[558]*558Justice Souter
delivered the opinion of the Court.
The question posed is whether, under the Americans with Disabilities Act of 1990 (ADA or Act), 104 Stat. 327, as amended, 42 U. S. C. § 12101 et seq. (1994 ed. and Supp. Ill), an employer who requires as a job qualification that an employee meet an otherwise applicable federal safety regulation must justify enforcing the regulation solely because its standard may be waived in an individual ease. We answer no.
I
In August 1990, petitioner, Albertson’s, Inc., a grocery-store chain with supermarkets in several States, hired respondent, Hallie Kirkingburg, as a truckdriver based at its Portland, Oregon, warehouse. Kirkingburg had more than a decade’s driving experience and performed well when petitioner’s transportation manager took him on a road test.
Before starting work, Kirkingburg was examined to see if he met federal vision standards for commercial truck-drivers. 143 P. 3d 1228, 1230-1231 (CA9 1998). For many decades the Department of Transportation and its predecessors have been responsible for devising these standards for individuals who drive commercial vehicles in interstate commerce.1 Since 1971, the basic vision regulation has required corrected distant visual acuity of at least 20/40 in each eye [559]*559and distant binocular acuity of at least 20/40. See 35 Fed. Reg. 6458, 6463 (1970); 57 Fed. Reg. 6793, 6794 (1992); 49 CFR § 391.41(b)(10) (1998).2 Kirkingburg, however, suffers from amblyopia, an uncorreetable condition that leaves him with 20/200 vision in his left eye and monocular vision in effect.3 Despite Kirkingburg’s weak left eye, the doctor erroneously certified that he met the DOT’S basic vision standards, and Albertson’s hired him.4
In December 1991, Kirkingburg injured himself on the job and took a leave of absence. Before returning to work in November 1992, Kirkingburg went for a further physical as required by the company. This time, the examining physician correctly assessed Kirkingburg’s vision and explained that his eyesight did not meet the basic DOT standards. The physician, or his nurse, told Kirkingburg that in order to be legally qualified to drive, he would have to obtain a waiver of its basic vision standards from the DOT. See 143 [560]*560F. 3d, at 1230; App. 284-285. The doctor was alluding to a scheme begun in July 1992 for giving DOT certification to applicants with deficient vision who had three years of recent experience driving a commercial vehicle without a license suspension or revocation, involvement in a reportable accident in which the applicant was cited for a moving violation, conviction for certain driving-related offenses, citation for certain serious traffic violations, or more than two convictions for any other moving violations. A waiver applicant had to agree to have his vision cheeked annually for deterioration, and to report certain information about his driving experience to the Federal Highway Administration (FHWA or Administration), the agency within the DOT responsible for overseeing the motor carrier safety regulations. See 57 Fed. Reg. 31458, 31460-31461 (1992).5 Kirkingburg applied for a waiver, but because he could not meet the basic DOT vision standard Albertson’s fired him from his job as a truckdriver.6 In early 1993, after he had left Albertson’s, Kirkingburg received a DOT waiver, but Albertson’s refused to rehire him. See 143 F. 3d, at 1231.
Kirkingburg sued Albertson’s, claiming that firing him violated the ADA.7 Albertson’s moved for summary judgment [561]*561solely on the ground that Kirkingburg was "not ‘otherwise qualified’ to perform the job of truck driver with or without reasonable accommodation.” App. 39-40; see id., at 119. The District Court granted the motion, ruling that Albert-son’s had reasonably concluded that Kirkingburg was not qualified without an accommodation because he could not, as admitted, meet the basic DOT vision standards. The court held that giving Kirkingburg time to get a DOT waiver was not a required reasonable accommodation because the waiver program was “a flawed experiment that has not altered the DOT vision requirements.” Id., at 120.
A divided panel of the Ninth Circuit reversed. In addition to pressing its claim that Kirkingburg was not otherwise qualified, Albertson’s for the first time on appeal took the position that it was entitled to summary judgment because Kirkingburg did not have a disability within the meaning of the Act. See id., at 182-185. The Court of Appeals considered but rejected the new argument, concluding that because Kirkingburg had presented “uncontroverted evidence” that his vision was effectively monocular, he had demonstrated that “the manner in which he sees differs significantly from the manner in which most people see.” 143 F. 3d, at 1232. That difference in manner, the court held, was sufficient to establish disability. Ibid.
