Lecture 9, Lens & Cataract - New PDF

 Crystal-clear biconvex lens.  Lies in the pupillary area behind the iris.  Divides the eyeball into anterior and posterior segments.  Attached to ciliary processes of ciliary body by suspensory ligaments (zonules)....

 Crystal-clear biconvex lens.  Lies in the pupillary area behind the iris.  Divides the eyeball into anterior and posterior segments.  Attached to ciliary processes of ciliary body by suspensory ligaments (zonules).  Covered by a tough capsule that is divided into anterior capsule and posterior capsule, joining each other at the equator.  Anterior capsule is thicker than posterior and lined from its inner surface by anterior subcapsular epithelium.  The posterior capsule is not lined by epithelium.  The center of the anterior capsule is termed anterior pole of the lens while that of the posterior capsule is the posterior pole.  The line joining both poles is the lens axis.  The posterior pole of the lens is the thinnest  The equator is the thickest  The lens cortex formed from the anterior subcapsular epithelium and CRYSTALLINE represents the soft fibers lying inner to the anterior and posterior LENS capsules.  The epithelium proliferation is a continuous process throughout life forming new cortical fibers.  The lens fibers come together to meet at lens sutures.  The lens sutures in front of the nucleus take an erect (Y) shape, while the one behind the lens nucleus is inverted (Y) shape  The lens has 3 nuclei: ① Embryonic nucleus ② Foetal/Infantile nucleus ③ Adult Nucleus   The lens develops embryologically from the surface ectoderm forming a lens placode.  Separates later on forming a lens vesicle.  The lens nucleus present at birth is the embryonic nucleus formed partly by migration of the posterior subcapsular epithelium.  The lens has no blood vessels and no nerve endings.  It was vascular during early embryonic life supplied by the posterior hyaloid artery.  With development, the posterior hyaloid artery obliterates forming tunica vasculosa lentis EMBRYOLOGY   Refraction: about one-third of the refractive power of the eye: ① Dimensions of adult lens:  Lens diameter is about 10 mm.  Lens thickness is about 4 mm. ② The radius of curvature:  Anterior surface is 10 mm.  Posterior surface is 6 mm (more curved) FUNCTION ③ Refractive index:  Cortex: 1.38.  Nucleus: 1.42. ④ Dioptric power:  Inside the eye: 16-18 D.  Outside the eye: 70 D.  Accommodation: that can assist in near vision.  Protection: it protects the retina from harmful ultraviolet (UV) rays   Congenital: Connective tissue diseases.  Acquired: ① Trauma ETIOLOGY ② Hypermature cataract ③ Anterior uveal tumour ④ Large globe (Myopia, Congenital glaucoma)  Visual impairment:  Lenticular myopia SYMPTOMS  Changing astigmatism  Prismatic effect  Monocular diplopia. ① Deep anterior chamber ② Tremulous iris SIGNS ③ Possible visualization of the lens edge or zonules ④ Refraction  Optical correction (Glasses or contact lenses). MANAGEMENT  Surgical Removal.  DEFINITION  Absence of the lens from the pupillary area ① Congenital. ② Surgical. ETIOLOGY ③ Loss through perforated corneal ulcer. ④ Posterior dislocation. ① Strong hypermetropia  +10 to +11 if previously emmetrope  >+11 if previously hypermetrope  Acids  Radiation injury: ③ TRAUMATIC  Ultraviolet  Micowave  Ionizing  Infrared: True exfoliation of lens capsule “Glass blowers cataract”  Electric injury leads to:  Coagulation of lens proteins  IOFB:  Iron lead to sidrosis  Copper lid to Chalcosis and Sun flower’s cataract  ① NUCLEAR CATARACT:  Due to nuclear sclerosis and yellowing  Increase RI of lens nucleus  Leads to 2ry sight (Presbyope can see without reading glasses)  Affect far vision>near  Late may be brown (Brounescent) or black/Nigra) ② POSTERIOR SUBCAPSULAR CATARACT:  Usually axial ④ SENILE  Affect near vision more than far  Affect vision more in bright lightening conditions CATARACT ③ CORTICAL CATARACT: ① Precataractous changes. ② Incipient Cataract :  Incipient means early  Wedge like opacities near the periphery  Affect night vision more than day vision  Leads to mono-ocular diplopia or even polyopia  Leads to haloes around light ③ Immature & Mature Cataract : IMMATURE CATARACT MATURE CATARACT OPACITY  Not total  Total VISUAL ACUITY  CF or better  HM IRIS SHADOW  Present  Absent RR  Dim  Absent COLOR  Grey  White ④ Hypermature Cataract  PRECATARACTOUS CHANGES INCIPIENT CATARACT IMMATURE CATARACT MATURE CATARACT  Morgagian or Shrunken  In shrunke iris shadow and iridodenesis are present LENS INDUCED GLAUCOMA LENS INDUCED UVEITIS LENS DISPLACEMENT INDICATIONS OF ① To improve vision CATARACT ② To treat underlying complications SURGERY ③ To treat underlying retinal disease ① Systemic. ② Local: ③ Fundus examination: EVALUATION BEFORE SURGERY ④ Ultrasound:  ⑤ IOL power calculation:  Using A-Scan US + Keratometry  Local ANESTHESIA  General  ICCE  Performed now in luxated cataract  ECCE  Less vitreous loss  Capsule stand as barrier between aqueous and vitreous  Capsule serve as bag for IOL  Less risk of RD  Less risk of macular edema OPERATIVE PROCEDURE ICCE ECCE  Phacoemulsification  Performed using US  Earlier rehabilitation  Less induced astigmatism PHACOEMULSIFICATION  INTRAOPERATIVE POSTOPERATIVE ① Vitreous loss ① Posterior capsule opacification ② Expulsive Hemorrhage ② Endophthalmitis ③ Corneal edema COMPLICATIONS ④ Astigmatism OF SURGERY ⑤ Iris prolapse ⑥ IOL decentration ⑦ RD ⑧ CME POSTERIOR CAPSULE OPACIFICATION (PCO)