ملخص مادة الانكسار - PDF

‫‪1446‬‬ ‫ملخص مادة االنكسار‬ ‫الشامل في المادة‬ ‫‪BY AMAN‬‬ 1 :‫المادة النظرية‬ ‫ارجوا مراعاة ان هذه هي مادة المشترك والف...

‫‪1446‬‬ ‫ملخص مادة االنكسار‬ ‫الشامل في المادة‬ ‫‪BY AMAN‬‬ 1 :‫المادة النظرية‬ ‫ارجوا مراعاة ان هذه هي مادة المشترك والفاينل كلها وليست محاضرة واحدة‬ Definition of Strabismus: Strabismus, commonly referred to as eye misalignment or misaligned eyes, is a condition in which the eyes fail to align properly when focusing on an object. In normal vision, both eyes are parallel and work together to produce a single, clear, and three- dimensional image. This coordination is essential for depth perception and binocular vision, where the brain combines input from both eyes into a unified visual field. However, in individuals with strabismus, this synchronized function is disrupted, and one eye deviates while the other remains fixed on the object. This deviation can occur in different directions—inward (esotropia), outward (exotropia), upward (hypertropia), or downward (hypotropia). Further Details on Eye Misalignment: 1. Constant vs. Intermittent Misalignment: o A constant deviation indicates a persistent muscle or nerve issue. o Intermittent strabismus may surface during times of fatigue, illness, or visual stress. It is often seen in cases of exotropia where eye drift occurs when viewing distant objects. 2. Unilateral vs. Alternating: o In unilateral strabismus, the misalignment consistently affects the same eye, potentially leading to amblyopia (lazy eye). o Alternating strabismus shifts the deviation between both eyes, reducing the risk of amblyopia but impairing binocular vision and coordination. Impact of Strabismus on Visual Function: Misaligned eyes send two different images to the brain, which disrupts the ability to merge them into a single image (fusion). In adults, this typically causes double vision (diplopia), where overlapping or disjointed images make visual tasks challenging. In children, the brain adapts by suppressing the image from the misaligned eye, which reduces confusion but can lead to amblyopia. Amblyopia occurs when the visual cortex stops processing input from the deviating eye, resulting in permanently reduced vision if not corrected early. Underlying Causes of Strabismus: 1. Extraocular Muscle Imbalance: o The six extraocular muscles control eye movement and alignment. Dysfunction in these muscles causes deviations in one or more directions. o Example: Overaction or tightness of the medial rectus muscle contributes to esotropia, while weakness in the lateral rectus muscle causes exotropia. BY AMAN ‫ملخص مادة االنكسار‬ 2 2. Cranial Nerve Disorders: o Eye muscle function relies on three cranial nerves:  Oculomotor nerve (CN III): Controls most rectus muscles and the inferior oblique muscle.  Trochlear nerve (CN IV): Innervates the superior oblique muscle, crucial for downward movement.  Abducens nerve (CN VI): Activates the lateral rectus muscle for outward movement. o Damage to these nerves, due to trauma, stroke, tumors, or systemic diseases, can result in paralytic strabismus, where eye movement is restricted. 3. Refractive Errors: o Significant farsightedness (hyperopia) forces excessive focusing, which can trigger accommodative esotropia, a common type of strabismus in children. 4. Neurological and Systemic Conditions: o Conditions such as cerebral palsy, Down syndrome, and brain injuries can interfere with the coordination of eye muscles and brain signals. o Systemic diseases like diabetes may cause cranial nerve palsies leading to eye misalignment. Impact on Visual Function and Quality of Life: Strabismus is not merely a cosmetic issue. In children, untreated strabismus can lead to developmental delays in visual processing, motor skills, and hand-eye coordination. Poor depth perception and limited peripheral vision can hinder performance in activities such as sports or reading. Social and psychological effects are also significant, as children may face teasing or reduced self-esteem due to visible misalignment. In adults, sudden-onset strabismus causes functional limitations due to double vision, making