The Court of Appeals then addressed the ground upon which the District Court had granted summary judgment, acknowledging that Albertson’s consistently required its truekdrivers to meet the DOT’S basic vision standards and that Kirkingburg had not met them (and indeed could not). The court recognized that the ADA allowed Albertson’s to establish a reasonable job-related vision standard as a prerequisite for hiring and that Albertson’s could rely on Government regulations as a basis for setting its standard. The court held, however, that Albertson’s could not use compli[562]*562ance with a Government regulation as the justification for its vision requirement because the waiver program, which Albertson’s disregarded, was “a lawful and legitimate part of the DOT regulatory scheme.” Id., at 1286. The Court of Appeals conceded that Albertson’s was free to set a vision standard different from that mandated by the DOT, but held that under the ADA, Albertson’s would have to justify its independent standard as necessary to prevent ‘“a direct threat to the health or safety of other individuals in the workplace.’” Ibid, (quoting 42 U.S.C. § 12118(b)). Although the court suggested that Albertson’s might be able to make such a showing on remand, 143 F. 3d, at 1236, it ultimately took the position that the company could not, interpreting petitioner’s rejection of DOT waivers as flying in the face of the judgment about safety already embodied in the DOT’s decision to grant them, id., at 1237.
Judge Rymer dissented. She contended that Albertson’s had properly relied on the basic DOT vision standards in refusing to accept waivers because, when Albertson’s fired Kirkingburg, the waiver program did not rest upon “a rule or a regulation with the force of law,” but was merely a way of gathering data to use in deciding whether to refashion the still-applicable vision standards. Id., at 1239.
II
Though we need not speak to the issue whether Kirk-ingburg was an individual with a disability in order to resolve this case, that issue falls within the first question on which we granted certiorari,8 525 U. S. 1064 (1999), and we think it worthwhile to address it briefly in order to correct three missteps the Ninth Circuit made in its discussion of the matter. Under the ADA:
[563]*563“The term ‘disability' means, with respect to an individual—
“(A) a physical or mental impairment that substantially limits one or more of the major life activities of such individual;
“(B) a record of such an impairment; or
“(C) being regarded as having such an impairment.” 42 U.S.C. § 12102(2).
We are concerned only with the first definition.9 There is no dispute either that Kirkingburg’s amblyopia is a physical impairment within the meaning of the Act, see 29 CFR § 1630.2(h)(1) (1998) (defining “physical impairment” as “[a]ny physiological disorder, or condition ... affecting one or more of the following body systems:... special sense organs”), or that seeing is one of his major life activities, see § 16S0.2(i) (giving seeing as an example of a major life activity).10 The question is whether his monocular vision alone “substantially limits” Kirkingburg’s seeing.
In giving its affirmative answer, the Ninth Circuit relied on a regulation issued by the Equal Employment Opportunity Commission (EEOC), defining “substantially limits” as “[significantly restriet[s] as to the condition, manner or duration under which an individual can perform a particular major life activity as compared to the condition, manner, or duration under which the average person in the gen[564]*564eral population can perform that same major life activity.” § 1630.2( j)(ii). The Ninth Circuit concluded that “the manner in which [Kirkingburg] sees differs significantly from the manner in which most people see” because, “[t]o put it in its simplest terms [he] sees using only one eye; most people see using two.” 143 F. 3d, at 1232. The Ninth Circuit majority also relied on a recent Eighth Circuit decision, whose holding it characterized in similar terms: “It was enough to warrant a finding of disability .. . that the plaintiff could see out of only one eye: the manner in which he performed the major life activity of seeing was different.” Ibid. (characterizing Doane v. Omaha, 115 F. 3d 624, 627-628 (1997)).11
But in several respects the Ninth Circuit was too quick to find a disability. First, although the EEOC definition [565]*565of “substantially limits” cited by the Ninth Circuit requires a “significant restriction]” in an individual’s manner of performing a major life activity, the court appeared willing to settle for a mere difference. By transforming “significant restriction” into “difference,” the court undercut the fundamental statutory requirement that only impairments causing “substantial limitations]” in individuals’ ability to perform major life activities constitute disabilities. While the Act “addresses substantial limitations on major life activities, not utter inabilities,” Bragdon v. Abbott, 524 U. S. 624, 641 (1998), it concerns itself only with limitations that are in fact substantial.
