CHAPTER 23 COMPLICATIONS OF CATARACT SURGERY 223
23.What medication is associated with intraoperative floppy iris syndrome?
Tamsulosin (Flomax) is a systemic α1 antagonist medication used to treat prostatic hypertrophy. This drug relaxes the smooth muscle in the bladder neck and prostate. It has been postulated that the same receptor is present in the iris dilator smooth muscle, resulting in loss of normal iris muscle tone.
24.What are the indications for capsular tension rings?
Capsular tension rings may be used in a variety of patients. Most frequently they are used in patients with zonular laxity or instability. Most often this is in patients with pseudoexfoliation syndrome. It may also be a useful management tool in trauma cases or in patients who develop zonular dialysis as a result of the surgical procedure.
25.What complications have been reported with femtosecond laser-assisted cataract surgery?
•Increased incidence of anterior capsule tears compared with traditional phacoemulsification cataract surgery. Laser anterior capsulotomy integrity seems to be compromised by postage-stamp perforations. This leads to an increased incidence of anterior capsule tears compared with manual continuous capsulorrhexis.
•Incomplete anterior capsulotomy resulting in capsule tags or bridges
•Posterior capsule rupture possibly resulting in posterior dislocation of lens material2
26.What are the common reasons that patients may be unhappy with multifocal IOLs?
•Uncorrected refractive error (either myopia, hyperopia, or astigmatism).
•Ocular conditions that reduce contrast sensitivity or image quality that were undiagnosed prior to surgery, including but not limited to dry eye syndrome, anterior basement membrane dystrophy, macular degeneration, and/or epiretinal membrane.
•Loss of contrast sensitivity related to IOL design with resulting image quality degradation.
•Disabling glare or halos.
•Intermediate vision complaints.
•Decentered or tilted IOL.
27.What is the difference between positive and negative dysphotopsia?
•Negative dysphotopsia represents an undesired optical phenomenon after cataract surgery. It is classically described as a dark temporal shadow. It is seen only with in-the-bag posterior chamber with overlap of the anterior capsulorrhexis onto the anterior surface of the IOL. If disabling to the patient, it has been successfully treated with two surgical strategies: reverse optic capture (the lens optic is moved anterior to the capsulotomy) and placement of a secondary piggyback IOL.
•Positive dysphotopsia is characterized by light streaks, starbursts, or glare.
28.What are the reasons for residual astigmatism following toric IOL implantation?
•Implantation of a toric IOL on the wrong axis or rotation of the IOL off axis during the postoperative period.
•An effect of posterior corneal astigmatism. A recent study showed that posterior corneal astigmatism on average will increase against-the-rule astigmatism and decrease with-the-rule astigmatism.
•Irregular astigmatism. Patients with irregular astigmatism from keratoconus, corneal scars, and other causes are not good toric IOL candidates. Attempted correction may result in undesirable postoperative results.3
References
1.Jaffe GJ, Burton TC, Kuhn E, et al.: Progression of nonproliferative diabetic retinopathy and visual outcome after extracapsular cataract extraction and intraocular lens implantation, Am J Ophthalmol 114:448–459, 1992.
2.Abell RG, Davies PE, Phelan D, Goemann K, McPherson ZE, Vote BJ: Anterior capsulotomy integrity after femtosecond laser-assisted cataract surgery, Ophthalmology 121(1):17–24, January 2014.
3.Koch DD, Ali SF, Weikert MP, Shirayama M, Jenkins R, Wang LJ: Contribution of posterior corneal astigmatism to total corneal astigmatism, Cataract and Refractive Surg 38(12):2080–2087, December 2012.
CHAPTER 24
AMBLYOPIA
Lauren B. Yeager and Steven E. Brooks
1.What is amblyopia?
Amblyopia may be defined as a potentially reversible loss in visual function (e.g., acuity, contrast sensitivity, motion perception, binocularity), in one or both eyes, that results from inadequate or abnormal stimulation of the visual system during a critical period of early visual development.1
2.Explain the concept of the “critical” or “sensitive” period.
This period is central to the concept of amblyopia. It refers to a developmental time frame early in life during which there is robust plasticity within the visual system, particularly the visual cortex. Although not precisely defined, this period extends from birth to approximately 8 to 10 years of age. During this period the visual system is profoundly affected by the quality of visual stimulation it receives. Abnormal visual experience can lead to developmental abnormalities at both the structural and the functional level. If amblyopia occurs, it must be detected and treated during the critical period for vision to develop normally.2
3.How is amblyopia classified?
Amblyopia is classified according to the underlying mechanism: strabismic, optical defocus, pattern or form deprivation, and organic.
Strabismus can lead to amblyopia if one eye becomes dominant, which causes the afferent input from the deviating, nondominant eye to be chronically suppressed. Optical defocus encompasses anisometropia as well as bilateral severe ametropia. Pattern or form deprivation amblyopia is caused by lesions that physically obstruct the visual axis, such as a congenital cataract, corneal opacity, vitreous hemorrhage, or ptosis. Organic amblyopia occurs secondary to a defined lesion of the visual pathways, such as a macular scar or coloboma. It is fundamentally different from the other types, because some or all of the vision loss is irreversible, and not simply a secondary effect on receptive fields in the lateral geniculate nuclei and visual cortex.
