Cataract
Definition

∑ Any opacity of the lens or loss of transparency of the lens that causes diminution or impairment of vision is called Cataract.

∑ Although any lens opacity whether or not it leads to decrease in vision is technically cataract, yet an opacity in the periphery of the lens, which is stationary and not hampering vision should be diagnosed just Lens Opacity in order to avoid causing unnecessary anxiety to the patient.
Classification



Etiological



Morphological



Stage of Maturity



Chronological
Etiological Classification
1. 1. Senile
2. 2. Traumatic



Penetrating



Concussion (Rosette Cataract)



Infrared irradiation (Glass Blowerís Cataract)



Electrocution



Ionizing Radiation
3. 3. Metabolic



Diabetes (Snow Storm Cataract)



Hypoglycaemia



Galactosemia (Oil Drop Cataract)



Galactokinase Deficiency



Mannosidosis



Fabryís Disease



Loweís Syndrome



Wilsonís Disease (Sunflower Cataract)



Hypocalcaemia
4. 4. Toxic



Corticosteroids



Chlorpromazine



Miotics



Busulphan



Gold



Amiodarone
5. 5. Complicated



Anterior Uveitis



Hereditary Retinal & Vitreoretinal Disorders



High Myopia



Glaucomflecken



Intraocular Neoplasia
6. 6. Maternal Infections



Rubella



Toxoplasmosis



Cytomegalovirus
7. 7. Maternal Drug Ingestion



Thalidomide



Corticosteroid
8. 8. Presenile Cataract



Myotonic Dystrophy



Atopic Dermatitis (Syndermatotic Cataract)



GPUT & GK Enzyme Deficiencies
9. 9. Syndromes with Cataract



Downís Syndrome



Wernerís Syndrome



Rothmundís Syndrome



Loweís Syndrome
10. 10. Hereditary
11. 11. Secondary Cataract

∑ After-Cataract (after the cataract surgery)
Morphological Classification
1. 1. Capsular



Congenital (Anterior Polar & Posterior Polar)



Acquired
2. 2. Subcapsular



Posterior Subcapsular (Cupuliform)



Anterior Subcapsular
3. 3. Nuclear



Congenital (Discoid, etc.)



Senile
4. 4. Cortical



Congenital (Coronary, Coralliform, etc)



Senile (Cuneiform)
5. 5. Lamellar or Zonular
6. 6. Sutural
7. 7. Others



Blue-Dot (Cataracta caerulea)



Membranous



Cataracta Pulveranta Centralis



Reduplicated Cataract
Stage of Maturity
1. Immature
2. Mature
3. Intumescent
4. Hypermature
5. Morgagnian
Chronological
1. Congenital (since birth)
2. Infantile (first year of life)
3. Juvenile (1 to 13 years of life)
4. Presenile (13 to 35 years of life)
5. Senile
Pathogenesis

Two main pathogenetic processes are involved in most (especially senile) cataract:
1. Hydration
2. Sclerosis
Hydration



Increased hydration leads to lamellar separation and collection of protein-deficient fluid between lens fibers.



Leads to increased scattering of light and loss of transparency.



Hydration also leads to denaturation of lens proteins and results in irreversible opacification.



Mechanisms of increased hydration are:

1. Failure of active pump mechanism
2. Increased leakage across posterior or anterior capsule
3. Increased Osmotic pressure

Sclerosis



This process is seen mostly in senile cataract and involves predominantly the nucleus.



Increased compaction of lens proteins and fibers due to inter-lamellar binding of proteins by sulfide bonds.



Resultant aggregates of very high molecular weight proteins lead to increased scattering of light and loss of transparency.



It is part of normal aging phenomenon.
Senile Cataract
Epidemiology
Global



38 million people are blind



41 % because of cataract
National



71 % of blindness in Nepal is because of cataract



About 72 % of blindness in India is caused by Cataract
Progression
I. I.Stage of Lamellar Separation



Hydration leads to separation of cortex from nucleus



Appreciated on slit lamp biomicroscopy
II. II. Stage of Incipient Cataract



Early opacities appear



Vision unaffected but other symptoms e.g., glare, appear.
III. III. Immature Cataract

∑ Opacification leading to diminution of vision.

∑ Two morphological forms are seen:

1. 1. Cuneiform Cataract: Wedge shaped opacities appear in the peripheral cortex and progress towards the nucleus. Vision is worse in low ambient illumination when the pupil is dilated.