Second, the Ninth Circuit appeared to suggest that in gauging whether a monocular individual has a disability a court need not take account of the individual’s ability to compensate for the impairment. The court acknowledged that Kirkingburg’s “brain has developed subconscious mechanisms for coping with [his] visual impairment and thus his body compensates for his disability.” 143 F. 3d, at 1232. But in treating monocularity as itself sufficient to establish disability and in embracing Doane, the Ninth Circuit apparently adopted the view that whether “the individual had learned to compensate for the disability by making subconscious adjustments to the manner in which he sensed depth and perceived peripheral objects,” 143 F. 3d, at 1232, was irrelevant to the determination of disability. See, e. g., Sutton v. United Air Lines, Inc., 130 F. 3d 893, 901, n. 7 (CA101997) (characterizing Doane as standing for the proposition that mitigating measures should be disregarded in assessing disability); EEOC v. Union Pacific R. Co., 6 F. Supp. 2d 1135, 1137 (Idaho 1998) (same). We have just held, however, in Sutton v. United Airlines, Inc., ante, at 482, that mitigating measures must be taken into account in judging whether an individual possesses a disability. We see no principled basis for distinguishing between measures undertaken with artificial aids, like medications and devices, and [566]*566measures undertaken, whether consciously or not, with the body’s own systems.
Finally, and perhaps most significantly, the Court of Appeals did not pay much heed to the statutory obligation to determine the existence of disabilities on a ease-by-ease basis. The Act expresses that mandate clearly by defining “disability” “with respect to an individual,” 42 U. S. C. § 12102(2), and in terms of the impact of an impairment on “such individual,” § 12102(2)(A). See Sutton, ante, at 483; cf. 29 CFR pt. 1630, App. § 1630.2(j) (1998) (“The determination of whether an individual has a disability is not necessarily based on the name or diagnosis of the impairment the person has, but rather on the effect of that impairment on the life of the individual”); ibid. (“The determination of whether an individual is substantially limited in a major life activity must be made on a case by case basis”). While some impairments may invariably cause a substantial limitation of a major life activity, cf. Bragdon, supra, at 642 (declining to address whether HIV infection is a per se disability), we cannot say that monocularity does. That category, as we understand it, may embrace a group whose members vary by the degree of visual acuity in the weaker eye, the age at which they suffered their vision loss, the extent of their compensating adjustments in visual techniques, and the ultimate scope of the restrictions on their visual abilities. These variables are not the stuff of a per se rule. While monocularity inevitably leads to some loss of horizontal field of vision and depth perception,12 consequences the Ninth [567]*567Circuit mentioned, see 143 F. 3d, at 1232, the court did not identify the degree of loss suffered by Kirkingburg, nor are we aware of any evidence in the record specifying the extent of his visual restrictions.
This is not to suggest that monocular individuals have an onerous burden in trying to show that they are disabled. On the contrary, our brief examination of some of the medical literature leaves us sharing the Government’s judgment that people with monocular vision “ordinarily” will meet the Act’s definition of disability, Brief for United States et al. as Amici Curiae 11, and we suppose that defendant companies will often not contest the issue. We simply hold that the Act requires monocular individuals, like others claiming the Act’s protection, to prove a disability by offering evidence that the extent of the limitation in terms of their own experience, as in loss of depth perception and visual field, is substantial.
III
Petitioner’s primary contention is that even if Kirkingburg was disabled, he was not a “qualified” individual with a disability, see 42 U. S. C. § 12112(a), because Albertson’s merely insisted on the minimum level of visual acuity set forth in the DOT’S Motor Carrier Safety Regulations, 49 CFR § 391.41 (b)(10) (1998). If Albertson’s was entitled to enforce that standard as defining an “essential job functio[n] of the employment position,” see 42 U. S. C. § 12111(8), that is the end of the case, for Kirkingburg concededly could not satisfy it.13
[568]*568Under Title I of the ADA, employers may justify their use of “qualification standards . . . that screen out or tend to screen out or otherwise deny a job or benefit to an individual with a disability,” so long as such standards are “job-related and consistent with business necessity, and ... performance cannot be accomplished by reasonable accommodation ... § 12113(a). See also § 12112(b)(6) (defining discrimination to include “using qualification standards ... that screen out or tend to screen out an individual with a disability ... unless the standard ... is shown to be job-related for the position in question and is consistent with business necessity").14
Kirkingburg and the Government argue that these provisions do not authorize an employer to follow even a facially applicable regulatory standard subject to waiver without making some enquiry beyond determining whether the applicant or employee meets that standard, yes or no. Before an employer may insist on compliance, they say, the employer must make a showing with reference to the particular job that the waivable regulatory standard is “job-related ... and ... consistent with business necessity,” see § 12112(b)(6), and that after consideration of the capabilities of the individual a reasonable accommodation could not fairly resolve the competing interests when an applicant or employee cannot wholly satisfy an otherwise justifiable job qualification.
