Key Features
Ophthalmic and medical considerations in the preoperative evaluation of lens surgery include:
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The morphology of lens opacities and the effects and diagnosis thereof.
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The optics of the eye, including refractive correction modalities.
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The biometric measurements in standard and nonstandard eyes.
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The optimal medical assessment of the patient for surgery.
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The social and legal considerations in final aspects of the workup are discussed.
Introduction
Any patient undergoing cataract surgery requires an accurate ophthalmological workup and careful anamnesis. Although most cataract procedures are uneventful with regard to the patient’s medical condition, any problem or crisis is potentially ruinous, especially if surgery becomes complicated or prolonged. Therefore it is incumbent on the surgical, anesthetic, nursing, and family doctor teams to be fully aware of their patient’s surgical and medical status.
Medical History and Current Therapeutic Regimen
A history of cardiac, bronchopulmonary, or cerebrovascular incidents influences the timing and management of surgery, especially if it is recent. Diabetes mellitus and systemic hypertension are common in the population predisposed to operable cataract formation, and these conditions may adversely influence both the surgery and the postoperative course of events. Ram and coworkers carried out a study of more than 6000 patients who underwent cataract surgery and discovered multiple morbidities that arose from a variety of conditions. The major causes included pulmonary disease, cardiovascular and hypertensive disorders, diabetes mellitus, and significant orodental problems that required intervention.
Ram et al . also noted significant postoperative problems in 1.27% of their patients, nearly half of whom required hospitalization. Fisher and Cunningham and Hamed et al. noted an even higher morbidity in their cohort of patients who had cataract surgery ( Table 5.4.1 ).
| Condition | Percentage |
|---|---|
| Significant medical history | 84 |
| Diabetes mellitus | 16 |
| Systemic hypertension | 47 |
| Ischemic heart disease | 38 |
| Hypothyroidism | 18 |
| Undiagnosed tumors | 3 |
There are many factors that may affect cooperation and difficulty during surgery, varying from ventilation difficulties to substance abuse (including examination of identified cataract morphological findings), that may influence both the surgeon’s and the anesthesiologist’s decision about the form of anesthetic to use and the sedation required and potentially both the pre- and postoperative management ( Table 5.4.1 and 5.4.2 ).
| Systemic Disorder | Appearance in the Eye |
|---|---|
| Myotonic dystrophy | Blue dot cortical cataract and posterior subcapsular cataract |
| Wilson’s disease | Green sunflower cataract (copper) anterior or posterior subcapsular |
| Atopic dermatitis | Blue dot cortical cataract and posterior subcapsular cataract |
| Hypocalcemia | Discrete white cortical opacities |
| Diabetes mellitus | Snowflake opacities located in anterior and posterior subcapsular cortex |
| Acute onset diabetes | Cortical wedges caused by lens fiber swelling |
| Down syndrome | Snowflake opacities located in anterior and posterior subcapsular cortex |
| Systemic conditions requiring corticosteroids (any form of administration) | Posterior subcapsular lens opacities |
General Ophthalmic History and Examination
Both eyes are assessed fully by routine ophthalmological workup, which includes tonometry, slit-lamp biomicroscope examination, and posterior segment observations under mydriasis to estimate the visual outcome and risk category of surgery for the patient. Intercurrent ophthalmic disorders may prejudice the visual outcome. For example, uveitis may be exacerbated, herpes zoster may have left an anesthetic cornea, atopic disease may predispose the eye to infection, and Fuchs’ endothelial dystrophy may predispose the eye to corneal edema. Diabetes mellitus increases the prospects of postoperative macular edema.
The presence of open-angle glaucoma warrants further comment. The aforementioned disease processes need pickup and assessment to avoid deleterious effect on the eye after cataract surgery. The action of successful cataract surgery on glaucoma and ocular hypertension, however, has been demonstrated to have a positive effect on intraocular pressure (IOP) control.
With the advent of the new minimally invasive glaucoma surgery (MIGS) procedures, the surgeon should now consider using one of these devices at the end (or beginning) of a cataract procedure to further facilitate improved aqueous outflow, lower IOP, and improve glaucoma control, potentially reducing or eliminating the use of topical glaucoma drugs, which themselves can have an adverse influence on the ocular surface and visual quality both before and after cataract surgery. There are a number of MIGS devices available; see a commonly used example at Fig. 5.4.1 .
Patient counseling on the procedure and explanation of postoperative expectation are vital elements of the preoperative workup. A written explanation of the background and process of cataract surgery is invaluable.
