Prescribing Glasses for Aphakia

Indications

Visual consequences of aphakia are not the only concern. Patients require individualized care teams to address visual and pathological sequelae of aphakia.[5] Regarding visual demands, clinicians must consider the patient's age and risk for anisometropic amblyopia. Aphakia in one or both eyes influences refractive options greatly. The affected eye's visual potential and binocular function should be reviewed before offering visual therapeutic options like eyeglasses or contact lenses.

Aphakia with Age

Infantile and childhood cataracts occur in 3 to 6 persons per 10000 live births worldwide.[6][7][8] Cataracts in pediatric patients may be congenital, developmental, or traumatic.[9] Infantile cataracts are bilateral in nearly 65% of cases.[10] Cataracts found in children younger than 6 years are likely to cause amblyopia, while those older than 6 years have less risk of more severe forms of amblyopia.[11] To avoid deprivation amblyopia, lensectomy is the treatment of choice for infantile or childhood cataracts. 

An uncorrected aphakic eye, characterized by high refractive error and a lack of clear retinal image and sensory input, can adversely affect the development of the visual system. Thus, correcting the residual refractive error, particularly in infancy and childhood, is a top priority in reducing amblyopia risk. The decision to offer eyeglasses, contact lenses, or intraocular lens implantation requires in-depth conversations with the child's parents or guardians.

Eyeglasses may be heavy and difficult to keep on a small child's face; thus, contact lenses are often preferred as the first-line intervention in this age group. When considering corrective lenses for aphakia, it is essential to carefully evaluate and compare the risks, benefits, and alternatives associated with each option. In general, contact lenses are a preferred method of correcting both bilateral and unilateral cases of aphakia.[12]

Soft and rigid gas-permeable (RGP) contact lenses require careful handling, cleaning, and disinfection. Caregivers with difficulty applying, removing, and disinfecting the contact lenses may find eyeglass correction a more suitable option. The placement of an intraocular lens is debated since a child's eye changes dramatically in axial length and corneal curvature, making IOL predictions challenging.[13] Though this option is gaining popularity, outcomes in the IATS study show similar outcomes though surgical cases had greater complications.[14][15]

Refractive correction to provide a clear retinal image is only part of the treatment strategy. Regardless of lens type, amblyopia treatments should be reviewed and considered if the best-corrected acuity in the affected eye is worse than 20/20. Although there is no clear consensus on the duration of patching, some sources recommend amblyopia therapy until the child is at least 8 years.[16] These interventions develop and strengthen the visual processing systems.[9][11]

As the child grows, or if aphakia develops later in life, there may be greater interest in the corrective properties of contact or intraocular lenses. Patients and caregivers may spend more time weighing the benefits of different lens options, given the risk of amblyopia is less. There are benefits and limitations to all options, as previously outlined. In cases of unilateral aphakia or trauma, where damage to other ocular structures is documented, eyeglasses have limited success. 

Adult aphakia typically occurs in the setting of post-operation, trauma, or spontaneous dislocation of an intraocular lens.[17] As with the pediatric population, patients may be offered eyeglasses, contact lenses, or surgery. These options depend on the etiology of aphakia, laterality, and visual potential. 

Unilateral versus Bilateral Aphakia

Anisometropia, or a difference in prescriptions between eyes, is a consequence of unilateral aphakia. It is generally understood that each 1D of anisometropia corresponds to approximately a 1% difference in relative magnification between the eyes. The visual system can compensate for about 3% to 5% of relative magnification. In cases of mild anisometropia, modifying the base curve, center thickness, or refractive index of the lens material has been shown to minimize the effects of different retinal images, known as aniseikonia. 

When the relative magnification difference between the eyes exceeds 5%, it can lead to more significant aniseikonia, which often results in patients experiencing intolerance to eyeglass wear. Retinal rivalry and diminished stereopsis occur as a consequence of aniseikonia.[18] As the refractive correction moves closer to the ocular surface, differences in magnification are less pronounced. This makes contact lenses and intraocular lens implantation the preferred visual correction options in many patients with aphakia. 

Ultimately eyeglasses are not the first-line refractive option if visual potential exists in both eyes in a patient with unilateral aphakia. This is particularly true when the patient's visual processing system is still developing, and there is a risk of anisometropic amblyopia. In these cases, contact lenses or intraocular lenses are offered. However, eyeglasses might be considered in patients with bilateral or unilateral aphakia and visual potential in one eye with poor vision in the other eye.