[569]*569The Government extends this argument by reference to a further section of the statute, which at first blush appears to be a permissive provision for the employer’s and the public’s benefit. An employer may impose as a qualification standard “a requirement that an individual shall not pose a direct threat to the health or safety of other individuals in the workplace,” § 12118(b), with “direct threat” being defined by the Act as “a significant risk to the health or safety of others that cannot be eliminated by reasonable accommodation,” § 12111(3); see also 29 CFR § 1630.2(r) (1998). The Government urges us to read subsections (a) and (b) together to mean that when an employer would impose any safety qualification standard, however specific, tending to screen out individuals with disabilities, the application of the requirement must satisfy the ADA’s “direct threat” criterion, see Brief for United States et al. as Amici Curiae 22. That criterion ordinarily requires “an individualized assessment of the individual’s present ability to safely perform the essential functions of the job,” 29 CFR §1630.2(r) (1998), '‘based on medical or other objective evidence,” Bragdon, 524 U. S., at 649 (citing School Bd. of Nassau Cty. v. Arline, 480 U. S. 273, 288 (1987)); see 29 CFR §1630.2(r) (1998) (assessment of direct threat “shall be based on a reasonable medical judgment that relies on the most current medical knowledge and/or on the best available objective evidence”).15
[570]*570Albertson’s answers essentially that even assuming the Government has proposed a sound reading of the statute for the general run of eases, this ease is not in the general run. It is crucial to its position that Albertson’s here was not insisting upon a job qualification merely of its own devising, subject to possible questions about genuine appropriateness and justifiable application to an individual for whom some accommodation may be reasonable. The job qualification it was applying was the distant visual acuity standard of the Federal Motor Carrier Safety Regulations, 49 CFR §391.41(b)(10) (1998), which is made binding on Albertson’s by §391.11: “[A] motor carrier shall not... permit a person to drive a commercial motor vehicle unless that person is qualified to drive,” by, among other things, meeting the physical qualification standards set forth in §391.41. The validity of these regulations is unchallenged, they have the force of law, and they contain no qualifying language about individualized determinations.
If we looked no further, there would be no basis to question petitioner’s unconditional obligation to follow the regulations and its consequent right to do so. This, indeed, was the understanding of Congress when it enacted the ADA, see infra, at 573-574.16 But there is more: the waiver program.
The Court of Appeals majority concluded that the waiver program “precludes [employers] from declaring that persons determined by DOT to be capable of performing the job of commercial truck driver are incapable of performing that job by virtue of their disability,” and that in the face of a waiver [571]*571an employer “will not be able to avoid the [ADA’s] strictures by showing that its standards are necessary to prevent a direct safety threat,” 143 F. 3d, at 1237. The Court of Appeals thus assumed that the regulatory provisions for the waiver program had to be treated as being on par with the basic visual acuity regulation, as if the general rule had been modified by some different safety standard made applicable by grant of a waiver. Cf. Conroy v. Aniskoff, 507 U. S. 511, 515 (1993) (noting the “ ‘cardinal rule that a statute is to be read as a whole’” (quoting King v. St Vincent’s Hospital, 502 U. S. 215, 221 (1991))). On this reading, an individualized determination under a different substantive safety rule was an element of the regulatory regime, which would easily fit with any requirement of 42 U. S. C. §§ 12113(a) and (b) to consider reasonable accommodation. An employer resting solely on the federal standard for its visual acuity qualification would be required to accept a waiver once obtained, and probably to provide an applicant some opportunity to obtain a waiver whenever that was reasonably possible. If this was sound analysis, the District Court’s summary judgment for Albertson’s was error.