routine tasks such as reading, driving, and navigating spaces difficult. Patients often experience dizziness, headaches, and visual fatigue, significantly impairing their quality of life. In both children and adults, compensatory head tilting or turning is often observed as a natural adaptation to reduce visual strain or diplopia. Strabismus is a complex condition that requires prompt and individualized treatment. By addressing the underlying causes and implementing corrective measures early, functional vision can be preserved, and quality of life can be significantly improved. Classification and Differences Between Heterophoria and Heterotropia in Strabismus: Heterophoria (Latent Strabismus):  Heterophoria is a latent eye misalignment that remains controlled by the brain's fusion mechanism under normal conditions, maintaining binocular single vision. It becomes noticeable only when fusion is disrupted, such as during monocular viewing (e.g., when one eye is covered). Types: BY AMAN ‫ملخص مادة االنكسار‬ 3  Esophoria (inward deviation), Exophoria (outward), Hyperphoria (upward), and Hypophoria (downward). Symptoms:  Often asymptomatic but may cause eye strain, headaches, and intermittent double vision during visual fatigue, prolonged near tasks, or reading. Diagnosis:  Detected with the Cover-Uncover Test or Alternate Cover Test.  Measured using prisms or the Maddox Rod Test. Management:  Correct refractive errors with glasses.  Use prisms to reduce symptoms.  Perform vision therapy to strengthen fusion and improve binocular stability. Heterotropia (Manifest Strabismus):  Heterotropia is a visible misalignment of the eyes that occurs because the brain's fusion mechanism fails to control ocular alignment. The deviation is constant or intermittent, even when both eyes are open. Types:  Esotropia (inward turn), Exotropia (outward), Hypertropia (upward), and Hypotropia (downward). Symptoms:  In children: Risk of amblyopia (lazy eye) due to suppression.  In adults: Double vision (diplopia), eye strain, or abnormal head posture to minimize symptoms.  Loss of binocular vision and depth perception. Diagnosis:  Measured using the Cover Test, Krimsky Test with prisms, and ocular motility testing.  Sensory adaptations can be identified with tools like the Synoptophore. Management:  Correct refractive errors (e.g., glasses for accommodative esotropia).  Use patching therapy for amblyopia in children.  Prisms for temporary symptom relief.  Surgery for significant deviations.  Vision therapy to improve eye coordination and binocular function. Types and Diagnosis of Strabismus Based on the Direction of Deviation: A. Based on the Direction of Deviation: 1. Esotropia: o Definition: Inward turning of the eye. o Advanced Insight: This can be constant (present all the time) or intermittent. BY AMAN ‫ملخص مادة االنكسار‬ 4 o Accommodative esotropia occurs due to uncorrected hyperopia, causing overfocusing and eye crossing. o Unique Considerations: Infants with congenital esotropia often have a large-angle deviation, whereas acquired esotropia may signal underlying neurological issues. 2. Exotropia: o Definition: Outward turning of the eye. o Advanced Insight: Exotropia is more noticeable when a person is tired or daydreaming. It may be intermittent initially but can become constant without treatment. o Unique Considerations: Divergence excess exotropia, where the eyes drift more during distance fixation, requires special diagnostic evaluation. 3. Hypertropia and Hypotropia: o Definition: Vertical misalignment where the eye turns upward (hypertropia) or downward (hypotropia). o Unique Insight: Often caused by superior oblique palsy (cranial nerve IV dysfunction) or trauma. Vertical misalignments are less common but more symptomatic, causing significant diplopia. B. Based on the Cause (Etiology): 1. Accommodative Esotropia: o Occurs primarily due to excessive accommodation (focusing effort) triggered by hyperopia (farsightedness). o Refractive Accommodative Esotropia:  Occurs in patients with moderate to high uncorrected hyperopia (typically +2.00 D to +6.00 D).  