Aphakia (Aphakias)

Aphakia describes the absence of the eye lens. It most commonly occurs after surgery for cataract removal, but is also associated with trauma and congenital conditions.

This disorder is associated with the following process: congenital.

Presentation

Patients with aphakia can present with a range of symptoms. They generally complain about poor vision, caused either by hypermetropia or accommodation loss. Hypermetropia is also called long sightedness and is associated with a +4 visual acuity. Unlike the implications of the commonly used term, it requires visual correction for both near and distance vision. A loss of accommodation, on the other hand, reflects an inability to maintain focus on an object with changing distances. Patients may also report erythropsia, a condition in which visual objects appear to have a red color and cyanopsia, in which objects tend to have a blue tint. Patients also describe more intense colors. This is caused by increased entry of sunlight into the eye because of the absence of the lens. Red and blue wavelengths are normally absorbed by the lens. When this does not occur, they reach the retina and influence visual perception. 

Other signs and symptoms include a scar around the iris in cases of aphakia caused by surgery, a jet black pupil, a fundus that is small and hypermetropic on a fundus exam, iridodonesis (a tremolous iris because of a lack of support from the lens) and an absence of 3rd and 4th purkinje images.

Workup

A comprehensive eye exam is essential in the workup of aphakia. The cornea, anterior chamber, fundus and iris need to be examined. In addition, eye pressure should be measured and visual acuity should be assessed. Ophthalmologists can also determine distance, refraction and near vision.

Signs on physical exam that are particular to aphakia include a limbal ring scar. The latter corresponds to a black ring that encircles the iris and that will only manifest in patients who have undergone eye surgery. Another distinctive sign is iridodonesis, which describes the jittering of the iris because of absent support from the lens. Finally, the eye exam will show a small, hypermetropic fundus. The fundus corresponds to the interior surface of the eye. Hypermetropic describes an eye ball that is short. In this case, light cannot be focused on the retina but falls behind it.

Treatment

Treatment of aphakia consists of glasses, contacts or surgery.

Glasses are used only if both eyes are affected. They are characterized by several drawbacks including a decrease in the field of vision and the need for higher magnification. In addition, because of the thick lens appearance, they are considered aesthetically displeasing.

Treatment for infants and babies consists mostly of lenses. Lenses are designed to be safe for babies to sleep in and can be used for a relatively longer duration than common lenses. It is also advisable to use eye drops and an eye patch. This encourages the infant to employ the eye affected with aphakia. Treatment is critical in infants to prevent the development of ambylopia.

The American Association for Pediatric Ophthalmology and Strabismus recommends early surgical or optical treatment for babies and infants with cataracts. Subsequently to the removal of cataracts, parents have the choice to pick between several treatment modalities such as aphakic glasses alone, aphakic contact lenses with bifocal glasses or intraocular lenses with bifocal glasses. In general, perfect optical correction can be provided by aphakic contact lenses.

On the other hand, surgical treatment in addition to intraocular lens implantation is the treatment of choice for adults. During intraocular lens implantation, the surgeon places a synthetic lens within the eye. The procedure is associated with a relatively low number of complications and has excellent outcomes. Most patients report excellent visual improvements.

Placement of an intraocular lens in children is associated with significant problems related to the eyes and the visual system overall. The appropriate timing of the procedure in children is still controversial. Complications may be possible at any age. Bifocal glasses may be additionally required for children who have undergone intraocular lens implantation or those who wear high power contact lenses. They can help in improving both near and distance vision.

Intraocular lenses are the treatment of choice for aphakic older children and are now more commonly used among infants and young children [5] [6]. Current studies are not sufficient to determine long term results when the procedure is performed in infancy [7] [8]. Some case series suggest that visual outcomes are better when unilateral intraocular lenses are placed in infancy in comparison to contact lenses. Nonetheless, postoperative complications are still significant and it is not clear if benefits outweigh the risks [9] [10] [11].

Contact lenses are still the best treatment modality in young infants, even though their effectiveness can be limited by several problems [12]. Infants usually do not display the necessary cooperation during placement and removal of the lenses. They are also relatively expensive and can be easily lost. Because children tend to have steep corneas, they may also not easily fit. Medical complications such as bacterial keratitis can also occur [13] [14] [15]. All of these potential problems play a significant role in producing relatively poor outcomes among infants with unilateral aphakia.

Prognosis

Aphakia generally has a good prognosis if no severe complications take place. It is important to correct vision during childhood. Because of the rapid change of the size of the eyes and the range of refractive errors, it may be necessary to perform frequent adjustments. In case vision adjustment is not properly followed up in children, permanent loss of vision may take place.

Etiology

There are three main etiological factors causing aphakia. Genetic defects can either be primary or secondary. Primary congenital aphakia is associated with a severe malformation of the eye, whereas secondary aphakia is a less severe form. Both primary and secondary congenital aphakia have been linked with FOXE3 mutations [2].

Aphakia is also a potential complication of surgical removal of cataracts and can occur after traumatization to the eyes. The latter can result in the extrusion or dislocation of the lens. Because of the pressure on the eye, the lens is forced out of it.

Finally, aphakia can also be caused by severe inflammation of the eye.

