺜﻞ ﻗﺼﺮ ﺍﻟﻨﻈﺮ‬ ‫)ﺃﺧﻄﺎﺀ ﺍﻻﻧﻜﺴﺎﺭ( ﻟﻴﺲ ﻟﻬﺎ ﺃﻱ ﺗﺄﺛﻴﺮ ﺃﺛﻨﺎﺀ ﺍﺳﺘﺨﺪﺍﻡ ﺃﺩﺍﺓ ﺍﻟﺜﻘﺐ‬ Fig.(12) PIN HOLEVISUAL ACUITY a b