Excessive accommodation induces excessive convergence, resulting in inward eye deviation.  Characteristics: Usually manifests between 2-3 years of age, gradual onset, and intermittent at first.  Symptoms: Eyestrain, blurred vision, and intermittent diplopia, particularly during near tasks.  Management: Optical correction with glasses or contact lenses to reduce accommodative demand and prevent convergence excess. o High AC/A Ratio Accommodative Esotropia:  A high Accommodative-Convergence/Accommodation (AC/A) ratio leads to excessive convergence even with minimal accommodation effort.  This type of esotropia is more prominent during near fixation compared to far fixation.  Management: Bifocal lenses or progressive addition lenses (PALs) to reduce near-point accommodative demand. 2. Sensory Strabismus: BY AMAN ‫ملخص مادة االنكسار‬ 5 oLoss of vision or poor sensory fusion in one eye leads to secondary strab ismus. o Causes: Congenital cataracts, optic nerve hypoplasia, retinal disease, or anisometropia. o Common Types: Sensory esotropia or exotropia, depending on age of onset. 3. Consecutive Strabismus: o Refers to a post-surgical or post-traumatic change where an initial deviation (e.g., exotropia) reverses into another direction (e.g., esotropia). o Management: Wait-and-see approaches for small angles; prisms or further surgery for larger deviations. 4. Paralytic Strabismus: o Definition: Misalignment caused by nerve palsy affecting extraocular muscles. o Unique Insight: Cranial nerve III palsy causes ptosis, outward deviation, and pupil dilation, while cranial nerve VI palsy affects lateral rectus function, causing esotropia. C. Based on the Magnitude of Deviation: 1. Microtropia: o A small-angle, often unnoticed, form of strabismus. o Characteristics: Minimal misalignment, reduced stereopsis (depth perception), and visual suppression in the misaligned eye. o Clinical Concern: Despite its small angle, microtropia may cause amblyopia (lazy eye) and reduced binocular function. 2. Large-angle Strabismus: o The term "large angle of deviation" refers to a noticeable and measurable eye misalignment, where the angle of strabismus is greater than 20 prism diopters. o Symptoms:  Amblyopia (lazy eye) in children if untreated.  Diplopia (double vision) in older children and adults.  Loss of binocular vision (stereopsis/depth perception).  Eyestrain or compensatory head posture to minimize misalignment. Calculation of the AC/A Ratio: The AC/A ratio measures the relationship between the amount of accommodative convergence (AC) and the accommodation (A) exerted.  Gradient Method: Measure the deviation with and without a +1.00 D or +2.00 D lens at a fixed distance (e.g., 33 cm). The difference in the deviation gives the AC/A ratio. o Formula: AC/A = (Deviation without lens - Deviation with lens) / Lens Power  Calculated Method: Use the patient's distance and near deviation along with the interpupillary distance (IPD). o Formula: AC/A = IPD (in cm) + (Near deviation - Distance deviation) / Near fixation distance in meters. BY AMAN ‫ملخص مادة االنكسار‬ 6 When to Calculate the AC/A Ratio:  AC/A ratios are particularly useful in diagnosing high AC/A accommodative esotropia and other strabismus conditions associated with near-fixation challenges.  It helps distinguish between basic esotropia and convergence excess esotropia.  For example, a significantly higher AC/A ratio indicates convergence excess, requiring specialized management such as bifocal lenses or progressive lenses to alleviate near fixation issues. Clinical Benefits of Knowing the AC/A Ratio:  Determines the role of excessive convergence in esotropia.  Guides appropriate optical correction (bifocals or progressive lenses).  Helps predict outcomes for non-surgical and surgical interventions.  Identifies patients at risk of developing esotropia during near work. Practical Example:  Patient 1: A 5-year-old child presents with a near deviation of 30 prism diopters and a distance deviation of 10 prism diopters. Using the calculated method and an IPD of 5.5 cm, the AC/A ratio is determined as follows: o Formula: AC/A = 5.5 + (30 - 10) / 0.33 o Diagnosis: The high AC/A ratio indicates convergence excess esotropia, requiring bifocal lenses to address near fixation strain.  