Assessment of Lens Opacities
Introduction
The progressive insolubilization of lens protein with age is believed to cause refractive index and density fluctuations, which scatter light and impair vision.
The impact of a patient’s cataract on the retinal image may be appreciated on funduscopic examination, which can show interference with the red reflex and show the blur of fine retinal vessels.
Diagnosis of Lens Opacities
Slit-lamp biomicroscopy is the major method used to observe and assess cataracts. However, the image seen often fails to correlate with the patient’s visual acuity or function. The relationship between alterations in the structural proteins, the increase in light scatter associated with conventional biomicroscopy, and the capacity of visual function is not a simple one. For all lens examinations, the pupil is dilated maximally.
Classification of Lens Opacities
Nuclear Opacities
Initially, an increase in optical density of the nucleus occurs (nuclear sclerosis). The fetal nucleus is first involved and then the whole adult nucleus. The increase in density is followed by an opacification, which implies a change in color, namely from an initial clear to yellow to a subsequent brown (brunescent cataract).
In certain instances, crystals appear in the adult nucleus (or in the cortex, usually posteriorly) that, on slit-lamp examination, appear to be of different colors (polychromatic luster).
Cortical Opacities
The changes in transparency involve most of the cortex of the lens. The changes evolve as follows:
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Hydration of the cortex with development of subcapsular vacuoles.
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Formation of ray-like spaces filled with liquid (morgagnian globules), which is at first transparent and later becomes opaque.
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Lamellar separation of the cortex with development of parallel linear opacities.
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Formation of cuneiform opacities that originate at the periphery of the lens and spread toward the center.
Posterior Subcapsular Opacities
Posterior subcapsular opacities may develop as isolated entities or may be associated with other lens opacities. The opacity begins at the posterior polar region and then spreads toward the periphery. Often, granules and vacuoles are detectable in front of the posterior capsule.
Advanced Cataracts
The crystalline lens may swell and increase in volume because of cortical processes (intumescent cataract). Complete white opacification of the lens is called a mature or morgagnian cataract.
If the liquefied cortical material is not—or is only partially—reabsorbed, the solid nucleus may “sink” to the bottom. Reabsorption of the milky cortex causes a reduction in the lens volume, resulting in capsular folding (hypermature cataract).
Grading of Lens Opacities
Gradations and classifications of cataracts are useful in determining the potential difficulty of cataract surgery, in cataract research, in studies to explore causation, and in trials of putative anticataract drugs. Devices designed to quantify lens opacification have been developed ; these instruments (such as the Kowa Early Cataract Detector and the Scheimpflug photo slit lamp) appear to be more accurate when used to assess the formation of nuclear cataracts than that of cortical cataracts.
A rapid method for the gradation of cataract in epidemiological studies has been reported by Mehra and Minassian ; the area of lenticular opacity is assessed by direct ophthalmoscopy and graded on a scale from 0 to 5. Highly reproducible, validated systems (Lens Opacities Classification System III; see next section) for cataract classification have been developed by Chylack and coworkers to define the effects of specific cataract type and extent very accurately; these enable the effects of specific cataract types on specific visual functions to be quantified.
Lens Opacities Classification System III ( Fig. 5.4.2 )
For nuclear opalescence (NO) or nuclear color (NC), a slit beam is focused on the lens nucleus and the density of the lens is compared with a set of standard photographs. If the density is less than that corresponding to the first photograph, NO or NC is zero or “no nuclear cataract”; if NO or NC is 1, the density is equal to or less than that for the second photograph, and so on. The photographs represent lens nuclei of increasing density, and the patient’s cataract is graded accordingly.
For cortical cataracts (category “C”), a retroillumination (red reflex) view through the dilated pupil is used to view the lens, focused first at the anterior capsule and then at the posterior capsule. The photographs are compared with standard photographs—each succeeding photograph shows the pupillary area covered by more cortical cataract.
For posterior subcapsular cataract (category “P”), a retroillumination (also red reflex) view of the lens is used, focused at the posterior capsule. Again, the patient’s cataract is graded according to standard photographs (see Fig. 5.4.2 ).
Effects of Opacities on Vision
Visual Acuity Reduction
Measurement of visual acuity can remain high despite age-related lens opacities. The severity of the visual disability measured using high-contrast Snellen acuity charts is not sensitive to visual disability characterized by loss of contrast sensitivity.
Usually, visual acuity testing is conducted under ideal circumstances that are not normally met in the real world. Although not a definitive measurement of visual dysfunction, simple Snellen acuity is the most used index to determine whether cataract surgery should be performed. The Preferred Practice Pattern of the American Academy of Ophthalmology recommends Snellen acuity as the best general guide to the appropriateness of surgery but recognizes the need for flexibility with due regard to a patient’s particular functional and visual needs, environment, and risks, which may vary widely.