But the reasoning underlying the Court of Appeals’s decision was unsound, for we think it was error to read the regulations establishing the waiver program as modifying the content of the basic visual acuity standard in a way that dis-entitled an employer like Albertson’s to insist on it. To be sure, this is not immediately apparent. If one starts with the statutory provisions authorizing regulations by the DOT as they stood at the time the DOT began the waiver program, one would reasonably presume that the general regulatory standard and the regulatory waiver standard ought to be accorded equal substantive significance, so that the content of any general regulation would as a matter of law be deemed modified by the terms of any waiver standard thus applied to it. Compare 49 U. S. C. App. § 2505(a)(3) (1988 ed.) (“Such regulation shall... ensure that... the physical [572]*572condition of operators of commercial motor vehicles is adequate to enable them to operate the vehicles safely”),17 with 49 U. S. C. App. § 2505(f) (1988 ed.) (“After notice and an opportunity for comment, the Secretary may waive, in whole or in part, application of any regulation issued under this section with respect to any person or class of persons if the Secretary determines that such waiver is not contrary to the public interest and is consistent with the safe operation of commercial motor vehicles”).18 Safe operation is supposed to be the touchstone of regulation in each instance.
As to the general visual acuity regulations in force under the former provision,19 affirmative determinations that the selected standards were needed for safe operation were indeed the predicates of the DOT action. Starting in 1937, the federal agencies authorized to regulate commercial motor vehicle safety set increasingly rigorous visual acuity standards, culminating in the current one, which has remained unchanged since it became effective in 1971.20 When [573]*573the FHWA proposed it, the agency found that “[a]ccident experience in recent years has demonstrated that reduction of the effects of organic and physical disorders, emotional impairments, and other limitations of the good health of drivers are increasingly important factors in accident prevention,” 34 Fed. Reg. 9080, 9081 (1969) (Notice of Proposed Rule Making); the current standard was adopted to reflect the agency’s conclusion that “drivers of modern, more complex vehicles” must be able to “withstand the increased physical and mental demands that their occupation now imposes.” 35 Fed. Reg. 6458 (1970). Given these findings and “in the light of discussions with the Administration’s medieal advisers,” id., at 6459, the FHWA made a considered determination about the level of visual acuity needed for safe operation of commercial motor vehicles in interstate commerce, an “area [in which] the risks involved are so well known and so serious as to dictate the utmost caution.” Id., at 17419.
For several reasons, one would expect any regulation governing a waiver program to establish a comparable substantive standard (albeit for exceptional cases), grounded on known facts indicating at least that safe operation would not be jeopardized. First, of course, safe operation was the criterion of the statute authorizing an administrative waiver scheme, as noted already. Second, the impetus to develop a waiver program was a concern that the existing substantive standard might be more demanding than safety required. When Congress enacted the ADA, it recognized that federal safety rules would limit application of the ADA as a matter of law. The Senate Labor and Human Resources Committee Report on the ADA stated that “a person with a disability applying for or currently holding a job subject to [DOT standards for drivers] must be able to satisfy these physical qualification standards in order to be considered a qualified individual with a disability under title I of this legislation.” [574]*574S. Rep. No. 101-116, pp. 27-28 (1998). The two primary House Committees shared this understanding, see H. R. Rep. No. 101-485, pt. 2, p. 57 (1990) (House Education and Labor Committee Report); id., pt. 3, at 34 (House Judiciary Committee Report). Accordingly, two of these Committees asked “the Secretary of Transportation [to] undertake a thorough review’’ of current knowledge about the capabilities of individuals with disabilities and available technological aids and devices, and make “any necessary changes” within two years of the enactment of the ADA. S. Rep. No. 101-116, at 27-28; see H. R. Rep. No. 101-485, pt. 2, at 57; see also id., pt. 3, at 34 (expressing the expectation that the Secretary of Transportation would “review these requirements to determine whether they are valid under this Act”). Finally, when the FHWA instituted the waiver program it addressed the statutory mandate by stating in its notice of final disposition that the scheme would be “consistent with the safe operation of commercial motor vehicles,” just as 49 U. S. C. App. § 2505(f) (1988 ed.) required, 57 Fed. Reg. 31460 (1992).