Patient 2: An 8-year-old presents with similar symptoms but has a balanced deviation of 20 prism diopters at both near and distance. The AC/A ratio is normal, indicating basic esotropia requiring optical correction only. D. Strabismus Classification Based on Variation in Horizontal Deviation with Vertical Gaze: A and V Patterns: 1. A-Pattern Strabismus: o Horizontal deviations (esotropia or exotropia) increase in up-gaze and decrease in down-gaze. o Example: A-pattern esotropia shows greater inward deviation in upgaze. 2. V-Pattern Strabismus: o Horizontal deviations increase in down-gaze and decrease in up-gaze. o Example: V-pattern exotropia involves greater outward deviation when looking upward. Clinical Significance:  A and V patterns indicate oblique muscle dysfunction or abnormal innervation and influence surgical planning. BY AMAN ‫ملخص مادة االنكسار‬ 7 E. Cyclovertical Deviations:  Cyclovertical deviations are a type of strabismus based on the involvement of vertical and torsional misalignments of the eyes. These deviations occur due to dysfunction of the oblique muscles and/or vertical rectus muscles, leading to vertical (hyper or hypo) and torsional (cyclo) misalignment. Types:  Hyperdeviation: One eye deviates upward relative to the other.  Cyclodeviation: The affected eye rotates around its visual axis. Symptoms: Diplopia, eyestrain, and nausea. Clinical Importance: Common in trauma, cranial nerve palsies, and mechanical restrictions. F. Primary Comitant Esotropia (PCE) and Primary Comitant Exotropia (PCX):  These are based on the relationship between the magnitude of deviation and the fixation distance (distance versus near). The classification is determined by comitancy (equal deviation in all gaze directions) and the behavior of the deviation at different fixation distances. 1. Primary Comitant Esotropia (PCE): o Basic Esotropia: Equal deviation at distance and near. o Divergence Insufficiency: Greater esotropia at distance than near. 2. Primary Comitant Exotropia (PCX): o Basic Exotropia: Equal deviation at distance and near. o Divergence Excess: Greater exotropia at distance. Prescribing Glasses for Myopia/Hyperopia with Strabismus: 1. Hyperopia + Esotropia: o Hyperopia worsens esotropia due to excessive accommodation and convergence. o Solution: Prescribe full hyperopic correction to relax accommodation. For patients with a high AC/A ratio, use bifocals (+2.00 D or +3.00 D add) for near tasks. 2. Myopia + Esotropia: o Myopia has minimal impact on esotropia. o Solution: Prescribe the full myopic correction to optimize distance vision. 3. Myopia + Exotropia: o Reduced accommodation in myopia weakens convergence, worsening exotropia. o Solution: Prescribe full myopic correction to stimulate convergence. In some cases, a slight undercorrection helps improve alignment. 4. Hyperopia + Exotropia: o Hyperopia may naturally stimulate convergence, reducing exotropia. o Solution: Prescribe the full hyperopic correction. If exotropia persists, consider over-minus lenses temporarily to encourage convergence. 5. Prisms: BY AMAN ‫ملخص مادة االنكسار‬ 8 o Use base-in prisms for exotropia and base-out prisms for esotropia to ease alignment efforts when refractive correction alone is insufficient. 6. Bifocals: o In accommodative esotropia with a high AC/A ratio, prescribe bifocal lenses to reduce near-point convergence strain. 7. Follow-Up: o Regular follow-ups are critical, especially in children, to monitor changes in refractive error, ocular alignment, and visual function. Diagnostic Methods for Strabismus: 1. Hirschberg Test (Corneal Light Reflex Test): o A quick and qualitative method to assess the presence and approximate severity of strabismus. o A light source is directed at the patient's eyes from a distance of about 33 cm, and the examiner observes the position of the corneal light reflex. o In strabismus, the reflex is displaced in the deviating eye, indicating the type of misalignment. 