2. 2. Cupuliform Cataract: A disc or saucer shaped area of the cortex beneath the posterior capsule undergo opacification. The opacity being central, the vision is worst in bright ambient illumination when the pupil is constricted.



Lens appears grayish white in color.



Iris shadow can be seen on the opacity with oblique illumination.
IV. IV. Intumescent Cataract



Sometime during the course maturation the lens imbibes lot of fluid and becomes swollen.



Anterior chamber becomes shallow.



Angle of anterior chamber may close resulting in glaucoma (Phacomorphic Glaucoma).
V. V. Mature Cataract



Entire cortex becomes opaque.



Vision reduced to just perception of light



Iris shadow is not seen



Lens appears pearly white.
VI. VI. Hypermature Cataract

∑ This may take any of two forms:

1. 1. Liquefactive or Morgagnian Type: The cortex undergoes auto-lytic liquefaction and turns uniformly milky white. The nucleus loses support and settles to the bottom.

2. 2. Sclerotic Cataract: The fluid from the cortex gets absorbed and the lens becomes shrunken. There may be deposition of calcific material on the lens capsule. Anterior chamber deepens and iris becomes tremulous (Iridodonesis). The zonules become weak increasing the risk of subluxation / dislocation of lens.



Liquefied cortex may leak out of the lens resulting in either uveitis or glaucoma (Phacolytic Glaucoma).



Very rarely the entire cortex and nucleus can get completely liquefied and absorbed leaving behind clear anterior and posterior capsules (Pseudo-aphakia). Vision improves to about finger counting at 1 meter.
Nuclear Cataract

∑ Goes through stage of immaturity and maturity but never becomes intumescent or hypermature.

∑ Urochrome or melanin pigment deposition may take place giving nucleus a typical color:



Yellow



Black (Cataracta nigra)



Brown (Cataracta brunescnence)



Red (Cataracta rubra)

∑ In early stages there is shift of refraction towards myopia. This improves the near vision of the patient. Consequently the patient who so far required thick near glasses for reading, can read small print easily without them (phenomenon of Second Sight).
Clinical Presentation
Symptoms

1. Glare: When patient looks at a point source of bright light the diffusion of white and colored light around it drastically reduces vision. Night driving becomes especially troublesome. Posterior subcapsular cataract (cupuliform) notably causes disabling glare.
2. Image Blur: Opacification of lens leads to diminution of vision which is characteristically painless and progressive (& does not improve with pin-hole). From a normal of 6/6 the vision continues to deteriorate as the cataract progresses, but as long as the cataract is immature patient will at least be able to count fingers. When cataract matures the vision is reduced to barely perception of light. In hypermature, rarely, the vision may improve a little if the cortex gets absorbed (but not better that finger counting at 1 meter).
In early stages, however, the near vision may sometimes improve (the phenomenon of Second Sight).
3. Diurnal Variation of Vision: In central (cupuliform) cataract the vision is worse in bright light of the noon (day-blindness or hemerelopia) but improves as the sun sets. Whereas in peripheral cortical cataract (cuneiform) the reverse is true i.e. vision is better in bright light than dim light.
4. Distortion: Cataract may make straight edges appear wavy or curved (Metamorphopsia).
5. Colored Halos: Ring of colors of rainbow may be seen around point source of bright light. Since colored halos are important symptom of glaucoma therefore, they have to be differentiated. This can be done easily by Finchamís Test in which a vertical slit in a black disc (Staenopic Slit) is passed across patientís eye while he gazes at a point source of bright light. Colored halos caused by cataract (lenticular) seem to break into a moving fan but not that caused by glaucoma (corneal) which only become slightly dim. Moreover, the VIBGYOR of the rainbow is within outwards in lenticular halos and without inwards in corneal halos.
6. Diplopia / Polyopia: Multiple images of one object may form on the retina due to irregular refraction from the cataractous lens giving rise to Monocular Diplopia or Polyopia. This can be differentiated from binocular diplopia by cover-test and pin-hole test. Binocular diplopia disappears on covering any of the eye. Monocular diplopia does not disappear if the other eye is covered, however, it disappears if a pin-hole is placed in front of this eye.
7. Altered Color Perception: The yellowing of lens nucleus is steadily progressive leading to change in color saturation of the image seen. The artists with cataract may render their paintings browner or yellower than real.
8. Black Spots: Patient may complaint of seeing black spots fixed in his field of vision. This is unlike black spots seen in vitreo-retinal disorders, which seem to move around as floaters (muscae volitantes).
9. Behavioral Changes: Seen especially in children with cataract, who can not verbalize their complaints. Stumbling over objects, poor performance in school, loss of interest in surroundings, etc. can be some of the changes that may draw parents attention towards childís visual handicap.