When the cataract is very dense and opaque, visual acuity may be reduced to light perception only (cataract is still the major cause of blindness throughout the world).
Contrast Sensitivity Reduction
Patients with cataracts commonly complain of loss of the ability to see objects outdoors in bright sunlight and of being blinded easily by approaching headlamps in nighttime driving.
Typically, loss of contrast sensitivity in patients who have cataracts has been reported to be greater at higher spatial frequencies. All cataracts lower contrast sensitivity—the posterior subcapsular opacities have been reported to be the most destructive.
Myopic Shift
The natural aging of the human lens produces a progressive hyperopic shift. Nuclear changes induce a modification of the refractive index of the lens and produce a myopic shift that may be of several diopters or greater. It is possible to predict that an aging person who had emmetropia previously but who can now read with no correction (“second sight”) is developing nuclear cataract. Together with this aging effect goes the loss of the negative asphericity of the lens in youth, balancing the positive asphericity of the natural cornea. The shift to more positive asphericity of the lens with progressive nuclear cataract also reduces visual quality.
If the lens structure becomes heterogeneous, with cortical spoke cataract for example, the change in refractive index may be uneven and may produce some degree of internal irregular astigmatism and disturbance of the higher-order aberrations of Zernike (third order).
Monocular Diplopia
Monocular diplopia is common in patients who have lens opacities, particularly cortical spoke cataract, and in conjunction with water clefts that form radial wedge shapes and contain a fluid of lower refractive index than the surrounding lens. In some cases, patients may complain of polyopia.
Glare
Even minor degrees of lens opacity cause glare because of the forward scatter of light. Such patients often see more poorly in daylight conditions than in the context of night driving. Unlike contrast sensitivity reduction, some glare may be produced by opacities that do not lie within the pupil diameter. The differences between measured visual acuity in a darkened room and acuity in ambient light that produces glare are useful as subjective criteria for the justification of surgery.
Color Shift
The cataractous lens becomes more absorbent at the blue end of the spectrum, especially with nuclear opacities. Usually patients are not aware of this color visual defect until after cataract surgery and visual rehabilitation.
Visual Field Loss
According to the morphology, the density, and the location of the opacities, the field of vision may be affected.
Introduction
The progressive insolubilization of lens protein with age is believed to cause refractive index and density fluctuations, which scatter light and impair vision.
The impact of a patient’s cataract on the retinal image may be appreciated on funduscopic examination, which can show interference with the red reflex and show the blur of fine retinal vessels.
Diagnosis of Lens Opacities
Slit-lamp biomicroscopy is the major method used to observe and assess cataracts. However, the image seen often fails to correlate with the patient’s visual acuity or function. The relationship between alterations in the structural proteins, the increase in light scatter associated with conventional biomicroscopy, and the capacity of visual function is not a simple one. For all lens examinations, the pupil is dilated maximally.
Classification of Lens Opacities
Nuclear Opacities
Initially, an increase in optical density of the nucleus occurs (nuclear sclerosis). The fetal nucleus is first involved and then the whole adult nucleus. The increase in density is followed by an opacification, which implies a change in color, namely from an initial clear to yellow to a subsequent brown (brunescent cataract).
In certain instances, crystals appear in the adult nucleus (or in the cortex, usually posteriorly) that, on slit-lamp examination, appear to be of different colors (polychromatic luster).
Cortical Opacities
The changes in transparency involve most of the cortex of the lens. The changes evolve as follows:
- •
Hydration of the cortex with development of subcapsular vacuoles.
- •
Formation of ray-like spaces filled with liquid (morgagnian globules), which is at first transparent and later becomes opaque.
- •
Lamellar separation of the cortex with development of parallel linear opacities.
- •
Formation of cuneiform opacities that originate at the periphery of the lens and spread toward the center.
Posterior Subcapsular Opacities
Posterior subcapsular opacities may develop as isolated entities or may be associated with other lens opacities. The opacity begins at the posterior polar region and then spreads toward the periphery. Often, granules and vacuoles are detectable in front of the posterior capsule.
Advanced Cataracts
The crystalline lens may swell and increase in volume because of cortical processes (intumescent cataract). Complete white opacification of the lens is called a mature or morgagnian cataract.
If the liquefied cortical material is not—or is only partially—reabsorbed, the solid nucleus may “sink” to the bottom. Reabsorption of the milky cortex causes a reduction in the lens volume, resulting in capsular folding (hypermature cataract).
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