And yet, despite this background, the regulations establishing the waiver program did not modify the general visual acuity standards. It is not that the waiver regulations failed to do so in a merely formal sense, as by turning waiver decisions on driving records, not sight requirements. The FHWA in fact made it clear that it had no evidentiary basis for concluding that the pre-existing standards could be lowered consistently with public safety. When, in 1992, the FHWA published an “[a]dvance notice of proposed rule-making” requesting comments “on the need, if any, to amend its driver qualification requirements relating to the vision standard,” id., at 6793, it candidly proposed its waiver scheme as simply a means of obtaining information bearing on the justifiability of revising the binding standards already in place, see id., at 10295. The agency explained that the “object of the waiver program is to provide objective data [575]*575to be considered in relation to a rulemaking exploring the feasibility of relaxing the current absolute vision standards in 49 CFR part 391 in favor of a more individualized standard.” Ibid. As proposed, therefore, there was not only no change in the unconditional acuity standards, but .no indication even that the FHWA then had a basis in fact to believe anything more lenient would be consistent with public safety as a general matter. After a bumpy stretch of administrative procedure, see Advocates for Highway and Auto Safety v. FHWA, 28 F. 3d 1288, 1290 (CADC 1994), the FHWA’s final disposition explained again that the waivers were proposed as a way to gather facts going to the wisdom of changing the existing law. The waiver program “will enable the FHWA to conduct a study comparing a group of experienced, visually deficient drivers with a control group of experienced drivers who meet the current Federal vision requirements. This study will provide the empirical data necessary to evaluate the relationships between specific visual deficiencies and the operation of [commercial motor vehicles]. The data will permit the FHWA to properly evaluate its current vision requirement in the context of actual driver performance, and, if necessary, establish a new vision requirement which is safe, fair, and rationally related to the latest medical knowledge and highway technology.” 57 Fed. Reg. 31458 (1992). And if all this were not enough to show that the FHWA was planning to give waivers solely to collect information, it acknowledged that a study it had commissioned had done no more than “ ‘illuminat[e] the lack of empirical data to establish a link between vision disorders and commercial motor vehicle safety,’” and “‘failed to provide a sufficient foundation on which to propose a satisfactory vision standard for drivers of [commercial motor vehicles] in interstate commerce,’ ” Advocates for Highway and Auto Safety, supra, at 1293 (quoting 57 Fed. Reg. 31458 (1992)).
[576]*576In sum, the regulatory record made it plain that the waiver regulation did not rest on any final, factual conclusion that the waiver scheme would be conducive to public safety in the manner of the general acuity standards and did not purport to modify the substantive content of the general acuity regulation in any way. The waiver program was simply an experiment with safety, however well intended, resting on a hypothesis whose confirmation or refutation in practice would provide a factual basis for reconsidering the existing standards.21
[577]*577Nothing in the waiver regulation, of course, required an employer of commercial drivers to accept the hypothesis and participate in the Government’s experiment. The only question, then, is whether the ADA should be read to require such an employer to defend a decision to decline the experiment. Is it reasonable, that is, to read the ADA as requiring an employer like Albertson’s to shoulder the general statutory burden to justify a job qualification that would tend to exclude the disabled, whenever the employer chooses to abide by the otherwise clearly applicable, unamended substantive regulatory standard despite the Government’s willingness to waive it experimentally and without any finding of its being inappropriate? If the answer were yes, an employer would in fact have an obligation of which we can think of no comparable example in our law. The employer would be required in effect to justify de novo an existing and otherwise applicable safety regulation issued by the Government itself. The employer would be required on a ease-by-ease basis to reinvent the Government’s own wheel when the Government had merely begun an experiment to provide data to consider changing the underlying specifications. And what is even more, the employer would be required to do so when the Government had made an affirmative record indicating that contemporary empirical evidence was hard to come by. It is simply not credible that Congress enacted the ADA (before there was any waiver program) with the understanding that employers choosing to respect the Government’s sole substantive visual acuity regulation in the [578]*578face of an experimental waiver might be burdened with an obligation to defend the regulation’s application according to its own terms.
The judgment of the Ninth Circuit is accordingly reversed.
It is so ordered.
Justice Stevens and Justice Breyer join Parts I and III of this opinion.