Index
It is a condition that involves not having an eye lens, due to surgical removal, a perforating wound or ulcer, or a congenital anomaly.
The lens of your eye is a clear, flexible structure that allows your eye to focus. This condition is more common in adults with cataracts , but it can also affect babies and children.
It causes loss of accommodation, hyperopia and deep anterior chamber. Complications include retinal or vitreous detachment and glaucoma .
Babies are rarely born with aphakia. Most of the time, the occurrence is the result of surgery to remove a congenital cataract (clouding of the lens of the eye, which can prevent light from entering the eye and focusing clearly).
Congenital cataracts usually develop as a result of infection of the fetus or genetic reasons. It is often difficult to identify the exact cause of these cataracts, especially if only one eye is affected.
People with aphakia have relatively small pupils and their pupils dilate to a lesser degree.
Symptoms of aphakia
Without the focusing power of the lens, the eye becomes very visionary. This can be corrected by wearing glasses, contact lenses, or by implanting an artificial lens.
The main symptom of aphakia is not having a lens. This can lead to other symptoms, such as:
- Blurry vision.
- Trouble focusing on objects.
- Changes in color vision, which involves colors that appear faded.
- Trouble focusing on an object as its distance changes.
- Hypervision, or difficulty seeing things up close.
Artificial lenses are described as “pseudophakic.” Furthermore, since the lens is responsible for adjusting the focus of vision to different lengths, patients with aphakia have a total loss of accommodation.
Some people have said that they perceive ultraviolet light, invisible to those with glasses, such as whitish blue or whitish violet. Miotics are effective in aphakic glaucoma.
What causes aphakia?
waterfalls
Cataracts can make your eyes look milky and cause cloudy vision. They are caused by proteins clumping together on the lens, which tends to occur with age.
This makes it more difficult for your lens to refract light on the retina, resulting in cloudy vision. Cataracts are very common, affecting about 24.4 million Americans age 40 and older, according to the American Academy of Ophthalmology.
In rare cases, babies are born with cataracts. This is usually due to genetics or exposure to certain diseases, such as chickenpox.
Talk to your doctor if you or your baby have cataract symptoms so they can rule out any other eye problems.
Genetics
Some babies are born without eyeglasses. This category of aphakia has two types, called congenital primary aphakia and secondary congenital aphakia.
Babies with primary congenital aphakia are born without glasses, usually due to developmental problems or a genetic mutation.
Babies with secondary congenital aphakia have a lens, but it is absorbed or separated before or during birth. This type of aphakia is also associated with exposure to a virus, such as congenital rubella.
Injuries
Accidents and injuries to your face can damage your lens or cause it to come off inside your eye.
How is aphakia diagnosed?
Usually, Afaquia is diagnosed with a standard ophthalmic exam. Your doctor can also examine your iris, cornea, and retina.
How is aphakia treated?
Treatment of aphakia generally involves surgery for both children and adults.
It is important for babies with aphakia to have surgery as soon as possible because their eyes develop very quickly.
The American Academy of Pediatrics recommends that infants with aphakia receive surgery when they are about a month old.
They will need special glasses or contact lenses that they can sleep in and wear for long periods of time after surgery. They can receive an artificial lens implant once they are about a year old.
Surgery for adults with aphakia often involves removing the damaged lens if necessary and implanting an artificial one. The procedure, usually performed under local anesthesia, can take less than an hour.
Your doctor may prescribe contact lenses or glasses after surgery to improve your vision.
Does the aphakia cause any complications?
Most people recover easily from eye surgery, but there are some possible complications.
Aphakic glaucoma
Having any type of eye surgery can increase your risk of developing glaucoma. This happens when pressure inside the eye damages the optic nerve. If left untreated, glaucoma can lead to vision loss.
After having any type of eye surgery, be sure to follow up with regular eye exams for glaucoma.
Retinal detachment
People who have had eye injuries or surgery are also at higher risk of developing a detached retina. The retina has visual receptors that change images into electrical impulses, which are sent to the brain.
Sometimes the retina detaches and becomes separated from the tissue that holds it in place. Symptoms of a detached retina include:
- See spots or flashes of light.
- Loss of peripheral (side) vision.
- Daltonismo.
- Blurry vision.
