Astigmatism

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Please note that formulations/routes and doses may differ between drug names and brands, drug formularies, or locations. Treatment recommendations are specific to patient groups: see disclaimer

ACUTE

borderline astigmatism in patients ages ≥1 year

1st line – monitoring or spectacle/contact lens correction

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1st line –

monitoring or spectacle/contact lens correction

Patient age determines the definition of borderline astigmatism. Treatment is indicated when eye strain (asthenopia) is present and typically involves spectacle or contact lens correction. All other patients with borderline astigmatism can be monitored at 3-6 month intervals.

Follow the recommended screening program and manage patients according to local or national criteria by age.[30][31][34][51]

regular astigmatism

infants ages <1 year

1st line – regular follow-up ± spectacle correction

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1st line –

regular follow-up ± spectacle correction

Spectacle correction is not usually necessary in this age group, because the visual blur does not seem to increase the risk of developing amblyopia. When no (or a small amount of) astigmatism is found, a follow-up exam should be scheduled at the next age interval. High degrees of astigmatism (≥1 diopter) necessitate follow-up exams at 3- to 6-month intervals.[52][53] It is acceptable to give spectacle correction in this age group when isometropic astigmatism is measured at ≥3 diopters and anisometropic astigmatism is measured at ≥2.5 diopters between eyes (in the absence of strabismus).[31]

children ages 1-3 years

1st line – consider spectacle undercorrection

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1st line –

consider spectacle undercorrection

When astigmatism is borderline (i.e., approximately 1-2 diopters), prescription is not obligatory and repeat retinoscopy at 3- to 6-month intervals is indicated. When repeat measurements demonstrate a stable or an increasing amount of astigmatism (≥2.5 diopter for isometropia or a ≥2 diopter difference between eyes for anisometropia without strabismus), spectacle undercorrection is recommended.[31] Undercorrection of the astigmatism should be accompanied by an adjustment of the sphere power. Leaving the child with a mild degree of blur allows further correction of refractive error (emmetropization). Astigmatism of <1 diopter does not usually require treatment and can be monitored at 6-month intervals.[54]

children ages 3-5 years

1st line – consider spectacle full correction

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1st line –

consider spectacle full correction

Astigmatism ≥2 diopter for isometropia or ≥1.5 diopter difference between eyes for anisometropia without strabismus requires full correction with spectacles. Note that thresholds to correct anisometropia should be reduced if the child has strabismus or amblyopia.[31][55] When a child exhibits good visual acuity and binocular function, they can wear the astigmatic correction as needed and return annually. However, in children <5 years old, refraction should be monitored every 3-6 months. Astigmatism of <1 diopter does not usually require treatment and can be monitored at 6-month intervals.

children ages ≥5 years

1st line – consider spectacle or contact lens full correction

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1st line –

consider spectacle or contact lens full correction

In older children and young adults with a significant amount of astigmatism (≥0.75 diopter), refractive correction is determined by the severity of the refractive error, visual acuity, and visual symptoms.[31] Full spectacle correction is usually needed to reduce the astigmatic correction (with adjustment of the sphere power), although patients may not be fully adherent. Full correction is mandatory if amblyopia is present. Older children may benefit from soft or rigid gas-permeable contact lenses as an alternative to spectacles. However, rigid lens prescriptions have diminished due to the increased use of soft toric lenses, even for higher levels of astigmatism.

ages ≥18 years

1st line – consider spectacle or contact lens full correction

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1st line –

consider spectacle or contact lens full correction

Full correction of the astigmatism with spectacles is required, though it is possible to reduce the astigmatic correction (with adjustment of the sphere power accordingly) in nonadherent patients. Alternatives to spectacles include soft or rigid gas-permeable contact lens prescription or, if not contraindicated, refractive surgery. Patients with low degrees of astigmatism (0.50 to 0.75 diopter in this age group) and high degrees of myopia or hyperopia may sometimes benefit from correction of the spherical error alone.