Epidemiology

Catracts commonly occur amongst older individuals. Around 17.2% of all Americans develop cataracts after the age of 50. Aphakia takes place in approximately 5.1% of all individuals with cataracts in the United States. Numbers are projected to rise to 30.1 million Americans having cataracts in 2020, with 9.5 million Americans expected to be diagnosed with pseudiphakia or aphakia [3]. 

A review study on 521 Danish patients who underwent surgical extraction of cataracts with a follow up period of 39 months found that aphakic retinal detachment occurs in 1.3% of cases. 1% of all affected suffered no surgical complications and 5.4% were myopic. Statistical analyses reveal that an age below 70 and myopia are statistically associated with the development of aphakia after cataract removal. This indicates that myopic patients who undergo cataract removal at an early age are the highest risk population. Among all cases, 128 patients passed away. The mortality rate is not more elevated than that of the general population. This suggests that cataracts in old age are not associated with systemic diseases that increase mortality, but rather reflect localized eye disease [4].

Sex distribution
Age distribution

Pathophysiology

Congenital primary aphakia is characterized by a complete absence of a lens. It is associated with other ocular abnormalities such as microphthalmia (small eyes), sclerocornea, dysplasia of the retina, absence of the iris, aplasia or dysplasia of the anterior chamber of the eye.

Congenital primary alphakia is characterized by an arrest of early development during the 4th or 5th week of embryogenesis. There is an absence of the lens structure and an association with mutations of the FOXE3 genes.

On pathohistological analyses, primary congenital aphakia involves a complete absence of the lens. There is an underlying lack of induction for the surface ectoderm and a possible mutation in the PAX6 gene. In addition, severe systemic or ocular developmental abnormalities are generally present. In contrast, histological characteristics of secondary congenital primary aphakia depend on the underlying cause. A lens usually develops but it is extruded before or during the process of birth. Secondary congenital aphakia is associated with prenatal infections, for example with the rubella virus.

Prevention

There are no current preventive measures for aphakia.

Summary

Aphakia refers to the absence of the lens in the eye. There are three main causes behind aphakia in humans. The condition can either be a result of congenital causes, surgery for the treatment of cataracts or severe inflammation. Congenital aphakia can be primary or secondary. In primary congenital aphakia, there is a complete absence of lens development due to a developmental insult in the 4th or 5th week in embryogenesis. The condition tends to be associated with severe ocular and systemic abnormalities and is linked to mutations in the FOX3 and PAX6 genes. Secondary congenital aphakia is a relatively milder form of the disease and is not necessarily associated with secondary developmental disturbances. It is usually caused by congenital infections, particularly with the rubella virusCataract surgery is the most common cause of aphakia. Aphakia occurs in around 5% of all patients who require cataract surgery. Around 17% of all Americans older than 50 will develop cataract and undergo surgery. 

Patients with aphakia present with small pupils and visual abnormalities that are mostly due to a loss of accommodation and hypermetropia [1]. They also tend to develop erythropia and cyanopsia, in which objects acquire reddish and bluish hues respectively. This is because, in the absence of a lens, more light in the red and blue range is absorbed by the retina. A limbal scar is a specific sign for aphakia that follows cataract surgery.

Diagnosis is established after an extensive exam of the eye and treatment depends on the age of the patient. Young infants generally wear special contact lenses whereas adults require intraocular lens transplantation. Glasses are also another option, although they may be cosmetically troublesome because of the necessity of thick lenses. Prognosis is good in the absence of complications. It is also critical to correct vision during childhood to avoid the development of strabismus.

Patient Information

Aphakia is a medical condition characterized by the absence of the lens. It can be caused by a congenital disease that occurs before birth, a surgery to remove cataracts, trauma or because of a severe inflammation affecting the eye. Congenital aphakia can either be primary or secondary. Primary congenital aphakia is due to a developmental abnormality that occurs during pregnancy and results in a complete absence of the lens. It is caused by genetic mutations in the FOXE3 and PAX6 genes. In secondary congenital aphakia, the lens usually develops but is then forced out of the eye during or before birth. It is most commonly caused by infections that take place while the fetus is still in the womb. Surgical treatment of cataracts is the most common cause of aphakia.

Patients with aphakia usually present with abnormalities in vision. For example, they are unable to focus on moving targets or they have problems with visual acuity for both close or far objects. They also tend to see visual objects with a reddish or a bluish hue. This is because in the absence of a lens, more sunlight enters the eye and falls on the retina, the organ responsible for the transmission of light signal to the brain. 

Treatment consists of either glasses, contact lenses or lens transplantation. The latter is the preferred treatment in adults, whereas contact lenses are used in infants. Prognosis is very good when no complications occur. It is very important to correct vision in childhood to avoid the development of strabismus.

Self-assessment

References

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  4. Naeser K, Kobayasgi C. Epidemiology of aphakic retinal detachment following intracapsular cataract extraction: a follow-up study with analysis of risk factors. J Cataract Refract Surg. 1988 May;14(3):303-8.
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  14. Neumann D, Weissman BA, Isenberg SJ, Rosenbaum AL, Bateman JB. The effectiveness of daily wear contact lenses for the correction of infantile aphakia. Arch Ophthalmol. 1993 Jul;111(7):927–930. 
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