Lens

Lens

Lu Yong Department of ophthalmology First Teaching Hospital of Zhengzhou University

Anatomy 

Shape    

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a biconvex lens and capable of changing shape colorless transparent avascular

size 4mm thick and 9mm in diameter

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position 

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behind the iris and the pupil In front of the vitreous suspended by suspensary ligament

Lens

Anatomy 

structure 

capsule:an elastic transparent basement membrane admit water and electrolytes pass through the lens fibers are enveloped in it epithelium : this single cell layer located anteriorly and extending to the equator

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fibers:continuously produced by epthelium the nucleus:old fibers ,harder at the centre the cortex: new fibers,softer, at the periphery

With age,the lens gradually becomes larger, harder and less elastic

Physiology 

composition  

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water -64% The water content of the lens decreases with age. protein -35% the highest protein content in any body tissue  soluble protein  insoluble protein:With age, the percent of it increases 1%- A trace of minerals are present (Potassium, Ascorbic acid and Glutathione) The lens has complex metabolic process. It`s nourishment comes from aqueous humor.When there are changes of aqueous or capsule or metabolism,the transparent lens becomes opaque.

Physiology 

Function   

one of important refractive medias focus light rays upon the retina filter a part of ultraviolet rays ,it is beneficial to the retina

Cataract 

Cataract –transparent lens becomes opaque

Cataract 

Epidemiology 

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Cataract is a common ocular disease and one of the main causes of blindness.It is estimated that 30 to 45 million people in the world are blind,with cataract accounting for as much as 45% of this blindness. The prevalence of cataract varies widely with striking regional differences.It is more common in areas where people eyes expose to sunlight greatly. The prevalence rises with age and is higher in females. WHO defines blindness as best corrected visual acuity less than 20/400(0.05) or visual field restricted to 10°or less.

Classification  

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Senile cataract-age related cataract Complicated cataract-due to ocular inflammation or degeneration affects lens metabolism Congenital cataract-a result of developmental disturbance of lens during the process of development of fetus Traumatic cataract-eye trauma cause lens opacities Metabolic cataract-metabolic disturbance Toxic cataract-many drugs and chemicals have been shown to induce cataracts After-cataract-after cataract surgery,remained cortex and epithelial cells exfoliated to form opacity

Senile cataract Senile cataract is by far the most common type. It often occurred over the age of 40. With aging,it`s incidence increases.we call it “age related cataract” 

Etiology

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It is a lens disorder formed on the basis of decreasing of lens metabolic function with aging of whole body and plus many other factors. It has relation to Heredity Ultraviolet rays-plateau (expanse of level land high above sea-level) long periods of strong sunlight Systematic disorders-diabetes Nourishment condition

map

Senile cataract 

Clinical findings 

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Symptom:progressively blurred vision is the only symptom Types:according to the place of opacity appear first   

Cortical cataract Nuclear cataract Posterior subcapsular cataract

Senile cataract-cortical cataract There are 4 stages in its developing 

Incipient stage (beginning;in an early stage)  

The lens is only slightly opaque These spoke-like opacities

begin in the lens periphery  

Pupillary area isn`t affected No blurred vision takes place

Senile cataract-cortical cataract 

Intumescent stage (immature stage) 

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Lens opacity develop gradually,the fibers absorb water,the lens edema,the cortex become swollen. The anterior chamber is shallow .

It is easy to induce onset of glaucoma. 

Visual acuity

decrease.

Senile cataract –cortical cataract 

Mature stage   

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The lens is completely opaque, The color is greywhite. The depth of the anterior chamber restores to normal. Because the swollen decreases. The vision is obviously decreased to FC or HM

Senile cataract-cortical cataract 

Hypermature stage 

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The degenerated cortex has been decomposed to form milklike substance. The lens nucleus fall down. The capsule wrinkled and shrunk. Due to water escaping from lens.