Get immediate medical treatment if you think you have a detached retina, as it can lead to total blindness without prompt treatment.
Vitreous detachment
Vitreous humor is a gel-like substance that fills the inside of your eye and attaches itself to the retina. Both aging and eye surgery can cause changes in the vitreous humor. These changes can cause it to separate from the retina, resulting in a vitreous detachment.
A vitreous detachment usually doesn’t cause any problems. However, sometimes the vitreous humor pulls so hard on the retina that it creates a hole or even retinal detachment.
Symptoms of vitreous detachment include seeing:
- Cobweb spots in your vision.
- Flashes of light in your peripheral vision.
If you have a vitreous detachment, work with your doctor to make sure it isn’t causing any additional problems.
Optical correction of aphakia in children
For several reasons, the correction of aphakia differs between children and adults. First, a child’s eye continues to grow during the first years of life and early childhood.
The refractive elements of the eye undergo radical changes; Axial elongation and changes in corneal curvature are the main factors influencing refractive changes in early childhood.
For example, the average corneal curvature flattens from 52D at birth to 43.5D at the age of 18 months.
Furthermore, the axial length (LA) increases from an average of 16.8 mm at birth to 23.6 mm in adulthood. The second problem is that the immature visual system in young children puts them at risk for amblyopia if the visual input is out of focus or is uneven between the two eyes.
Third, certain complications, which may be acceptable in adults, are unacceptable in children.
Over the last decade, the optical correction of aphakia in children has improved dramatically; however, for obvious reasons, precise optical rehabilitation and postoperative supervision in these cases is more difficult than in adults.
Optical rehabilitation in pediatric aphakic patients remains a challenge for ophthalmologists.
External optical correction
An aphakic eye, especially in children, has optical properties that are different from normal phakic eyes.
Currently, optical correction of aphakia in children includes aphakic glasses, aphakic contact lenses (AC), and the implantation of primary or secondary intraocular lenses, each with their own specific advantages and disadvantages.
Afakic glasses
Aphakic glasses are rarely used for the correction of binocular or monocular aphakia in children.
Restrictions on the use of aphakic glasses are poor optics; These include narrowing of the visual field to approximately 30º, an increase in the amplitude of the nystagmus, and a marked disparity in the size of the retinal image of approximately 30%.
Also, anisometropy exceeding 3D in spherical error or 1.5D in cylinder error makes glasses a wrong choice.
Anisometropia produces confusion that can lead to permanent suppression, amblyopia, or abnormal correspondence of the retina and the development of concomitant strabismus.
Spectacle lenses in unilateral aphakia represent a barrier to binocular vision leading to amblyopia. Another disadvantage of wearing glasses in newborns and babies is their added weight and size.
The shows are cosmetically, visually and psychologically undesirable. Correction of aphakia with aphakic glasses is justified in rare cases or in the absence of parental cooperation.
Aphakic contact lenses
Contact lenses can be fitted to the eyes of all age groups and are a highly effective device in the visual rehabilitation of pediatric aphakia.
The most common reasons for pediatric contact lens fitting are unilateral or bilateral aphakia; in unilateral cases they can be applied as primary treatment in association with the normal eye obturation.
Many bilateral aphakic subjects apply contact lenses with more additional power for near vision correction in infancy, switching to bifocals when they are young.
Long-wear soft or rigid lenses are generally well tolerated, although frequent power changes and lost lenses are significant financial barriers for many families.
Three types of contact lenses are used for pediatric aphakia: rigid gas permeable (RGP) lenses, silicone elastomers, and hydrogels.
Silicone elastomer lenses are highly permeable to oxygen, even more so than rigid gas permeable lenses.
Due to the physical properties of silicone elastomer, lipid and mucin deposits easily accumulate on the surface of such lenses, causing complications to the cornea and conjunctiva, so such lenses should be worn only during waking hours. .
Hydrogel lenses, in principle, should be used in children over 4 years of age. These lenses are commercially manufactured in selected parameters, which are considered a disadvantage with the small eyeballs and steep corneas of newborns and babies.
In pediatric aphakia, higher power lenses have a thick central part that inherently reduces oxygen permeability and causes various corneal and conjunctival complications such as:
- Conjunctivitis, giant papillary conjunctivitis, neovascularization, corneal edema, abrasions, infectious keratitis, endothelial polymethism and acute red eye reactions.