2nd line – refractive surgery

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2nd line –

refractive surgery

Laser refractive surgery is quickly gaining popularity.[42] The two most common procedures are photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK). Other options exist, such as astigmatic keratotomy and small-incision lenticule extraction (SMILE), with the latter avoiding the need for a corneal flap. Phakic intraocular lens implantation is also effective for correcting myopia and myopic astigmatism.[56]

In PRK, the anterior surface of the cornea is reshaped using laser energy, while in LASIK the laser is used to remove tissue from the corneal stroma after raising a lenticular corneal flap. LASIK appears to produce comparable visual acuity whether using a mechanical microkeratome or a femtosecond laser in patients with >0.5 diopter of myopic astigmatism.[57] One review comparing wavefront versus conventional refractive surgery and wavefront‐optimized versus wavefront‐guided surgery also found no differences in uncorrected visual acuity, residual refractive errors, or residual higher‐order aberrations between groups at 6-12 months.[58]

The full list of indications is extensive and should be checked against local guidelines and product literature (e.g., FDA approved lasers). FDA: FDA-approved lasers for LASIK / patient information Opens in new window The procedures are generally contraindicated with unstable refraction, corneal abnormalities, thin corneas, uncontrolled ophthalmic disease (e.g., glaucoma, blepharitis, dry eye, atopy, autoimmune disease), and unrealistic expectations or untreated mental illness.[42]

Good management requires informed consent (e.g., adverse effects include dry eye, eventual presbyopia, ectasia, and diffuse lamellar keratitis) and both the provision and maintenance of a clear record of the procedure (e.g., diagnosis, preoperative keratometry measurement, and both preoperative and postoperative refraction).[42][57] These records can be useful for future eye care (e.g., cataract surgery).

irregular astigmatism

keratoconus-related

1st line – spectacle or rigid gas-permeable (RGP) contact lens correction

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1st line –

spectacle or rigid gas-permeable (RGP) contact lens correction

Very mild cases (keratometry <45 diopter) can be handled with spectacle correction. However, most patients do not achieve satisfactory visual acuity and therefore require RGP contact lenses. Possible alternatives for RGP lenses are piggy-back, hybrid, or scleral lenses. In severe and refractory cases, keratoplasty is indicated. For most keratoconic patients, the keratometer reading and corneal topography are used only as a rough starting point in determining the lens base curve. The final adjustment is made by evaluating the fluorescein pattern with a diagnostic contact lens on the cornea.

2nd line – piggy-back, hybrid, or scleral lenses

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2nd line –

piggy-back, hybrid, or scleral lenses

Acceptable alternatives to rigid gas-permeable (RGP) contact lenses are piggy-back, hybrid, or scleral lenses.[1]

If keratoconic patients become intolerant of RGP lenses, it is possible to use a rigid lens fitted over a hydrogel lens (piggy-back lenses) to improve comfort and to provide an adequate wearing time with good visual acuity. The downsides of this technique are the handling and maintenance of two types of lenses, the difficulty in providing sufficient oxygenation to the cornea, and difficult centration of the rigid lens over the hydrogel one.

Hybrid lenses overcome the handling problems of piggy-back lenses, combining the optics of a rigid lens with the comfort of a hydrogel lens in one piece. This is done by forming a soft rim onto a hard central portion. Hybrid lenses have numerous potential problems, but they are useful for some patients with keratoconus and other corneal distortions.

Scleral lenses are very large rigid lenses, the haptic portion of which rests on the sclera. They provide excellent optics by neutralizing the distorted cornea and are surprisingly comfortable and easy to use. Their major disadvantages are the time and skill required in fitting the lens and their cost.

3rd line – intrastromal corneal ring segment (INTACS) inserts

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3rd line –

intrastromal corneal ring segment (INTACS) inserts

INTACS corneal implants are micro-thin rings that are inserted into the corneal stroma. It is a surgical procedure in which the inserted implants reshape the corneal curvature from within, thus modifying its refractive power. INTACS implantation can improve visual acuity and refraction in most patients with keratoconus. Infectious keratitis, a possible sight-threatening complication, has been reported.[59]

3rd line – corneal cross-linking

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3rd line –

corneal cross-linking

Collagen cross-linking by the photosensitizer riboflavin and ultraviolet-A light (epithelium-off cross-linking) seems to be effective in stabilizing the cornea and might delay the progression of keratoconus.[60][61]

Transepithelial cross-linking, in which the epithelium is retained, may potentially reduce patient discomfort and time to healing. There is, however, a lack of evidence to confirm these putative benefits.[61]

3rd line – topography-guided excimer laser surgery

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3rd line –

topography-guided excimer laser surgery

Mild to moderate keratoconus can be managed by photorefractive keratectomy (PRK), in which an excimer laser is used for customized ablation of the superficial corneal layers, thereby modifying their topography. PRK improved videokeratography indices and visual acuity in these patients over a 2-year follow-up period.[62]

3rd line – toric intraocular lens implantation

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3rd line –

toric intraocular lens implantation

When cataract surgery is considered in patients with stable keratoconus for a period of at least one year, toric intraocular lens may be implanted if maximal keratometry reading is less than 55 diopter.[65]

