Ординатура / Офтальмология / Английские материалы / Pediatric Opthalmology_Mukherjee_2005

10.The children may have other ocular deformity like microphthalmos, microcornea or nanophthalmos.

Signs :

1.Similar to low grade of myopia, an eye with low hypermetropia looks as normal as emmetropic eye. An eye with moderate to high hypermetropia is typically a small eye not only in anterio posterior diameter but in all directions.3

The cornea is smaller than emmetropia and the anterior chamber is shallower. The pupil is also small. In case of pathological hypermetropia coloboma of uvea is not an uncommon finding.

2.The face of the child on close inspection may not be symmetrical. Hypermetropia is generally more on the asymmetrical side and is associated with astigmatism.

3.Pseudo divergent squint. This is due to large positive angle alpha. (kappa)

4.Esotropia. This is due to high hypermetropia i.e. between +4D to +7D. And mostly is an accommodative esotropia.

5.Fundus. Overall size of the fundus is smaller than the emmetropic eye with small disc, which resembles optic neuritis without visual symptoms. This is called pseudo neuritis.

Generally fundus background has a peculiar sheen that is called shot silk appear-

ance.

The blood vessels reflect more light than emmetropia. The macula is generally situated away from the disc.

Management of hypermetropia. Management of hypermetropia like myopia is optical or surgical. Surgical treatment is not indicated in children. Optical treatment consists of prescription of spectacles or contact lens, which depend on available accommodation. There is no rule of thumb according to which power of the lenses can be determined. A rough method is -

1. Children below six years. Some accommodation for distance is physiological at this age and the child may not be aware of presence of hypermetropia. These children are asymptomatic and need no treatment. If there is a family history of hypermetropia, these children should be refracted under cycloplegia.

Treatment is called for if there is evidence of asthenopia or muscle imbalance.

2.In school going children. Who requires prolonged near work, require correction even of smaller degree.

3.Children with accommodative squint and diminished vision should be corrected. If the error of refraction is more than +3D, the child should be given glasses for constant use. Glasses less than +3D may be worn for near work only.

In children under six years, the power of glasses should be +1.5D to +2.0D less than the objective finding.

In children above six years, full correction with good vision should be prescribed.

As the child grows, some of axial hypermetropia gets reduced and the refraction may swing towards emmetropia. In rarer instances the accommodation may worsen with corresponding increase of hypermetropia in children in second decade. Keeping in mind the above factors, all hypermetropic children should get yearly ophthalmic check and undergo corresponding adjustment.

Contact lenses in hypermetropia. In principle contact lenses can correct any type of hypermetropia. It is better to prescribe contact lenses in hypermetropic children after hypermetropia has stabilised. Other indications are anisometropia and uniocular hypermetropia.

Surgical management of hypermetropia. Refractive surgery for hypermetropia are not as rewarding as in myopia. Following surgical procedures are available.

1.Hexagonal keratotomy

2.Photo refractive keratectomy

3.Lasik

4.Laser thermal keratoplasty

5.Phakic intraocular lens

Like surgical treatment of myopia, the above procedures are not indicated in children. Other types of hypermetropia seen in children are :

1.Aphakia

2.Pseudophakia

3.Over corrected myopia.

Aphakia :

—Aphakia in children is less common than seen in adults.

—Aphakia literally means absence of lens from the eye. From clinical point of view aphakia means absence of lens from pupil, complete or partial.

—Aphakia is an example of extreme form of hypermetropia where there is no accommodation. Hence aphakia is a state of absolute hypermetropia which equals total hypermetropia. Any amount of cycloplegic does not increase hypermetropia in aphakia.

Causes of aphakia in children are :

1.Congenital. This is one of the rare congenital anomalies, where either the lens vescicle has not formed (primary aphakia) or the partially formed lens has been absorbed in intrauterine life (secondary aphakia)17.

2.Trauma :

(i) Surgical. This follows surgery on congenital, developmental or traumatic cataract in children.

(ii) Accidental trauma. Spontaneous absorption of cortical matter following injury to the lens.

(iii) Traumatic extrusion of the lens from the globe, generally the lens becomes subconjunctival and forms a phacocele.

3.Displacement. This can either be congenital or may be traumatic. Sometimes the lens may be displaced in congenital glaucoma or aniridia.

Posterior dislocation is more common than anterior dislocation.

An aphakia is said to be complete when whole of lens i.e. capsule, cortex nucleus are absent from the pupillary area. It is said to be partial when a part of the pupil is devoid of the lens.

Optics of aphakia. Though aphakia is a high degree of hypermetropia, its optic differs greatly from phakic hypermetropia.

The first and foremost component of aphakia is absence of lens from optical system and equally important part is total absence of accommodation.

1.The total refractive power of the eye is reduced to +43—+44D from +60D of normal emmetropic eye with only one refractive element i.e. “cornea”.