Such lenses can damage the small developing balloon. However, its only advantage is the low cost. This type of lens is used only in exceptional cases.
Rigid gas permeable lenses may be one of the best options for treating pediatric aphakia. Today, most doctors apply this type of contact lens.
Special fitting considerations are required for eyes with microphthalmia after congenital cataract surgery that have pronounced corneas and mild postoperative astigmatism.
Due to the small diameter of the cornea, a narrow eyelid cleft with tight lids, rigid gas permeable lenses are a good choice.
Compared to other types of contact lenses, rigid gas permeable lenses are the healthiest lenses for young developing eyes. It requires simple daily care that is of great convenience to parents.
However, the main problems with contact lens wear are poor compliance with long-term wear, lens loss, and eye irritation and infection.
Lentes intraoculares
Intraocular lens implantation in children provides the benefit of reduced compliance dependency compared to other external optical devices (aphakic glasses and contact lenses) that provide at least partial correction.
These are important advantages for visual development in eyes prone to amblyopia.
However, concerns about primary implantation of intraocular lenses are technical difficulties in implanting an intraocular lens in children’s eyes, selecting an appropriate intraocular lens, and the risk of visual axis opacification (OEV) or posterior capsular opacification (PCO). after implantation.
Despite primary posterior capsulectomy and vitrectomy, the visual axis opacification rate is higher in pseudophakic infant eyes than in aphakic infant eyes.
On the other hand, although it is possible for an eye with a unilateral infantile cataract to achieve good vision after contact lens correction, such a result is an exception rather than a rule.
Both intraocular lenses and aphakic contact lenses can provide similar visual acuity (VA) after surgery for unilateral cataract in the presence of good compliance with contact lens wear.
However, intraocular lenses provide better visual acuity when compliance with contact lens wear is moderate or poor. For bilateral aphakia, glasses and / or contact lenses may be a reasonable option.
As for unilateral cataracts in childhood, the question of when to implant an intraocular lens is not resolved. The results of ongoing multicenter clinical trials are likely to guide us in the near future.
For children beyond infancy, intraocular lens implantation is less controversial.
Parental counseling
Cataract surgery in children is only one step on the long road to visual rehabilitation, not the end. Parents / caregivers play a crucial role in the postoperative care of the eye and the treatment of amblyopia after aphakia.
They should be aware that a successful visual result depends on more than just the surgical procedure; it is also highly dependent on your ability to maintain adequate aphakic correction and continue amblyopia therapy.
Before proceeding with intraocular lens implantation, it is of great importance to discuss the main pros and cons of the available options with parents / legal guardians.
A child operated on for cataracts requires regular scheduled care in the first decade of life, and then every 1-2 years throughout life.
Therefore, to achieve the best visual result for the child, the long-term commitment of the parents is required.
Changing refraction dictates frequent follow-up exams. Glaucoma is known to develop even years after cataract surgery. The child may need serial tests under anesthesia until he is cooperative enough.
Parents should also be informed about the treatment of visual axis opacification, strabismus, glaucoma, and rarely, off-center IOL, syneiolysis, or removal of a loose stitch.
For eyes operated on during early childhood, parents should know that follow-up in the first six months is crucial.
Despite performing primary posterior capsulectomy and vitrectomy, many children’s eyes develop opacification of the visual axis, mainly within the first six postoperative months.
For eyes operated with an intact posterior capsule, parents should be informed of the requirement for a secondary procedure for posterior capsular opacification.
Parents of children with lens implants are also aware that glasses are likely still necessary postoperatively, even with intraocular lens implantation.
Also, the correction of the glasses may need to be changed frequently after surgery due to changes in refraction.
Intraocular lens implant site
Placement of the intraocular lens in the capsular bag is preferred when capsular support is adequate.
When the stability of the capsular bag is compromised, as in the case of traumatic cataracts and the zonular damage that is a common cause of unilateral aphakia in children, a capsular tension ring (CTR) can be used. English).
Fixation of the ciliary groove of the intraocular lens can also be done in the absence of a suitable capsular support for implantation in the bag. However, the incidence of uveitis and pupillary uptake is higher with sulcus fixation.