Induced prism in anisometropic high plus lenses prescribed for aphakia may also lead to diplopia when the patient looks away from the optical center of the lens. f these cases, slab-off or reverse slab-off bifocals can be prescribed to avoid diplopia when looking into the bifocal. However, in other cases, single-vision glasses are indicated, and the patient must avoid looking too far away from the optical center of the lenses to avoid diplopia.[19][20]

Aphakia with Visual and Binocular Potential

In suppression or secondary diplopia cases, full correction of the suppressed or diplomatic eye becomes less desirable. If, coincidentally, the eye with aphakia is also the one with suppression or diplopia, it may be best to correct the dominant eye only and allow the brain to ignore the image in the uncorrected eye with aphakia. 

In trauma cases, contact lenses may offer a level of visual improvement relative to eyeglasses or IOL implantation, given that rigid gas-permeable lenses can mask underlying irregular astigmatism.[21][22][23]

Contraindications

Aphakia in childhood is one of the more clinically challenging clinical scenarios. Eyeglasses should be avoided when anisometropia exceeds 3.00 diopters of refractive error or 1.50 diopters of astigmatism due to the high risk of aniseikonia.[24] The crystalline lens has an average refractive power of 45 diopters at birth and 24 diopters in adulthood, and unilateral aphakia almost always causes anisometropia exceeding 3.00 diopters.[25][26]

Aniseikonia produces confusion, which may lead to permanent suppression, amblyopia, anomalous retinal correspondence, and concomitant strabismus development.[11] Since normal eye development involves changes in the refractive power of both the cornea and the crystalline lens and the axial length of the eye, removal or loss of the crystalline lens generally results in altered development of the pediatric aphakic eye.[27] 

Relative spectacle magnification in eyeglasses for unilateral aphakia poses a barrier to binocular vision leading to amblyopia. Another disadvantage of wearing glasses in newborns and infants is the extra weight and size of the high plus-power lens. Spectacles tend to be cosmetically, visually, and psychologically undesirable. Besides weight, high plus-power lenses also cause a ring scotoma, false orientation due to magnification, swim, and optical aberrations (chromatic, spherical, coma), which can be especially detrimental for young and active individuals.[28] 

Another problem that applies to both unilateral and bilateral aphakic spectacle lenses is that minor alterations in the vertex distance and pantoscopic tilt and alignment of the optical center of the lens with the pupil can cause an inaccurate refractive correction.[28] Anisometropic spectacle correction often results in diplopia when the visual axis is not aligned with the optical centers of the lenses. This limits the use of bifocals and may force the patient to avoid moving their gaze away from the optical centers of the lenses.[20]

Ultimately, glasses may remain an option in children in rare situations or when the parents refuse to apply and remove a contact lens.[4] Contact lenses pose risks of infection or complications. Discussions are necessary to review eyeglass correction or secondary intraocular lens implantation in high-risk or noncompliant cases. As IOL implantation becomes more common, the situation where this would be contraindicated usually involves age and visual development. Children younger than 3 years are poor candidates for IOL placement due to a greater risk of visual axis opacities. A better option may be to wait until the refractive error has stabilized, typically around the age of 4 or 5 years, before considering IOL implantation.

Equipment

To manage refractive options for patients with aphakia, ophthalmic care providers require at least a phoropter, though auto-refractors and retinoscopes can be useful to measure refractive error more objectively, particularly in pediatric populations. A keratometer or corneal typographer, which provides corneal size, curvature, and shape information, is necessary for contact lens fittings. 

Eyeglass prescriptions are fulfilled through optical, where specific measurements should be collected. Although online eyeglass companies exist, eyeglasses for aphakia have high prescriptions and leave little room for error. Thus, working closely with a knowledgeable optician helps reduce error and provides a resource to troubleshoot if the patient has trouble adapting to the prescription.

Many, but not all, contact lenses are designed through placed diagnostic lenses on an individual's eye to assess the fit and contact lens over-refraction. In more challenging cases, contact lens parameters can be predetermined through empirical calculations. Contact lenses for aphakia are usually specialized or customized for an individual; special agreements or accounts between the eye care provider and the manufacturer are required to fulfill these lens orders. 

Sometimes cases require additional surgeries. When a patient is undergoing a secondary IOL placement, the patient is referred to a surgeon. Surgeons need specific measurements to calculate IOL power. The IOL is placed in a surgical center or hospital operating room under sterile conditions. These procedures require a team within the operating room to ensure the patient safely receives the correct IOL and recovers as expected.

Personnel

In the United States, this type of issue is managed by various professionals in eye care. Optometrists and ophthalmologists frequently collaborate in the management of patients with aphakia. Since each case is individualized, the role of each provider varies. Nonsurgical management, such as spectacle measurements, contact lens fitting, amblyopia, and strabismus management, may involve the optometrist, ophthalmologist, or both. Surgical interventions are performed exclusively by an ophthalmologist.

Complications

When correcting aphakia during critical phases of visual development, the top priority is the prevention of amblyopia. Providers must remain mindful of patients in these vulnerable stages to ensure that refractive choices and amblyopia therapies are aggressive enough to improve or maintain vision. If there is an incomplete correction of aphakia, patients might experience a permanent loss of depth perception; this could increase the likelihood of accidents.