Signs

1. Visual Acuity: Vision is diminished proportionate to the degree of cataract (immature from 6/9 to finger counting close to face; mature perception of light or hand movements). However, vision recorded in dimly lit room may not sometimes give true estimate of the patientís disability especially in small central opacities.
2. Leukocoria: ďWhite pupilĒ, infact the pupil appears grayish white in immature, pearly white in mature and milky white in hypermature stages of cataract.
3. Anterior Chamber: Depth of anterior chamber is normal except in intumescent cataract where it is shallow, and hypermature shrunken cataract where it is deep. It may contain cells and flare in case if lens induced uveitis.
4. Cornea & Conjunctiva: These are usually normal. Cornea may become hazy due to edema if the IOP is increased by lens induced glaucoma. Conjunctiva may be congested in lens induced glaucoma or uveitis, or if there is associated infection.
5. Iris Shadow: In immature cataract a crescentic shadow of the iris is seen in the pupil on oblique illumination. In mature cataract iris shadow is not visible as the opacity extends right to the anterior capsule.
6. Distant Direct Ophthalmoscopy (DDO): Viewing the dilated pupil using an ophthalmoscope from a distance of 25 cm reveals the cataract as black patches against the background of red glow from the fundus. This is very helpful in differentiating early immature cataract from nuclear sclerosis. Although the lens appears grayish white in both these conditions but on DDO cataract shows up as black patches but clear red glow is seen in nuclear sclerosis. Also, in mature cataract no red glow is seen as the lens becomes completely opaque.
7. Fundus: In early stages of cataract the retina may be seen by ophthalmoscopy and appear normal. It may appear deep red in color in nuclear cataract. In advanced cataract the retina cannot be seen.
8. Intraocular Pressure: IOP is normal in cataract unless lens induced glaucoma (phacolytic or phacomorphic) develops. It may be low in lens induced uveitis.
9. Purkinje-Sanson Images: All optical interfaces (junction of media to different refractive index) of the eye not only refract the light but also reflect it forming images (Catoptric) which the observer can see. Purkinje (pronounced as pur kineí) described 4 such images (or reflections) arising from anterior and posterior surfaces (1 & 2) of cornea, and from anterior and posterior surfaces of the lens (3 & 4). To this Sanson added 2 more images arising from anterior and posterior surfaces of the nucleus (5 & 6). So using a point source of bright illumination and with subjectís pupil dilated one can observe 6 reflected (catoptric) Purkinje-Sanson images from the eye.
In immature cataract the 4th image arising from the posterior surface of lens disappears and in mature cataract 4th, 5th and 6th images disappear.
10. Other Signs: Signs of aging may be observed along with cataract and are just co-incidental e.g., arcus senilis, skin laxity (dermatochalasis), senile entropion or ectropion, senile ptosis, age related macular degeneration (ARMD), grayish white granular material on lens surface or iris in pseudoexfoliation, scrolls of split layers of anterior capsule (exfoliation), tremulous lens (Phacodonesis) if the zonules are very lax or broken, dry eye syndrome, etc.

Differentiating Various Stages of Cataract

Features


Immature


Mature


Hypermature

Vision


6/9 - FC


HM - PL


HM Ė FC

Anterior Chamber


Normal (shallow in intumescent)


Normal (shallow in intumescent)


Normal to deep

Color of Lens


Grayish white


Pearly white


Milky white (with brown crescent of nucleus) or chalky white

Iris shadow


Seen


Not seen


Not seen

Distant Direct Ophthalmoscopy


Black patches against red glow


No red glow seen


No red glow seen

Purkinje-Sanson Images


4th image not seen


4, 5 & 6th images not seen


4, 5 & 6th images not seen
Complications of Cataract
I. I. Lens Induced Glaucoma

Cataract in give rise to secondary glaucoma in any of 3 ways:

1. Phacomorphic Glaucoma: Lens may swell up by absorbing fluid resulting in shallow anterior chamber. The angle may close blocking the trabecular meshwork and IOP rises. A type of secondary angle closure glaucoma.
2. Phacolytic Glaucoma: In hypermature stage the lens proteins leak out into the anterior chamber and are engulfed by macrophages. These swollen macrophages clog the trabecular meshwork leading to increase in IOP. A type of secondary open angle glaucoma.
3. Phacotopic Glaucoma: Hypermature lens may dislocate and can give rise to increase in IOP by physically blocking the pupil or angle, or displacing the vitreous which causes the block.