The younger the child, the greater the challenge for bag implantation of the intraocular lens, especially due to the difficulties of capsulorhexis in this age group.
Pediatric Capsulorhexis
Performing a complete manual anterior continuous curvilinear capsulorhexis and posterior continuous curvilinear capsulorhexis is a critical step to ensure safe placement of the intraocular lens within the capsular bag.
Continuous anterior and posterior curvilinear capsulorhexis can be difficult to perform due to the high elasticity of the capsule and tension in children. Capsulorhexis of the anterior capsule in young patients is more difficult than posterior continuous curvilinear capsulorhexis.
Capsular dye-assisted cataract surgery has been used to improve visibility and increase the rate of complete anterior and posterior continuous curvilinear capsulorhexis.
Saini et al. conducted a prospective randomized trial to create anterior and posterior continuous curvilinear capsulorhexis in pediatric cataract surgery with and without application of trypan blue dye.
The majority (91.3%) of the eyes had complete anterior curvilinear capsulorhexis and 82.6% had complete posterior continuous curvilinear capsulorhexis when trypan blue was used to stain the capsule.
Compared with 73.6% and 52.6% of anterior and posterior continuous curvilinear capsulorhexis, respectively, in eyes without blue trypan.
The difference was significant between the groups. Sharma et al. evaluated the efficacy of trypan blue in posterior capsulorhexis with optical capture in pediatric cataracts in a prospective randomized study.
Optical capture was possible in 17 of 18 eyes in trypan blue-assisted surgery and in 11 of 17 eyes in which no dye was used (P = 0.04).
Secondary intraocular lens implantation
The vast majority of children undergoing secondary intraocular lens implantation have had primary posterior capsulotomy and anterior vitrectomy.
If adequate peripheral capsular support is present, the intraocular lens is placed within the reopened capsular bag or in the ciliary groove.
A fully polymethylmethacrylate (PMMA) intraocular lens is ideal for sulcus placement and should be considered, especially when capsular debris is insufficient.
However, these intraocular lenses require a larger incision for implantation.
The most commonly used intraocular lens for secondary implantation is the AcrySof three-piece intraocular lens (Alcon Laboratories, Inc., Texas, USA, Model MA60AC).
It has a posterior angulation that makes it suitable for implantation of the sulcus. However, the haptics are smooth and decentration can occur, particularly in eyes with large anterior segments and axial length greater than 23 mm.
When capsular support is unsuitable for sulcus fixation in a child, implantation of an intraocular lens is not recommended unless each contact lens and eyeglass option has been fully explored.
Anterior chamber intraocular lenses and scleral or iris-fixed posterior chamber intraocular lenses are used in children when other viable options are lacking, although the long-term consequences of these placements are unknown.
Anterior chamber intraocular lenses should be of a flexible open-loop design and an appropriate size for the anterior chamber.
Sclerotic sutured intraocular lenses are usually fixed with 10-0 prolene suture, but biodegradation concerns have been raised because late intraocular lens decentrations (5-15 years after surgery) have been documented.
Fixation of the iris is also an alternative in children when there is a lack of adequate capsular support for fixation of the sulcus or bursa.
Iris fixation as in “lobster claw” style lenses (Verisyse) is used for implantation of phakic intraocular lenses in some tall myopic children.
The aphakic version of this intraocular lens is available for compassionate use, but must be ordered through the Food and Drug Administration (FDA) on a case-by-case basis.
Time for intraocular lens implantation
Despite advances in adult intraocular lens implantation, the transition to primary intraocular lens implantation in children, specifically those younger than 1 year of age, has been gradual.
Reasons for reluctance to wear intraocular lenses in young children include ocular growth, higher incidence of posterior capsular opacification, and increased reactivity of the eye.
There are several reports of intraocular lens implantation in children older than one year and, to a lesser extent, in younger children.
The trend toward intraocular lens implantation in monocular patients 6 months and older is likely to continue, with some surgeons using intraocular lenses even in younger children.
Bilateral intraocular lens implantation has been reported less frequently than unilateral cases, and most series describe children older than 2 to 3 years.
For children younger than 2 years, there are few data on bilateral intraocular lens implantation, possibly because many children who are bilateral aphakic can be treated well with aphakic glasses or contact lenses.