2.The eye becomes highly hypermetropic without accommodation.

3.The anterior focal point shifts to 23.2 mm from usual 17.05 mm in front of the cornea.

4.The posterior focal point shifts to 31 mm, which is 7 mm more than the normal anterio posterior length of a normal eyeball.

5.The two principal points are almost on the anterior surface of the cornea.

6.The two nodal points almost merge with each other and are 7.75 mm behind the anterior surface of the cornea. Thus the nodal point moves forward in absence of lens.

The image is formed away from the nodal point, hence it is smaller than in emmetropic eye. The image gets magnified when aphakia is corrected by plus lenses, may be in spectacle or as contact lens. Magnification by spectacle is about 30% to 40% more than that of emmetropic eye. The corresponding magnification range between 5% to 12% in contact lens. If an IOL is put in the posterior chamber, the magnification is abolished altogether.

Symptoms of aphakia. Symptoms of aphakia consists of diminished distant vision and near vision. Uncorrected distant vision in aphakia is generally 1/60-2/60. The child can not read the usual prints in books due to total absence of accommodation.

Signs of aphakia : 1. Scar :

(a) At the limbus if a small incision lens extraction has been done.

(b) A small scar inside the limbus was a common site when needling was a popular mode of lens extraction in children.

(c) A small opacity in the cornea away from the limbus is seen in case of penetrating injury by pointed objects like needle, thorn, pin etc.

(d) An extensive corneoscleral scar is seen in corneoscleral penetrating injury.

(e) Phaco emulsification done in older children may have barely visible scar away from the limbus.

(f ) Scar is absent in blunt injury, buphthalmos, Marfan’s syndrome. 2. Anterior chamber is deeper than normal.

3.The iris is tremulous.

4.An iridectomy may be present.

5.Pupil

(a) colour :

(i) Jet black in case of posterior dislocation of lens due to any cause.

(ii) After cataract is common following needling, needling and aspiration, and spontaneous absorption of cortical matter following penetrating injury. In children posterior capsular opacification is almost universal even following micro-surgi- cal lens extraction.

(b) Position. A shifted pupil denotes incarceration of iris in the section. It is more common in accidental aphakia than in surgical aphakia.

5.Refraction. Refraction in adults shows compound hypermetropic astigmatism against the rule following conventional intracapsular or extra capsular cataract extraction. In children because the scar is very small, the refraction is generally confined to simple hypermetropia.

6.Loss of accommodation. There is total loss of accommodation.

7.Fundus examination shows small hypermetropic disc.

8.In all cases of aphakia following trauma or cases where mechanical capsulotomy has been done, the fundus should be examined by indirect ophthalmoscope for evidence of holes or traction bands.

9.Muscle imbalance and amblyopia are common in uniocular aphakia.

Management. Management of aphakia in children, in principle does not differ from adult aphakia that is to correct hypermetropia by convex lenses. Cylindrical errors should also be taken into consideration. Additional plus lenses are required for near vision.

The various options available are :

1.Spectacle

2.Contact lens

3.Intraocular lens

4.Refractive surgery.

Spectacles are suitable in bilateral aphakia in children. They are not tolerated in uniocular aphakia due to anisometropia and aniseikonia that leads to intractable diplopia and child prefers single vision without aphakic correction. This in turn leads to development of squint and amblyopia. An aphakic child may tolerate spectacle correction if the other eye has no vision, poor vision, has deep suppression or is divergent.

Even in case of binocular aphakic correction with spectacles, the child has :

1.Spherical aberration leading to pin cushion distortion. The straight lines look curved, the whole scenario consist of paraboles which keep on changing with movement of the eyes.

2.Prismatic aberration causing a roving ring scotoma between 50°–65° all round.

3.Overall restriction of peripheral field.

4.Absent or poor near vision. A child is less likely to tolerate bifocal so he requires thicker near glasses.

5.Cosmetic blemish. A child especially in teens does not like using thick heavy glasses that give an enlarged view of the eye.

6.Sliding of the spectacles on the nose. This increases the effective power of the plus lens which may help the child in near work but blur’s distant vision and increases cosmetic blemish.

Few of the advantages of spectacle correction are that they are cheap, can be replaced with ease, do not require specialised handling.

Contact lens. Contact lens correction is better option than spectacle correction especially in uniocular aphakia because :

1.Magnification by contact lens is only 5% to 10% in contrast to 30% by spectacle correction.

2.The field of vision is better, the roving scotoma is abolished.

3.Prismatic aberration is almost abolished.

4.The cosmetic blemish is eliminated.

It has been seen that small children can also tolerate contact lenses well.