3rd line – photoastigmatic refractive keratectomy

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3rd line –

photoastigmatic refractive keratectomy

In photoastigmatic refractive keratectomy (PARK), the excimer laser is used to form a corneal slit, the width of which is determined by the degree of astigmatism. It has been shown to be safe and effective in mild keratoconus and in carefully selected patients with refractive and corneal stability.[63][64]

4th line – penetrating or deep lamellar keratoplasty

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4th line –

penetrating or deep lamellar keratoplasty

Keratoplasty (corneal grafting) can be penetrating (full corneal graft) or deep lamellar (partial thickness corneal graft). This modality should be considered in severe and refractory cases. Partial thickness corneal grafting is indicated only when the host cornea is partially intact (epithelial or endothelial part). Though the surgical technique for deep lamellar grafting is more difficult than penetrating keratoplasty, the healing process is shorter and therefore it is preferred when indicated.[36]

postkeratoplasty

1st line – spectacle correction

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1st line –

spectacle correction

The healing process following penetrating keratoplasty is long and may extend beyond 1 year. During that period, the patient's refractive error may fluctuate significantly and so it is wise to postpone the optical correction until relative stability is reached.

Generally, mild cases can be handled with spectacle correction; high degrees of astigmatism usually require other treatment modalities.

2nd line – selective suture removal

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2nd line –

selective suture removal

One way to combat high amounts of astigmatism is to selectively remove some of the sutures. Keratometry and corneal topography are used to monitor and determine the cylinder axis, and the sutures that are in the steepest meridian are removed first to decrease corneal steepness and to minimize its distortion. However, the response of the corneal surface to suture removal may be unpredictable and complex.[37][38]

3rd line – rigid gas-permeable (RGP) contact lenses

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3rd line –

rigid gas-permeable (RGP) contact lenses

Most patients postkeratoplasty have distorted corneas, necessitating refractive correction with RGP contact lenses. It is recommended to wait at least 3 months following surgery before fitting contact lenses. Because the edge of the transplant tends to be slightly raised with respect to the surrounding cornea, it may create problems in fitting RGP contact lenses; therefore, waiting until after suture removal is preferred.

4th line – piggy-back, hybrid, or scleral lenses

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4th line –

piggy-back, hybrid, or scleral lenses

These types of lenses can be used, but they have a tendency to encourage corneal blood vessel growth. Therefore, rigid gas-permeable lenses are preferred.

postcorneal trauma or scarring

1st line – rigid gas-permeable (RGP) contact lenses

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1st line –

rigid gas-permeable (RGP) contact lenses

Most patients with corneal trauma or scarring have distorted corneas, necessitating refractive correction with RGP contact lenses. These lenses are required to neutralize the corneal curvature and provide good optical results.

2nd line – spectacle or soft contact lens full correction

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2nd line –

spectacle or soft contact lens full correction

Correction of astigmatism in this group by spectacles or soft contact lenses is not likely to achieve satisfactory visual acuity, but in mild cases it is acceptable to try. The dimensions and power of the contact lenses are determined as for the keratoconic patients using the keratometric reading and corneal topography only as a rough starting point, making the final adjustment by evaluating the fluorescein pattern with a diagnostic contact lens on the cornea.

3rd line – piggy-back, hybrid, or scleral lenses

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3rd line –

piggy-back, hybrid, or scleral lenses

Because corneal trauma can produce a wide variety of corneal distortion patterns, case management is individualized. Acceptable alternatives to rigid gas-permeable contact lenses are piggy-back, hybrid, or scleral lenses. These lenses reduce discomfort while retaining the benefit of rigid optics.

Piggy-back lenses consist of a rigid lens fitted over a hydrogel lens to improve comfort and to provide an adequate wearing time with good visual acuity. Disadvantages of this approach include handling and maintenance of two types of lenses, providing sufficient oxygenation to the cornea, and difficult centration of the rigid lens over the hydrogel one.

Hybrid lenses combine the optics of a rigid lens with the comfort of a hydrogel lens in 1 piece. This is done by forming a soft rim onto a hard central portion. Hybrid lenses have numerous potential problems, but they are useful for some patients with keratoconus and other corneal distortions.