4.How does strabismus cause amblyopia?
Manifest strabismus disrupts sensory fusion. As a result, the vision from one eye must be suppressed to avoid diplopia and visual confusion. If a child with strabismus develops a strong preference for the use of one eye over the other, the nondominant eye may become amblyopic because of chronic suppression.
5.How prevalent is amblyopia?
The incidence of amblyopia is 1% to 3.5% in developed countries, and it is the most common cause of unilateral vision loss in children and young adults.
6.What factors place children at increased risk for amblyopia?
•Developmental delay
•Positive family history of amblyopia
•Prematurity
These factors lead to a twoto sixfold increase in a child’s chance of developing amblyopia.
7.What anatomic changes have been shown to occur in amblyopia?
Extensive animal studies have shown several neuroanatomic alterations in amblyopia. The primary abnormality appears to be the atrophy of cells in the layers of the lateral geniculate nucleus and visual cortex serving the amblyopic eye. These changes can be partially or wholly reversed if the amblyopia is successfully treated.3-5
8.How early should children be screened for amblyopia?
The American Academy of Ophthalmology, American Academy of Pediatrics, and American Association of Pediatric Ophthalmology and Strabismus recommend routine vision screening in children by a pediatrician or properly trained health care provider as follows:
•In newborns in the newborn nursery
•At each routine well visit from 1 month to 4 years of age
•A formal visual acuity should be documented by 5 years of age, or earlier if possible
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CHAPTER 24 AMBLYOPIA 225
A
B
Figure 24-1. Child with esotropia showing spontaneous alternation in fixation. A, The left eye is used for fixation.
B, The right eye is used for fixation. Alternating fixation is good evidence against the presence of amblyopia in children with strabismus.
The optimal time to diagnose and treat amblyopia is as soon as it occurs, but it is critical to do so before the close of the critical period (ideally before the child is 5 years of age).6
9.What are some clinical techniques to check for amblyopia in nonverbal children?
Fixation preference testing is especially useful. In strabismic patients, a lack of spontaneous alternation in visual fixation between the two eyes suggests amblyopia in the nonpreferred eye (Fig. 24-1). In patients with straight eyes or small-angle strabismus the vertical prism test is used to determine fixation preference. A child who consistently objects to occlusion of one eye but not the other can be assumed to have decreased vision in the eye that he or she will allow to be covered. Visual evoked potentials and preferential looking (e.g., Teller acuity cards) tests can be used to measure visual acuity. The Bruckner test, comparing the quality and symmetry of the red reflex between the two eyes using a direct ophthalmoscope, can help detect small-angle strabismus or anisometropia.7-9
10.Describe photoscreening and its role in detecting amblyopia.
A photoscreener is a device used by pediatricians or other individuals to screen for amblyogenic risk factors in children. The photoscreener is a camera that takes multiple images of a child’s undilated eyes to detect amblyogenic risk factors including high refractive errors, anisometropia, anisocoria, and the presence of strabismus (Fig. 24-2). Children who are identified as having risk factors for amblyopia by the photoscreener should be referred to a pediatric ophthalmologist for a complete examination. Photoscreeners may have significant advantages over traditional eye chart acuity screening, especially in younger children who are preverbal or may not be able or willing to participate in the eye chart acuity test.
11.What is the usual presenting complaint of a child with anisometropic amblyopia and at what age does it occur?
Similar to other forms of amblyopia, anisometropic amblyopia is generally asymptomatic. Detection in children depends on effective screening programs. Because of the lack of an overt external sign, such as strabismus or ptosis, the average age at presentation for anisometropic amblyopia is approximately 5 to 6 years, when school-initiated screening programs begin.
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Figure 24-2. Image taken from a commercially available photoscreening device. Similar to the Bruckner test, the red reflex is evaluated. Based on the shape, size, and location of the bright crescents in the pupillary light reflexes of the undilated pupils, a determination can be made as to whether the child has significant refractive error, anisometropia, or strabismus. Digital analysis software available in many of the commercially available devices can analyze the images and provide referral recommendations to the tester.
12.How does anisometropia cause amblyopia?
In anisometropia the retinal image in one eye is always defocused. If fixation is not alternated, the chronically defocused eye becomes incapable of processing high-resolution images. In addition, the binocular rivalry between the blurred image in one eye and the clear image in the other eye leads to foveal suppression of the blurred image as a way to avoid visual confusion. In the absence of strabismus, the suppression affects the foveal region, where high-grade visual acuity is processed and binocular rivalry is poorly tolerated. As a result, such patients often display peripheral sensory fusion and gross stereopsis (monofixation syndrome) and maintain good ocular alignment.10,11
13.In addition to visual acuity, what other aspects of visual function may be affected in amblyopia?
•Binocular vision and stereoacuity
•Contrast sensitivity
•Motion perception and processing
•Spatial localization
14.Which is more likely to produce amblyopia—unilateral or bilateral ptosis? Why?