II. II. Lens Induced Uveitis

Lens proteins are sequestered antigens i.e. not exposed to the bodyís immune mechanisms during development. When these leak into the anterior chamber they are treated as foreign, inciting immune reaction. This results in anterior uveitis (inflammation involving iris and ciliary body). This is characterized by ciliary congestion and cells and flare in the aqueous.
III. III. Subluxation or Dislocation of Lens

In stage of hypermaturity the zonules of the lens may weaken and break. This leads to subluxation of the lens (when at least some zonules are still intact and a part of the lens still lies in the patellar fossa) or dislocation (when all zonules have broken and no part of the lens lies in the patellar fosssa.
Investigation

It involves further evaluation of the eye and general condition of the patient with regards to the feasibility and prognosis of surgical management of cataract.

1. Pupillary Reflexes: Special emphasis is placed on examining the pupillary signs as they may reveal presence of any visual pathway (afferent) or 3rd nerve (efferent) disorder. This may affect the final visual outcome e.g., afferent pupillary defect caused by optic atrophy may prognosticate poor visual result.
Special care should be taken to look for presence of Marcus-Gunn Pupil in which although both direct and consensual reflexes are present in both the eyes and pupils appear to be normal, yet on doing swinging flash light test (i.e. rapidly shifting light from one eye to the other and back) one pupil seems to dilate in response to light whereas the other constricts. This denotes presence of a relative afferent pupillary defect (RAPD) in the eye whose pupil seems to dilate. Note that the defect is partial and unequal in the two eyes.
2. Intraocular Pressure: Presence of lens induced glaucoma or co-existent primary glaucoma should always be looked for because increased IOP seriously affect the course and result of surgery. The IOP has to be well under control before the surgery for cataract is under-taken because not only high pressure increases the risk of intra-operative complications (viz. Vitreous loss, expulsive hemorrhage, etc.) but also there is a high risk of loosing vision (or visual field) postoperatively as the IOP tends to rise to high level about 2 hours after cataract operation even in an otherwise normal eye.
3. Fundus Examination: Detailed retina examination to rule out any pathology in the posterior segment (behind the lens) which may compromise visual outcome.
4. Lacrimal Syringing: It is important to rule out any block or focus of infection in the lacrimal drainage system by doing syringing. Focus of infection around the eye or even elsewhere in the body (e.g. teeth, chest, urinary tract, etc.) increase the risk of postoperative intraocular infection or Endophthalmitis which can be devastating for vision.
5. Blood Pressure: Hypertension not only leads to development of hypertensive retinopathy but also increases the chances of expulsive hemorrhage during surgery. In expulsive hemorrhage choroidal blood vessels rupture leading to bleeding between choroid and scleral, which pushes the choroid inwards and, if severe, expelling the contents of the globe.
Hypertension must be well under control in the peri-operative period and the use of phenylepherine or adrenalin should be avoided. Anti-hypertensives must be added to the preoperative medication.
6. Blood Sugar: Diabetes must be ruled out, and if present must be controlled before surgery. Diabetes can adversely affect any part of the eye especially the retina (diabetic retinopathy), wound healing is impaired and the risk of infection is extremely high. Blood sugar should be carefully monitored and kept in strict control in the peri-operative period.
On the day of operation, however, the anti-diabetics (hypoglycemics) are omitted to avoid the chance of severe hypoglycemia, and are resumed from the first postoperative day.
7. General Investigation: General body check-up and some investigations like hemoglobin, blood sugar, urine examination, ECG and X-ray Chest (where required) should be done to rule out any significant systemic disorder. If any disease is detected patient should be referred to concerned specialist for appropriate treatment.
8. Macular Function Tests: These are done to preoperatively assess the postoperative visual outcome (potential vision) based on which a prognosis is given to the patient. These tests are:

With clear media



Visual Acuity: as tested by Snellenís charts, if disproportionately less than what can be explained by the degree of cataract points to possibility of macular dysfunction.



Color Vision: Color appreciation and discrimination is best at macula because of aggregation of cones. It can be deranged in any macular pathology.



Photostress Test: Visual acuity of patient is determined and then his macula is dazzled by bright light of a 3.5 Volt Ophthalmoscope. Then the time it takes for his visual acuity to return to initial level is noted. Normal is 52 seconds but if it takes longer macular function is abnormal.