Challenges of Pediatric IOL Power Selection and Calculation
Calculating and selecting an “optimal” IOL power for the small eye of a growing child presents unique challenges.
The requirement to implant a fixed power lens in a growing eye makes it difficult to choose an “optimal” intraocular lens lens that provides the greatest benefits for the child’s eye.
The younger the child is at the time of surgery, the more difficult the problem. This is a challenging task for ophthalmologists in industrialized countries, and probably even more difficult for ophthalmologists in developing nations.
The lack of operating room instrumentation in many parts of the developing world, such as the handheld keratometer and A-scan ultrasound, increases the difficulty of calculating the power of the intraocular lens for pediatric cataract surgery.
Even with the availability of A-scan and automated keratometers in the operating room, calculating intraocular lens power for small children’s eyes is challenging. We also use formulas originally designed for adult eyes.
To accurately predict optimal intraocular lens power, the formulas require measurement of axial length, corneal power, and anterior chamber depth (ACD).
When using ultrasonic pulse echo techniques for biometry, errors in predicted refraction after intraocular lens implantation are attributed to faulty axial length measurement (54%), keratometric errors (38%), and errors in the estimation of the depth of the postoperative anterior chamber (8%).
Improving the accuracy of axial length determination has been suggested to have the greatest impact on improving prediction of intraocular lens power.
This is because an axial length measurement error of 0.5mm, for example, is capable of inducing a postoperative refractive error of up to 1.4D.
Two devices have been developed that use low coherence reflectometry, which is a technique similar to partial coherence interferometry (PCI), namely LenStar LS900 (Haag-Streit, Koeniz, Switzerland) and Allegro Biograph (Wavelight, Erlangen, Germany).
These devices have been shown to be as accurate and repeatable as the IOLMaster and also advantageous in capturing all unnecessary measurements of realignment and measurement of additional anterior chamber components such as corneal thickness for use in likely new biometric algorithms in the future.
Biometrics
A-scan ultrasound and keratometry measurements in children can be difficult or unattainable in the office. Most children need an exam under anesthesia (AUS).
Inaccurate axial length measurement is the most important source of error in calculating intraocular lens power, almost equivalent to 2.5 D / mm. In very short eyes (20mm), this error increases dramatically to 3.75 D / mm. Therefore, it is of great importance to minimize these errors.
Important details to note include the speed required for use in any given eye (phakic, aphakic, or pseudophakic) and the constant A for a specific intraocular lens.
Axial length measurements made with a contact technique have been reported to be, on average, 0.24 to 0.32 mm smaller than measurements made with a dip technique.
keratometry
Reliable autokeratometer devices should be used to accurately measure corneal curvature in pediatric eyes. To avoid inaccuracies when taking repeated measurements, it is recommended to take the mean value for calculating the power of the intraocular lens.
Intraocular Lens Power Calculation Formulas
In adult patients, several generations of intraocular lens power formulas have evolved, resulting in vast improvements in the accuracy of postoperative refractive prediction.
SRK-T, Holladay 1 and 2, Hoffer Q, and Haigis are commonly used formulas. Although in eyes with an average axial length, they differ only slightly in predicting the optimal power of the intraocular lens, some are more accurate than others for axial lengths outside the average.
The following guidelines have been recommended for the choice of formulas: 29 for axial length <22 mm, Hoffer Q or SRK / T; for axial length 22 to 24.5 mm, SRK / T, Holladay 1 or Hoffer Q; for axial length> 24.6, SRK / T.
Haigis and Holladay 2 are newer formulas and therefore not featured in previous guidelines.
Haigis’s formula also uses anterior chamber depth and uses three constants. In a large series, it has been shown to be more accurate than Hoffer Q in extreme farsightedness.
It was also found to be the most accurate for long eyes (axial length> 25.0mm).
The Holladay 2 formula uses seven variables: axial length, lens thickness, corneal power (mean K), target-to-target horizontal corneal diameter, anterior chamber depth, preoperative refraction, and patient age.
A study that investigated the precision of the prediction of intraocular lens power using the Hoffer Q, Holladay 1 and 2 and SRK / T formulas found no statistically significant differences between them in all subsets of axial lengths.
Now the question is what intraocular lens formula should be used in children? Due to the relatively large errors in intraocular lens formulations demonstrated in pediatric studies, no one formula can be considered accurate for all children.