Intraocular lenses are the best possible answer to aphakic correction as they are devoid of all the aberrations met with spectacle and contact lens correction. Most advantageous property being complete elimination of magnification, which by itself abolishes aniseikonia when placed in posterior chamber. Intraocular lenses are generally used as primary procedure for cataract in children but can be used as secondary procedure where the eye was left aphakic following lens extraction.

Refractive surgeries are not suitable aphakic children.

Pseudophakia. Pseudophakia is the best method of correcting aphakia. In this the lens is removed partially or totally and supplemented by an artificial lens.

The intraocular implants are made up of polymethacrylate (PAMA), silicon, acrylic or hydrogel. The first is a rigid, hard lens while the others are malleable.

The IOL can be implanted as a primary procedure i.e. removal of lens with simultaneous implantation of lens or as a secondary procedure where the lens is removed in first session and IOL implantation later.

According to position of lens, the implant can be in the :

1.Anterior chamber

2.Iris fixed

3.Posterior chamber—In the bag

In the sulcus

4. Scleral fixed.

between the two focal lines is known as focal interval that represents the astigmatic power of the eye. The aim of treatment is to abolish this distance by optical methods i.e. spectacle, contact lens or surgery so that the two focal lines merge with each other, and a pinpoint focus is formed on the retina. In between the two focal lines is the circle of least diffusion which represents the spherical power.

A perfect stigmatic eye is an exception. All eyes have some minor degree of astigmatism without any symptoms. The cornea of a new born is almost spherical18, with age slight astigmatism is natural due to pressure of the lids on the cornea. The vertical meridian is steeper hence slightly more myopic than flatter horizontal meridian, which remains emmetropic. This is known as direct astigmatism or astigmatism with the rule. In contrast to this, where horizontal curvature steeper, the condition is called indirect astigmatism or astigmatism against the rule.

2.According to axis of astigmatism

3.According to position of the image.

According to site : Corneal astigmatism is the commonest form of astigmatism both regular and irregular.

Lenticular astigmatism :

1.Decentered lens

2.Different curvature in different meridian i.e. lenticonus, subluxation, coloboma of lens.

3.Difference in refractive index i.e. early cataract.

Retinal astigmatism. This is seen generally with retrobulbar mass or oblique placement of macula.19

According to axis of image : Regular astigmatism

1.The two meridians are at right angles to each other, one of them is horizontal and the other is vertical. This is the commonest type of astigmatism.

2.The two axises are at right angles to each other but not horizontal and vertical, the condition is called oblique astigmatism. The axises are off the horizontal or vertical by 20° or more. The axis in one eye is mirror image of the other eye i.e 80° and 110° or 20° and 160°.

3.The difference between the two meridians is less than 90°, the condition is called bioblique astigmatism.

Irregular astigmatism is that astigmatism where astigmatism in the principal meridian vary. This is caused due to corneal irregularity like corneal scar, keratectasia, keratoconus, pterygium, limbal dermoid, post keratoplasty.

According to position of image in relation to retina. The astigmatism can be simple, compound or mixed.

Simple astigmatism is that astigmatism in which one meridian is emmetropic, the other is either myopic or hypermetropic. The former is called simple myopic astigmatism, while the latter is called simple hypermetropic astigmatism. Each is corrected by suitable single cylinder of appropriate sign, axis and power.

Compound astigmatism is that astigmatism where both the meridians are either myopic or hypermetropic and known as compound myopic or compound hypermetropic astigmatism respectively. They are corrected by sphere and cylinder of same sign i.e. compound myopic astigmatism is corrected by myopic sphere with myopic cylinder.

Mixed astigmatism is that astigmatism where two meridians have different signs i.e. one is myopic, the other is hypermetropic or vice-versa. In mixed astigmatism the power of the cylinder is always more than the sphere. They are most difficult to correct. They are very common following IOL implant.

Symptoms of astigmatism :

1.Small degree of astigmatism may be symptomless.

2.Diminished distant vision—As the eye fails to form a sharp image on the retina, the visual loss is considerable. However sometimes high astigmatism may not cause corresponding degree of loss of vision i.e. a child with 6/12 vision may require just 0.75 to 1.00 Dsp to bring the vision to 6/6. But an astigmatic may require as much as 2 to 2.5 Dcyl to attain same vision.

3.Difficulty in focusing near objects—As accommodation fails to correct astigmatism, the near vision is never comfortable for an astigmatic.

4.Head turning and tilting—The child may turn or tilt the head to compensate for the axis of astigmatism.

5.Narrowing of interpalpebral fissure—The child tries to produce a pinhole effect to improve the vision. This attempt is less effective than seen in spherical ametropia.

6.Muscle imbalance is more common in astigmatism than in other errors of refraction.

7.Asthenopia and asthenopia related symptoms are more common in astigmatism of low grade. They are : Watering, redness of eye, recurrent blepharitis, stye, chalazion, frontal headache.

8.Muscle imbalance.

