انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة
الكلية كلية الطب
القسم الجراحة
المرحلة 5
أستاذ المادة اسعد جعفر عبد السادة الطائي
4/19/2011 9:14:43 PM
Strabismus (Squint)
Anatomy & Physiology:
Tenon s capsule:
It is a fascial covering to the eyeball & extraocular muscles to facilitate free movement & separate them from intraorbital fat.
Anterior: fuses with the conjunctiva just behind the limbus.
Posterior: separates orbital fat from muscles & globe.
Intermuscular septa: extension of Tenon s, connects muscles.
Check ligaments: connect muscles to overlying Tenon s & insert on orbital walls to support the globe.
Lockwood ligament: fusion of sheaths of inferior rectus (IR) & inferior oblique (IO) muscles; attaches to medial & lateral orbital tubercles to form the hammock support of the eye.
Extra-ocular muscles (EOMs):
MR: adductor
LR: abductor
SR: elevates, adducts & incyclotorts
IR: depresses, adducts & excyclotorts
SO: incyclotorts, abducts & depresses
IO: excyclotorts, abducts & elevates
Definitions:
Fixation: It is the voluntary hold of the visual axis to the object of regard.
Projection: The interpretation of the position of an object on the basis of the retinal elements stimulated.
Binocular single vision (BSV): The coordinated use of the 2 eyes in order to produce a single retinal impression. It is not present at birth, its acquisition depends on the presentation of roughly similar images to eyes which are straight. Advantages of BSV are: enlarged visual field, compensation for the blind spot, one line better visual acuity, & stereopsis.
Grades of BSV:
1- Simultaneous perception.
2- Fusion.
3- Stereopsis.
Retinotopic map: dot by dot representation between the visual field points & retinal points. A similar map is present in the lateral geniculate body, visual cortex, superior colliculus & other areas.
Normal retinal correspondence: every retinal point has got a corresponding point in the retina of the fellow eye having the same projection to the visual space. Foveolae are the first couple of corresponding points.
Panum s fusional area: an oval area surrounding each retinal point which still permits fusion or stereopsis. Double vision will not occur unless a point outside Panum s area is stimulated.
Ocular movements:
Ductions: monocular movements viz. abduction, adduction, elevation, depression, intortion & extortion. They are tested by occluding the fellow eye & asking the patient to follow a target in each direction of gaze.
Versions: binocular movements that are simultaneous & conjugate viz. dextroversion (right), levoversion (left), dextroelevation (right & up), dextrodepression (right & down), levoelevation (left & up), & levodepression (left &down).
Vergences: binocular, simultaneous, disjugate movements viz. convergence & divergence.
Diagnostic positions of gaze: are 9 in number
Cardinal positions of gaze: are 6, movement of eyes in each is governed by a pair of yoke muscles 1 in each eye.
Laws of ocular motility:
Agonist antagonist pairs are muscles of the same eye that move the eye in opposite directions.
Synergists are muscles in the same eye that help the agonist in moving the eye in the given direction.
Yoke muscles are contralateral synergists.
Sherrington s law: increased innervation to an extraocular muscle is accompanied by a reciprocal decrease in innervation to its antagonist.
Hering s law: equal & simultaneous innervation flows to the yoke muscles in versions.
Strabismus: Misalignment of the visual axes.
Causes:
? Sensory factors:
a) Dioptric factors: (1) Opacities of the media. (2) Refractive errors.
b) Retino-neural disturbances.
c) A monocular period: in a child less than 8 years of age.
? Motor factors: these may affect the orbits, extra-ocular muscles and ocular motor cranial nerves pathways &/or nuclei. They include:
(a) Developmental anomalies & birth trauma.
(b) Disease or infection.
(c) Vascular disorders.
(d) Neoplasms.
(e) Trauma.
? Central factors:
(a) Physical or mental illness.
(b) Hyperexcitability.
(c) Hypoexcitability.
(d) Inability to learn.
* Familial & hereditary factors.
Effect:
The presence of a manifest squint may have far reaching effects not only on the development of BSV but also on the vision of the squinting eye, on the actions of the EOMs & even on bodily posture. Among the important sensory effects are:
(a) Pathological diplopia: due to stimulation of non corresponding retinal points.
(b) Confusion: due to the foveal image of the deviating eye.
(c) Suppression: the mental inhibition of visual stimuli, may be: physiological, pathological, facultative or obligatory. It is always a binocular phenomenon.
(d) Amblyopia: Reduced VA not associated with any structural abnormality in the eye or visual pathways, here due to continued monocular obligatory suppression of 1 deviating eye. It is always present even on uniocular examination. It should be sought & treated for successful visual outcome usually by occluding the sound eye as early as possible after diagnosis, since any treatment would be, practically, useless after 8 years of age.
Types of squint:
? Intermittent: only occurs at particular times.
? Constant: occurs at all times.
? Alternating: a constant squint in which fixation alternates between the eyes with no preference for either.
? Unilateral: a constant squint in which only 1 eye, is always preferred for fixation.
? Concomitant (comitant): angle of deviation is constant.
? Inconcomitant (incomitant): angle of deviation is variable.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
|