Andreo and his colleagues reported that all formulas were slightly less accurate in eyes with a shorter axial length. In this group, the Hoffer Q formula had the lowest error (1.4 D) and the SRK-II had the highest error (1.8 D).
Although no formula has been shown to have an advantage, it is preferable to use theoretical formulas (for example, SRK-T, Holladay I and Hollday II, Hoffer I and II, Hoffer Q and Haigis) because they are generally more accurate for small eyes, and in studies pediatric seem to be a bit more accurate in general.
Individual surgeons continue to use their favorite formulas to give them intraocular lens calculations, but the newer formulas should help reduce residual refractive errors, especially in more extreme biometric cases.
Intraocular lens power selection
Children have growing eyes and rapidly developing visual systems. The eyes of normal children grow from an average axial length of 16.8 mm at birth to 23.6 mm in adult life.
Most of the axial growth occurs during the first two years of life, but there is no clear cut-off date; instead, the rate of change gradually decreases throughout childhood.
As the size of the eyes increases, the power of the optical component decreases proportionally. Natural lens power decreases from 34.4 to 18.8 D.
After the lens is surgically removed; Each millimeter of axial growth of the globe changes the refractive error of the eye by more than 2.5 D.
In contrast to the -0.9 D refractive change in normal phakic eyes, aphakic eyes have an average myopic shift of 10 D from infancy to adulthood. This is a myopic change of refraction, and not myopia.
Historically, three main approaches have been used for the selection of intraocular lens power in children: baseline high hyperopia, baseline emmetropia, or baseline low hyperopia.
Regardless of the approach chosen, the refraction is changing and is probably not stable until age 20. Therefore, regular follow-up visits and a regular change of correction are required for residual refraction.
Initial high farsightedness offers the advantage that with axial enlargement of one eye, the farsightedness will improve, and the refraction of the adult will likely be in or near the plane, therefore low myopia or low farsightedness can be achieved.
However, this advantage must be balanced by the fact that uncorrected hyperopic refractive error in children can cause or impair amblyopia.
Since the initial emmetropia reduces the risk of amblyopia, some surgeons prefer to target to help treat amlyopia. However, significant late myopia will become more apparent as the years go by, as young children’s eyes continue to grow.
So finding a compromise between these two extremes might be a better solution.
Most physicians who have been implanting intraocular lenses in young children have chosen a power intermediate between what the formulas would predict for the eye at implantation and what the expected adult power would be for the specific eye.
Most doctors who implant an intraocular lens consider the age at the time of surgery, the condition of the other eye, the likelihood of compliance with amblyopia therapy, etc.
When an intraocular lens is implanted in infancy, marked axial growth should be expected for the first 1 to 2 years after surgery.
Therefore, intraocular lenses implanted in childhood are generally selected to produce an undercorrection of 20% or more. The closer to birth, the more marked this undercorrection should be.
Companion eye status
It is important to consider the refractive state in the other eye. More farsightedness can be accepted when surgery is performed bilaterally, as noncompliance with lenses is less amblyogenic in such children, or in one eye with monocular cataract, if the other eye is pseudophakic.
Attempts should be made to minimize aniseikonia in these eyes.4
Visual acuity
Dense amblyopia can lead to a decision to less hyperopia (or even achieve emmetropia) in an effort to help regain vision by minimizing the need for glasses and emphasizing occlusion therapy.
In this case, late myopia is acceptable if it helps restore vision over years of treatment with amblyopia. Also, myopia can probably be more easily managed with refractive surgery.
Refractive error of parents
It has been observed that if both parents are myopic, 30% to 40% of their children will become myopic, while if only one parent is myopic, 20% to 25% of their children will become myopic.
If neither parent is nearsighted, less than 10% of their children will become nearsighted. Anticipating further growth of the eye, these children may be left with more initial hyperopia.
Amount of undercorrection
In general, the higher the power of the intraocular lens, the more lack of correction is needed. For example, at the age of 1 month, if a child has an emmetropic power of 50 D and another child of the same age has an emmetropic power of 40 D, the first child will require a higher residual hyperopic refraction.