2. Krimsky Test: o A more quantitative measurement of ocular misalignment using prisms. o A prism bar is placed in front of the fixating eye, and the strength of the prism is gradually increased until the corneal light reflex is symmetrically centered in both eyes. 3. Alternate Cover Test: o The gold standard for detecting and measuring manifest deviations (tropias) and latent deviations (phorias). o The examiner alternately covers each eye while the patient fixates on a target at distance or near. Any movement of the uncovered eye to regain fixation indicates the presence of a deviation. 4. Cycloplegic Refraction: o Performed to identify refractive errors, particularly in cases of accommodative esotropia. o Cycloplegic drops such as cyclopentolate or atropine are used to temporarily paralyze the ciliary muscle, eliminating accommodation. 5. Ocular Motility Testing: o Evaluates the function of the extraocular muscles by assessing eye movements in all nine cardinal positions of gaze (up, down, right, left, and diagonals). Neuroimaging (MRI/CT):  Purpose: Neuroimaging, including MRI (Magnetic Resonance Imaging) or CT (Computed Tomography), is used when strabismus is suspected to have a neurological or structural cause. BY AMAN ‫ملخص مادة االنكسار‬ 9  MRI: Particularly useful for evaluating cranial nerve palsies (e.g., CN III, IV, or VI), brainstem lesions, or tumors affecting ocular alignment.  CT: Preferred for detecting structural abnormalities such as orbital trauma, fractures, or restrictive strabismus, as seen in thyroid eye disease.  Clinical Importance: Neuroimaging is essential for cases of paralytic strabismus, incomitant deviations, or when neurological symptoms accompany strabismus. Maddox Rod Test:  Purpose: A simple method to detect and differentiate phorias (latent deviations) and tropias (manifest deviations).  Procedure: A Maddox rod (a cylindrical lens) is placed over one eye, and the patient fixates on a light source. The rod converts the light into a streak, and the examiner notes the position of the streak relative to the light.  Applications: o Identifies horizontal, vertical, or torsional deviations. o Helps determine esophoria/exophoria, hyperphoria/hypophoria, or cyclophoria.  Clinical Use: Particularly useful for diagnosing subtle or latent deviations. Prism Cover Test:  Purpose: Combines the precision of prism measurement with the alternate cover test to quantify the angle of deviation.  Procedure: Prisms are placed over the deviating eye, and the examiner observes eye movement during the cover-uncover procedure. The strength of the prism is adjusted until the eye no longer moves, effectively neutralizing the deviation.  Clinical Use: Provides an exact measurement of the strabismus angle in prism diopters and is critical for planning surgical correction. Synoptophore (Major Amblyoscope):  Purpose: A specialized instrument used to evaluate binocular vision, fusion, suppression, and stereopsis (depth perception).  Procedure: The patient views two separate images presented to each eye, and the examiner assesses the patient's ability to align and fuse these images into a single perception.  Clinical Use: Measures the angle of deviation and identifies abnormal retinal correspondence (ARC) or suppression. It is a valuable tool for understanding sensory adaptations in strabismus. Bagolini Striated Glasses Test:  Purpose: Evaluates binocular single vision (BSV) and detects suppression or diplopia. BY AMAN ‫ملخص مادة االنكسار‬ 10  Procedure: The patient wears glasses with striated lenses and fixates on a single light source, which appears as cross-like streaks. The patient's perception of the streaks helps determine the presence of normal binocular vision, suppression of one eye, or diplopia.  Clinical Use: Particularly sensitive for detecting subtle sensory abnormalities. Double Maddox Rod Test:  Purpose: Used to measure torsional deviations (cyclotropia).  Procedure: Two Maddox rods are placed at 90° to each other, one for each eye, and the patient aligns the perceived light streaks. Any misalignment of the streaks indicates the degree and direction of torsional deviation, such as incyclotropia or excyclotropia.  