Eyeglasses

• High-powered lenses create magnification of eyes and face, possibly impacting self-image 
• Reduced peripheral vision
• Prismatic effect off-axis[20]

Contact Lenses

• Lost or broken lenses
• Hyperemia
• Superficial punctate keratitis
• Contact lens-induced red eyes 
• Microbial keratitis 
• Contact lens dropout due to challenges applying or removing lenses, cost, or adherence to the schedule[29][30][31][32]

IOL Implantation (lists are not exhaustive)

• Pediatric
  • More surgeries
  • Lens reproliferation
  • Pupillary membranes
  • Corectopia[15]
• Adult/Pediatric
  • IOL decentration, tilt, or dislocation
  • Pupillary optic capture
  • Suture or haptic erosion 
  • Corneal edema
  • Chronic uveitis
  • Cystoid macular edema
  • Endophthalmitis[33] 
• No Correction or Poor Visual Outcomes
  • Amblyopia
  • Suppression 
  • Sensory tropia 
  • Worse quality of life[34]

Clinical Significance

Once the crystalline lens is surgically excised from the eye, the overall power of the eye has lessened. A high-powered plus (eyeglass, contact, or intraocular) lens is necessary to focus light onto the retina. Eyeglasses cause relative magnification of the image subtended on the retina. For a patient with bilateral aphakia, eyeglasses can work well if the level of difference does not exceed three diopters.[4] 

Even with a balanced prescription, patients may complain of diplopia from induced prism when looking off-axis, a ring scotoma or "jack-in-the-box" effect, or cosmetic concerns from the lens magnification. Certain eyeglass materials in high prescriptions cause colorful distortions when viewing lights, known as chromatic aberrations.

When electing to use eyeglasses as the preferred method of vision correction, the eyecare provider should carefully consider several things. First, is the frame selection; a larger frame produces a thicker lens centrally, making the eyeglasses heavier and possibly harder to tolerate. Avoiding rimless or semi-rimless frames is typically advised. One option is to offer a lenticulated carrier for high-plus lenses.[35][36] This is a thin lens carrier holding a small high-powered 'button' centrally to allow for reduced center thickness. In general, the success of glasses may be improved by optimizing the cosmesis of the lens and the weight of the entire frame.

Often young children younger than 4 years are purposely over-plussed meaning slightly overcorrected for nearsightedness, to compensate for the potential development of hyperopia (farsightedness) as they grow. This over-correction resulting in mild myopia is ideal given the small stature and short working distance of infants and toddlers. Once children reach age 4, it is crucial to include bifocal correction to promote clear images at both distance and near. Recall that patients with aphakia lack accommodation and cannot focus in near-field vision. Therefore, these patients may require prescriptions for various focal distances. This may come in the form of multiple pairs of eyeglasses or multifocal correction. Lined bifocals, including flat-top, round segment, and executive designs, have been utilized, but progressive addition lenses could be considered once the child is considered mature enough to use these effectively.[37]

Ultimately, contact lenses and intraocular implantation are frequently utilized to reduce the effects of relative spectacle magnification. RGP contact lenses tend to be the preferred form of contact lens correction due to their small size and rigid material, making lens application and removal easier in pediatric cases.[38][12]

The evolution of silicone hydrogel in soft materials has made these lens options perfectly acceptable. RGP contact lenses remain the most ideal form of correction, particularly in traumatic cases that result in the irregularity of the corneal surface. Any induced irregular corneal astigmatism would be masked by the RGP contact lens and, thus, is the preferred modality.[23]

In the absence of a crystalline lens, there is greater exposure to ultraviolet radiation (UV). Thus, UV protection is an important consideration. While the sunglasses may not have a refractive correction, it is important to remind patients of this protective eyewear. Lastly, in patients who might not utilize eyeglasses for refractive error purposes, eyecare providers must continue to show vigilance in recommending protective eyewear and lenses with impact-resistant properties, particularly in cases of reduced monocular vision. 

Conclusions

Aphakia is a condition that affects individuals of all ages, genders, and ethnicities. Improvements in contact lens materials and surgical techniques have allowed for more options to manage the significant vision change induced by aphakia, including reduced vision and lack of accommodation. While eyeglasses might not be a first-line option in most cases, they should still be considered in case-by-case situations.

Enhancing Healthcare Team Outcomes

To optimize patient outcomes and reduce complications, eye care providers should maintain an open line of communication regarding the risks, benefits, and outcomes of each intervention. Patient expectations and demands may change with age; thus, an intervention that works today may not work in the future. As more research is published on secondary IOL placement, this option may potentially be offered as one of the earlier interventions instead of contact lenses.