Signs of astigmatism :

1.Externally the eyes may not look abnormal. In case of compound high myopic astigmatism the eye may look large, may similarly look small in case of compound hypermetropic astigmatism. Recurrent stye, chalazion, blepharitis, presence of haemangioma or neurofibroma on the lid should arouse suspicion of astigmatism.

2.Placido disc may show irregularity in the circles, in irregular astigmatism and crowding and elliptical shape in high regular astigmatism.

3.Computerised keratoscopy shows irregularity in the corneal surface.

4.Refraction always shows difference in refraction in two principal meridians.

5.Keratometry shows difference in power in different meridian and their axises.

6.On fundus examination the optic disc looks oval. Vertically oval disc is more common than horizontal.

7.An astigmatic child when examined on E chart may not be able to tell the direction of the arms of E. He may be able to tell the direction in vertical direction but fumble in horizontal direction and vice versa.

8.On astigmatic fan the child may see some lines clearly and not those at right angles to it.

9.Vision with pinhole does not improve satisfactorily in astigmatism. A child with -2D myope will improve to 6/6 with a pinhole but a child with -1Dcyl may improve only to 6/12.

Management

1.No treatment—If there is no visual loss or there are no symptoms of eye strain, asthenopia or muscle imbalance, no treatment is required. The child is examined once every year and his retinoscopy is done under cycloplegia.

2.Prescription of glasses :

1.Simple astigmatism is corrected by single cylinder of appropriate power and sign at proper axis.

2.Compound astigmatism is corrected by prescribing sphere and cylinder of same sign.

3.Mixed astigmatism is corrected by sphere and cylinder of opposite sign.

As a rule every attempt should be made to correct cylindrical defect fully.18

The spherical correction should be done on usual lines of spherical ametropia.

While correcting astigmatism utmost attention should be given to correct axis of the cylinder. A wrongly placed cylinder is more troublesome than without one.

In mixed astigmatism the combination that is most comfortable should be prescribed i.e. minus sphere with plus cylinder at right angles or plus cylinder with minus cylinder at horizontal axis.

The power and axis of the cylinder can be checked by :

1.Auto refraction—These are good for non-verbal children who can not be tested subjectively. However refraction under cycloplegia should get proper weightage.

2.Keratometry—This is more important in contact lens fitting than spectacle. This measure the curvature of a anterior corneal surface only 3 mm wide. It measures the astigmatism of the front surface of the cornea at two points about 1.25 mm on either centre side of the cornea.

3.Foggin

4.Astigmatic fan

The last two are not suitable for small children.

5.Jackson’s cross cylinder. This is the best and most accurate method to verify power of cylinder and axis of cylinder.

The spectacles given for astigmatism should have proper fitting otherwise the axis may change giving poor vision and discomfort.

Contact lens. Contact lenses are prescribed only when the child can manage the contact lens himself. Though small degree of regular astigmatism are well corrected by contact lens, it is better to go for spectacle correction because it is cheap, easily replaceable, and require no maintenance. Contact lenses are more suitable for high astigmatism, bi-oblique astigmatism and irregular astigmatism.

Spherical contact lenses fail to correct astigmatism more than 2 to 3 Dcyl. For high cylindrical error toric contact lenses are best suited.

A toric lens20 should have full corneal coverage and good centering. The lens should have good movement with each blink, the up and down gaze. The lens should give vision comparable to spectacle vision if not better. The toric contact lenses are difficult to fit.21, 22

Anisometropia

When the refractive power of two eyes is different, it is called anisometropia in contrast to isometropia where refraction in two eyes is equal. Small degree of anisometropia is more or less the rule. Perfect isometropia is exception like perfect emmetropia and stigmatic eye. Anisometropia is more common in astigmatism, may be congenital. A difference in refraction in two eyes results in difference in retinal size in two eyes. One diopter of difference results in 2% difference in size of image. In myopia the size is reduced while in hypermetropia the size is magnified. A difference in 2.5D between two eyes will result in 5% difference in size of image. Difference in size of two retinal images is called aniseikonia. A difference in size up to 5% between the two eyes is the limit of tolerance beyond which diplopia results.

A difference of 2.5D or more is called clinical anisometropia. Anisometropia upto 2.5D is well tolerated, of course some may not tolerate even a smaller difference. However, some individuals may tolerate difference upto 4D.

Etiology of anisometropia.Anisometropia can be congenital or acquired. Congenital anisometropia is generally hereditary and due to differential growth of two eyes.

Acquired anisometropia. Commonest cause of anisometropia is uniocular aphakia. Second cause that is being seen more often is wrong calculation of IOL power. Other such cause is over or under correction following refractive surgery and uniocular keratoplasty.

Types of anisometropia :

1. Simple —Spherical —Astigmatic

2. Compound —Spherical —Astigmatic