Clinical Use: Especially useful for diagnosing cyclodeviations caused by superior oblique palsy or other oblique muscle dysfunction. Worth Four-Dot Test:  Purpose: Evaluates binocular vision and detects suppression or diplopia.  Procedure: The patient wears red-green glasses and fixates on a light source with four dots (red, green, and white). The number and color of dots perceived help identify normal binocular vision, suppression of one eye, or diplopia.  Clinical Use: Provides insights into binocular function. Hess Screen Test:  Purpose: Evaluates ocular muscle function by plotting eye positions in all directions of gaze.  Procedure: The patient wears red-green glasses and fixates on lights on a screen while deviations are recorded. The plotted results help identify weak or overacting muscles.  Clinical Use: Particularly useful for diagnosing paralytic strabismus or incomitant deviations. Forced Duction Test:  Purpose: Differentiates between restrictive strabismus (e.g., mechanical restriction) and paralytic strabismus (nerve-related).  Procedure: Under topical anesthesia, the examiner manually moves the eye to assess resistance. Resistance indicates a mechanical restriction, such as in thyroid eye disease, while free movement points to a neurological cause.  Clinical Use: Helps in determining the underlying cause of strabismus. Summary of Diagnostic Methods: BY AMAN ‫ملخص مادة االنكسار‬ 11  Basic Tests: Hirschberg, Krimsky, and Cover Tests identify and measure misalignment.  Refractive Tests: Cycloplegic refraction addresses refractive causes.  Muscle Function Tests: Ocular motility testing evaluates muscle function.  Neurological Tests: Neuroimaging identifies neurological or structural abnormalities.  Advanced Tests: Maddox Rod, Synoptophore, Worth Four-Dot Test, and Hess Screen detect sensory and motor anomalies. Together, these methods ensure a comprehensive diagnosis and guide effective management strategies for strabismus. Correction of Strabismus: Non-Surgical Treatments: 1. Eyeglasses or Contact Lenses: o Correct underlying refractive errors, particularly hyperopia in accommodative esotropia. o Bifocal lenses may be prescribed for near-distance misalignments. 2. Prism Lenses: o Prisms displace images, compensating for misalignment and reducing diplopia without addressing the underlying cause. 3. Vision Therapy (Orthoptics): o Includes eye exercises to strengthen ocular muscles, improve convergence, and enhance binocular function. o Particularly useful for intermittent exotropia and convergence insufficiency. 4. Botulinum Toxin (Botox) Injections: o Temporarily paralyzes overacting muscles to allow weakened muscles to recover. o Particularly effective for acute paralytic strabismus. Surgical Treatments: 1. Recession Surgery: o Weakens an overacting muscle by repositioning it posteriorly on the sclera. 2. Resection Surgery: o Strengthens a weak muscle by shortening it. 3. Adjustable Suture Technique: o Fine-tunes muscle alignment post-operatively under conscious sedation, allowing precise correction. 4. Vertical Muscle Surgery: o Required for hypertropia or hypotropia caused by oblique muscle palsy or overaction. BY AMAN ‫ملخص مادة االنكسار‬ 12 Post-Treatment Care:  Follow-up Assessments: Regular check-ups ensure alignment stability and detect residual amblyopia.  Vision Therapy: Often recommended post-surgery to maintain binocular vision.  Secondary Surgeries: May be required in complex or recurring cases. Low Vision: Definition of Low Vision:  WHO Definition: Low vision is defined as a condition where a person has presenting visual acuity in the better eye of 6/18 to 3/60, even with the best possible correction or treatment.  Characteristics: Includes significant visual impairment that affects daily functioning but does not meet the threshold for total blindness. Individuals with low vision retain some usable residual vision that can be enhanced with rehabilitation, optical devices, and assistive tools. Types of Vision Loss: 1. Normal Vision: o Visual acuity ranging between 6/6 and 6/12. o Individuals can perform daily tasks without restrictions. 2. Early Visual Impairment (EVI): o Visual acuity between