Senile cataract-nuclear cataract 

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The nucleus becomes harder(sclerotic) and increasingly pigmented with age. At beginning, nucleus appears yellowish,its color becomes more and more dark with development

It generally produce more blurring of distance vision than near vision

Senile cataractposterior subcapsular cataract 

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Golden yellow or white particles,mixed with small vacuoles in them occur at shallow layer of subcapsular cortex in posterior pole lens. The opaque area situates in the area of visual axis,so blurred vision takes place in early stage

Congenital cataract It is a result of developmental disturbance of lens during the process of development of fetus  Etiology 

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Genetic factor-autosomal dominant inheritance Damage of fetal lens caused by systemic disorders of mother or fetus-viral infections,nourishment and metabolic disturbance of mother

Congenital cataract 

Commonly are as follows: 

polar cataract,nuclear cataract,lamellar cataract,complete cataract,coronary cataract

axiality cataract

Complicated cataract 

It is a lens opacity induced by ocular inflammation or degeneration disorder

Uveitis,glaucoma,too low IOP,retinal pigmentary degeneration

Traumatic cataract It may be caused by mechanical injury,physical forces(radiation,electrical current,heat and cold),and osmotic influences

Penetrating cataract

Metabolic cataract  

Diabetic cataract Hypocalcemic cataract

Toxic cataract and After cataract 

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Many drugs and chemicals have been shown to induce cataractAfter cataract surgery,remained cortex and epithelial cells exfoliated onto lens posterior capsule proliferate to form opacity

Management of cataract 

Medical management 

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No medical treatment has been proven conclusively to delay,prevent,or reverse the development of cataract

Indication for surgery 

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The most common indication for cataract surgery is the patient`s desire for improved visual function. When visual acuity impairment interferes with the patient`s normal activities,the surgery of cataract well be performed.

Lens surgery 

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Microsurgical techniques is employed for all cataract surgery. There are 3 principal types of lens extraction 

Intracapsular cataract extraction(ICCE) 

It involves complete removal of the lens within its capsule.

through a larger (12mm length) superior limbal incision 

The larger incision may increase the risk of wound-related problems.

Lens surgery 

Extracapsular cataract extraction(ECCE) 

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It involves removal of the lens nucleus and cortex through an opening in the anterior capsule, leaving the posterior capsule in place. A superior limbal incision is made,it is shorter than ICCE The anterior portion of the capsule is ruptured and removed The nucleus is extracted The cortex is either irrigated or aspirated from the eye leaving the posterior capsule behind.

ECCE and IOL

IOL

Lens surgery 

Phacoemulsification(Phaco) 

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It is a relatively new technique.In recent years, it has become popular. It is a method of extracting the nucleus through a small incision(3mm). The nucleus is extracted by ultrasonic vibration. This technique results in a lower incidence of woundrelated complications, faster healing, and more rapid visual rehabilitation than procedures requiring larger incisions.

Phaco

ICCE vs ECCE vs Phaco TYPE ICCE

ECCE

Phaco

ADVANTAGES

DISADVANTAGES

Removes all lens material, no posterior capsular opacity

Larger incision Cystoid macular edema Vitreous complications Endophthalmodonesis Increased incidence of RD Posterior capsule opacity

Smaller incision No vitreous complications Less endophthalmodonesis Less CME,RD Allows implants pcIOL Smallest incision Demanding technique Less induced astigmatism Complications while learning Fastest technique

Visual rehabilitation 

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Removal of the lens causes a marked reduction of the refractive power of the eye,we call it aphakia Aphakia may be corrected by three methods include spectacles(glasses),contact lens or intraocular lens(IOL) to increase its refractive power IOL is the best among them and now is widely used in the world

Correction of Aphakia TYPE Spectacles

Contact lens

ADVANTAGES Safety Cheaper Convenience Less image magnification (7%~12%)

DISADVANTAGES Magnification of image size (20%-35%) Spherical aberration Difficult insertion and removal Need for disinfection and cleaning systems Toxic and inflammatory phenomena

Intraocular lens Least image magnification (1%~2%) Least optical distortion

Less aniseikonia