In other words, one can consider an expected approximate refraction of +12 D in the first child, while in the second child + 10 D may be adequate.4
Effective intraocular lens enhanced by implantation site
If the intraocular lens fixation site needs to be changed during surgery, an appropriate adjustment may need to be made.
A higher power intraocular lens that travels further anteriorly in the eye will have a greater refractive effect compared to the relatively posterior location.
Intraocular placement of the intraocular lens will affect predicted error, with sulcus fixation producing a relative myopic displacement from pouch fixation.
The power of the intraocular lens for capsular bag placement should be decreased by 0.75 to 1.00 D (depending on the power of the intraocular lens) when placed in the ciliary groove.
Power calculation for secondary intraocular lens implantation
For secondary intraocular lenses, power can be calculated without axial length or corneal power values simply by using aphakic refraction.
The pediatric intraocular lens calculator can also be used to calculate intraocular lens power in secondary implantation.
Add the child’s age, the intraocular lens constant A, and an approximate corneal power and axial length value. Set a power of “0” for “intraocular lens power”, and the program will tell you the predicted “resultant refraction”.
Then adjust the axial length value until the “resulting refraction” equals the measured refraction for that eye. Finally, put in your “target refraction”; the resulting “intraocular lens to use” output must be accurate.
All known factors affecting axial growth must be taken into account. In addition to these, various other factors (eg, gender, race, etc.) have been reported to affect normal eye growth and may also influence eye growth after cataract surgery.
Surgeons implanting intraocular lenses in young children must be prepared for wide variability in long-term myopic change.
Both the magnitude of myopic change and the variance in this change are likely to be greater in children undergoing surgery in the first years of life.
Anticipation of this myopic change, and its proper correction or compensation, will help achieve better anatomical and functional results in young eyes undergoing cataract surgery.
Handling refractive surprises
Despite best efforts, refractive surprises do occur. This may be due to errors in biometrics and the use of inappropriate power calculation formulas. Sometimes, as a result of human error, the wrong lens can be implanted.
In each case of unexpected refractive result, the process should be reviewed to identify its precise reason. Hospital critical incident procedures should be invoked for a multidisciplinary approach in order to learn from mistakes and minimize risk in the future.
The unexpected refractive error could be predominantly spherical, cylindrical, or both. Unexpected astigmatism can be the result of a:
Poor wound construction (high surgically induced astigmatism), unplanned intraoperative conversion to a large incision to express lens fragments, or due to pre-existing high corneal astigmatism that had been masked by lenticular compensation.
Unexpected refractive errors need proper treatment, especially in patients prone to amblyopia.
Complications of intraocular lens implantation
Visual axis opacification
Secondary visual axis opacification is one of the most common complications of pediatric cataract surgery, especially when the posterior capsule is left intact.
Posterior capsular opacification is generally delayed in eyes with hydrophobic acrylic intraocular lenses compared to polymethylmethacrylate intraocular lenses.
Opacification of the visual axis after implantation of acrylic intraocular lenses with an intact posterior capsule is more “proliferative” compared to the “fibrous” reaction commonly seen in conjunction with polymethylmethacrylate intraocular lenses.
After primary posterior capsulectomy and anterior vitrectomy, visual axis opacification is rare in older children who receive an acrylic intraocular lens.
The opacification of the visual axis usually occurs in a baby operated in the first year of life. When infant eyes are implanted with an intraocular lens, visual axis opacification is common despite posterior capsulectomy and vitrectomy.
Using hydrophobic acrylic intraocular lenses, several articles have reported an average rate of 44.0% for visual axis opacification, ranging from 8.1% (review of children under 2 years old) to 80% (including operated children under 6 months) .
Secondary visual axis opacification in childhood implanted eyes tends to occur within the first 6 months after cataract surgery.
Therefore, longer follow-up probably does not change the incidence of visual axis opacification in infant eyes.
Eyes with ocular abnormalities (eg, anterior segment dysgenesis, iris hypoplasia, or persistent fetal vasculature) have a 9-fold increased risk of developing visual axis opacification compared to eyes without such abnormalities.
In children older than 2 years at the time of cataract surgery, the secondary visual axis opacification rate after primary posterior capsulectomy and vitrectomy ranges from 0% to 20.6% with an average of 5.1%.
In older children, some authors prefer to perform only posterior capsulorhexis (without vitrectomy).