4th line – penetrating or deep lamellar keratoplasty

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4th line –

penetrating or deep lamellar keratoplasty

Keratoplasty (corneal grafting) can be penetrating (full corneal graft) or deep lamellar (partial thickness corneal graft). This modality should be considered in severe and refractory cases. Partial thickness corneal grafting is indicated only when the host cornea is partially intact (epithelial or endothelial part). Although the surgical technique for deep lamellar grafting is more difficult than penetrating keratoplasty, the healing process is shorter and therefore it is preferred when indicated.[36]

pterygium-related

1st line – spectacle correction

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1st line –

spectacle correction

Pterygium is a benign growth of the conjunctiva, commonly encountered on the nasal side of the sclera, though the temporal side may also be involved. The pterygium can induce a refractive change that often leads to visual impairment in a mechanism that is not totally clear. It has been shown to have a considerable effect on topographic indices of the cornea, presenting as flattening in the horizontal meridian, which is associated with astigmatism. The pterygium size appears to be related to the magnitude of the induced astigmatism. When a small pterygium is associated with a low-degree astigmatism, it is acceptable to attempt spectacle correction.[68]

2nd line – excision of the pterygium

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2nd line –

excision of the pterygium

Larger pterygia adversely affect astigmatism, asymmetry, and irregularity of the cornea. Pterygium >45% of the corneal radius may induce significant degrees of astigmatism. Indeed, one of the indications for pterygium removal is visual impairment. The surgery usually leads to reduced astigmatism and improved corneal topography, regularity, and symmetry.

eyelid pathology-related

1st line – treat underlying primary eyelid pathology

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1st line –

treat underlying primary eyelid pathology

Pressure from the eyelids has been shown to induce short- and long-term corneal topographic changes. Such changes in corneal topography and corneal astigmatism accompany certain common eyelid abnormalities (e.g., chalazia, capillary hemangioma). Disorders of eyelid position (e.g., ptosis) and surgery on the eyelids have also been found to cause changes in corneal topography and astigmatism. The magnitude of astigmatism is reduced by treating the primary eyelid pathology (e.g., excision of the chalazion, ptosis repair).[69][70]

during cataract surgery

1st line – intrasurgical correction

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1st line –

intrasurgical correction

Cataract surgery can serve as a good opportunity to reduce or even cancel preexisting astigmatism. Limbal relaxing incisions are best reserved for patients with low levels of astigmatism. However, toric intraocular lens implantation is the most predictable and cost effective method to correct high amounts of astigmatism.[42] Other intrasurgical options for treating residual astigmatism are to place the clear corneal incision on the steepest meridian (less effective with modern techniques) or to perform a two-stage procedure with excimer laser ablation (more predictable but expensive).[74]

Lenticular refractive surgery may be preferable to keratorefractive surgery for early cataract formation in the presence of significant lenticular astigmatism.[42]

following eye surgery

1st line – spectacle or contact lens correction

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1st line –

spectacle or contact lens correction

Some eye surgeries can give rise to astigmatism. The corneal incisions in cataract surgery induce variable amounts of astigmatism, the degree of which is influenced by the size, architecture, and location of the incision. Therefore, small incisions, associated with a more rapid wound healing and less corneal distortion, are preferred. Buckle procedure for retinal detachment and other eye surgeries are also associated with altered corneal surface indices and astigmatism. When astigmatism is mild, it is acceptable to use spectacle or contact lens correction.

2nd line – refractive surgery

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2nd line –

refractive surgery

When astigmatism is of greater magnitude, spectacle or contact lens correction may be insufficient. In these cases, several surgical techniques can be used. In astigmatic keratotomy (AK), arcuate incisions are placed along the full arc of the steep area and the level of astigmatic correction is controlled by varying the incision depth. This technique allows accurate control of the level of astigmatic correction with minimal risk. Alternatively, photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) is effective and safe for correcting residual astigmatism after cataract surgery.[71][72][73]

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Astigmatism

Treatment algorithm

borderline astigmatism in patients ages ≥1 year

monitoring or spectacle/contact lens correction

regular astigmatism

regular follow-up ± spectacle correction

consider spectacle undercorrection

consider spectacle full correction

consider spectacle or contact lens full correction

consider spectacle or contact lens full correction

refractive surgery

irregular astigmatism

spectacle or rigid gas-permeable (RGP) contact lens correction

piggy-back, hybrid, or scleral lenses

intrastromal corneal ring segment (INTACS) inserts

corneal cross-linking

topography-guided excimer laser surgery

toric intraocular lens implantation

photoastigmatic refractive keratectomy

penetrating or deep lamellar keratoplasty

spectacle correction

selective suture removal

rigid gas-permeable (RGP) contact lenses

piggy-back, hybrid, or scleral lenses

rigid gas-permeable (RGP) contact lenses

spectacle or soft contact lens full correction

piggy-back, hybrid, or scleral lenses

penetrating or deep lamellar keratoplasty

spectacle correction

excision of the pterygium

treat underlying primary eyelid pathology

intrasurgical correction

spectacle or contact lens correction

refractive surgery