Unilateral ocular abnormalities are much more likely to lead to amblyopia than binocular ones. If one eye has a competitive advantage over the other, its afferent connections become stabilized and more numerous while those of the other eye atrophy and retract. This competition also forms the basis for treating amblyopia. The amblyopic eye, by one means or another, must be given a temporary competitive advantage over the dominant eye.
KEY POINTS: AMBLYOPIA FUNDAMENTALS
1. Amblyopia is a potentially reversible loss of vision caused by abnormal visual stimulation during early visual development.
2. The critical period for amblyopia extends from birth to ages 8 to 10 years.
3. Testing vision with isolated optotypes may overestimate acuity in amblyopia because the effects of crowding are eliminated.
4. Amblyopia is characterized by functional and structural changes in the visual cortex and lateral geniculate nuclei.
15.What steps should be taken before patching or penalization?
The first step is to identify and treat any organic causes for vision loss. The second step is to ensure a clear visual axis. For example, this may require removal of a congenital cataract or vitreous hemorrhage. Significant refractive errors should also be corrected. It may be helpful, during the course of treatment, to correct even relatively low degrees of hyperopia or astigmatism in the amblyopic eye, because the accommodative effort of an amblyopic eye is often reduced. Some cases of refractive amblyopia may be treated by wearing glasses alone, obviating or delaying the need for patching or penalization therapy.12
16.How effective is part-time patching compared with full-time patching?
Part-time patching is equally effective as full-time patching in the treatment of amblyopia. Greater compliance is seen with part-time patching regimens. With full-time occlusion there is a greater risk of amblyopia being induced in the sound eye. Children can safely receive full-time occlusion of the
CHAPTER 24 AMBLYOPIA 227
sound eye for up to 1 week per year of life before the next follow-up visit without significant risk of inducing occlusion amblyopia in the sound eye.
17.What is penalization and how is it used to treat amblyopia?
Penalization refers to the intentional degradation of visual acuity in the sound eye by either optical or pharmacologic means. For example, the sound eye might be effectively blurred by intentional undercorrection of its refractive error, using atropine drops to prevent accommodation, or both. Translucent filters can be placed over the spectacle lens of the sound eye to degrade the vision. Penalization techniques are best suited for patients with a high degree of hyperopic refractive error in the sound eye and in whom the amblyopia is mild to moderate (20/100 or better).13-16
18.At what point can amblyopia treatment be discontinued?
When the acuity in the treated eye is equal to that of the sound eye. The decision is less clear when there is some persistent deficit in visual acuity. If poor compliance can be ruled out, many practitioners continue to patch until no further improvement is noted after three consecutive treatment intervals (3 to 4 weeks per interval). The eye examination and refraction should also be repeated to detect uncorrected refractive error or structural lesions. These guidelines may be modified, especially if there is a component of organic amblyopia. Once treatment is discontinued, the child should be periodically rechecked to detect recurrences.
19.What are some of the factors affecting the success of amblyopia treatment?
•Age of onset
•Age at which treatment is initiated
•Compliance with treatment regimen
•Depth of amblyopia
•Presence of associated ocular anomalies or injuries
20.Can the vision of an amblyopic eye ever improve in adulthood?
Although the critical period has passed, significant improvements in adulthood have been reported in cases in which the sound eye was lost to enucleation. The presence of central fixation in the amblyopic eye before the loss of the sound eye seemed to be the single most important predictor of the extent of visual improvement.
Studies looking at the potential use of pharmacologic agents such as levodopa to recover vision from amblyopic eyes in visually mature patients have demonstrated only small and temporary improvements. Such agents are not used in routine clinical practice.17-21
21.Is color vision affected in amblyopia?
Generally speaking, color vision is not affected by amblyopia, although some investigators have found mild abnormalities in color perception. Eyes with severe amblyopia, particularly those with loss of foveal fixation, tend to demonstrate such abnormalities more consistently than eyes with milder degrees of amblyopia.
22.Does amblyopia cause a relative afferent pupillary defect?
Generally speaking, amblyopia does not cause an afferent pupillary defect (APD), because the pathologic changes in amblyopia are located in the posterior visual pathways, not in the retina or optic nerve. If an eye suspected of having amblyopia is found to have a relative APD, it is imperative that a retinal or optic nerve lesion is ruled out.22
23.In which of the following conditions is amblyopia most likely to occur: congenital esotropia, accommodative esotropia, intermittent exotropia, or constant exotropia?
Amblyopia is most likely to occur in accommodative esotropia. Patients with this condition, particularly if there is significant anisometropia, are less likely to alternate fixation than patients with congenital esotropia or exotropia. Patients with intermittent exotropia are unlikely to develop amblyopia, because they spend a fair amount of time being bifoveal.
24.What is the effect of neutral density filters on the vision of an amblyopic eye compared with a normal eye?
The visual acuity of a normal eye is progressively reduced by neutral density filters, whereas that of an amblyopic eye may remain unchanged or even improve slightly. This finding has led investigators to postulate that the vision in an amblyopic eye more closely resembles that normally occurring under scotopic conditions (i.e., rod mediated).