The average rate of secondary intervention in these eyes is 13.8% (range 0-68%).
With an intact posterior capsule, several articles have reported posterior capsular opacification ranging from 14.7% to 100% (average 25.1%, excluding eyes with 100% posterior capsular opacification in children younger than 4 years of age).
While the biomaterial of the lens was originally believed to be a primary determinant, it is now widely recognized that the design of the intraocular lens, primarily a square edge of the optic, acts as a barrier to migration of these cells.
Improved square edge designs are now available providing a raised edge and consequently greater barrier function.
The optical properties of newer lenses would seriously degrade after capsular opacification and removal.
Posterior optic buttonholing is a technique whereby a 4 mm or smaller opening is made in the posterior capsule and the optic prolapsed into the opening.
This technique was adopted from pediatric cataract surgery where the rate of posterior capsular opacification after cataract surgery is extremely high. In a consecutive series of 1,000 patients, this technique has been shown to be safe and effective.
Amblyopia
In addition to their direct effects on vision, aphakia and other lens disorders in children can also cause visual loss due to amblyopia, especially in young infants with unilateral aphakia.
The onset of amblyopia in this setting is rapid and profound, and early intervention is necessary to maximize the chances of a good visual outcome. A good result in the optical correction of pediatric aphakia depends on 3 problems:
- Successful surgical removal of lens opacity.
- Replacement of the proper focusing power of the lens.
- The proper treatment of amblyopia.
The risk of amblyopia is greatly increased in younger children, and the younger the child, the greater the risk. Unilateral cataracts and aphakia in particular are highly amblyogenic in newborns.
They should be removed within 4 to 6 weeks of age to maximize the potential for good vision. Bilateral cataracts can also cause amblyopia in newborns, but the time frame for optimal removal in this setting is 2 to 3 months.
The risk of amblyopia in patients with acquired cataracts decreases as children grow older, but persists until 5 years of age or older. If an older child presents with a unilateral cataract, the prognosis for improvement depends on the age at which the opacity developed.
If it has been present since early childhood, the prognosis is poor due to amblyopia, even if the surgery itself is successful.
Ongoing treatment of amblyopia is critical in children with lens disorders, particularly infants with unilateral opacities. The patch is often necessary during the first few years of life to achieve the best possible vision.
Glaucoma
Glaucoma is one of the most common complications of congenital cataract surgery. It has been reported in 0% to 41% of cases.
Children do not cooperate well with the eye exam and intraocular pressure (IOP) measurement, so the diagnosis of glaucoma can be easily missed. Most cases of pediatric aphakic glaucoma are of the open-angle type and the prognosis is guarded.
The incidence of aphakic glaucoma also appears to increase with longer follow-up. Frequent and lifelong monitoring is required to detect glaucoma, as it can manifest many years after congenital cataract surgery.
Summary
The main function of the lens is to focus light on the retina. In aphakic patients, this focusing power must be replaced to restore vision. Options include aphakic lenses, aphakic contact lenses, and intraocular lenses.
Intraocular lenses are often the best option in older children, as they more closely restore the eye to its natural state. Many patients require glasses in addition to intraocular lenses to sharpen focus.
Since the intraocular lens has only one power in aphakic patients, a bifocal is needed to focus closely. Intraocular lenses are generally not implanted in early childhood, for two reasons.
First, the incidence of complications related to intraocular lenses, such as glaucoma, opacification of the visual axis, lens displacement, and inflammation is much higher in the first months of life.
Second, the eye grows rapidly during the first 1 to 2 years of life, and this growth affects refraction. Intraocular lenses are not adjustable, and a lens that focuses correctly in a 1-month-old child will be substantially overpowered by the age of 2.
Therefore, most babies with unilateral aphakia are treated with contact lenses during the first few years of life, after which an intraocular lens can be implanted as a secondary procedure.
Aphakic glasses are also an option to replace focusing power, but they are very thick and cause distortion. Parents / caregivers play a critical role in the postoperative care of the eye and the treatment of amblyopia after aphakia.
Frequent and lifelong monitoring is also necessary to detect glaucoma, as glaucoma can manifest several years after congenital cataract surgery.
Living with aphakia
Aphakia in both adults and children can be easily treated with surgery. Just be sure to follow up with regular eye exams to check for any complications.