Haidinger Brushes: Using an instrument called Synoptophore a rotating beam of plane polarized blue light is shown to the patient. An image of rotating blue brushes is seen if the macula is healthy because of typical radial distribution of nerve fibers at the macula.



Potential Acuity Meter (PAM) or Visometer: Using this device reduced Snellenís Chart is projected onto patientís macula through the clear area in his lens. The smallest line that patient reads gives patientís potential vision. This test correlates the best with final postoperative visual acuity of the patient.
With opaque media



Two Point Discrimination Test: A cardboard with 2 pinholes 2 mm apart is placed 2 cm from patientís eye and a light is shone 2 feet behind it. If patient reports seeing two lights then his macula is probably normal.



Maddox Rod Test: Maddox Rod is a set of small high power red cylindrical lenses placed close to each other (or grooves cut in a red glass). A point source of white light seen through it appears as a red line. If macula is deranged the line would appear distorted, irregular, broken or would just not be seen.



Entoptic View: Rubbing a lighted bare bulb of a torch pressed over closed eyelids makes individualís own retinal (macular) blood vessels visible as dark red branches of a tree against an orange background. In macular pathology the vessels are either not seen or black patches are seen scattered with the vessels. This test should first be done on the normal eye to demonstrate to patient what he is expected to observe.



Laser Interferometry: Two beams of plane polarized light are projected on to patientís pupil. These beams undergo interference and form interference fringes of light and dark bands behind patientís lens. Then the width of these fringes is reduced and the narrowest fringes seen by the patient are indicative of his visual potential.



Visually Evoked Response (VER): Stimulation of retina by light pattern leads to suppression of alpha-wave of the EEG recorded from the occipital cortex. The smallest pattern stimulus which generates this response denotes the potential vision of the patient. Other electrophysiological tests can also be used to assess the function of the macula especially Electroretinogram (ERG) with focal foveal stimulation.

1. 9. Ultrasonography (USG B-Scan): If the cataract is advanced then the retina cannot be visualized by ophthalmoscopy, therefore, ultrasound (B-scan) is used to detect any structural abnormalities.

2. 10. Intraocular Lens Power Calculation: The power of the intraocular lens to be implanted has to be calculated for each individual. Three parameters are required as follows:



Keratometry (K): gives the refractive power of the cornea (in diopters), using an instrument called Keratometer.



Biometry or Axial Length of Globe (L): The distance (in mm) from the apex of cornea to the posterior pole of the eye is measured by a special ultrasound the A-Scan Biometer.



A Constant (A): It is supplied by the IOL manufacturer and itís value depend on the design of the lens and itís intended location in the eye (anterior or posterior chambers).

These values are put in a formula (SRK Formula) to get the power of the lens to be implanted:
IOL Power = A Ė 2.5L Ė 0.9 K

This would make the patient emmetropic. However, in some cases it is desirable to deliberatively induce a preplanned refractive error postoperatively e.g. when the other eye has a high refractive error then the planned refractive error in eye to be operated should be within + 2.5 dioptre of the other eye, in order to avoid anisometropia (unequal refrctive error) and aniseikonia (unequal image size).

Indications for Cataract Surgery

Classified in 3 groups:
I. I. Optical indications

Whenever the vision of the patient is diminished to an extent that it interferes with his normal daily life, the cataract can be operated. There is no sharp cut-off level of visual acuity below which cataract should be operated rather the decision about timing of surgery is subjective to the patientís own visual requirement. A word of caution here is that in mild diminution of vision e.g. 6/12, patient should be informed about the disadvantage of loss of accommodation that results from cataract surgery, which may offset the advantage of gain of 2-3 lines in visual acuity. Glare is another optical indication especially in individuals involved in night driving.
II. II. Medical Indications

In following conditions cataract needs to be removed urgently even if patient is not interested in visual gain or the visual prognosis is not favorable:



Hypermature cataract



Lens induced glaucoma



Lens induced uveitis



Dislocated / subluxated lens



Intra-lenticular foreign body



Diabetic Retinopathy to give Laser photocoagulation



Retinal Detachment or any other posterior segment pathology, the dignosis or treatment of which is being hindered by opacity of the lens.
III. III. Cosmetic Indication

If the vision is permanently lost because of some retinal or optic nerve pathology e.g. optic atrophy, but the white pupil caused by cataract is cosmetically unacceptable to a young patient, cataract surgery is indicated just make the pupil appear black even though is known that the vision will not recover.



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