Table 1

Distribution of cases and controls for the variables that were potential risk factors for AK chosen for inclusion in the MV analyses

Variable	Control	Case	Total	OR*	P values	95% CI for OR
Lens disinfectant: classified by the principal active ingredient (PAI)†
1: Polyhexanide (0.00 005–0.0001)	90	11	101	Referent
2: PQ+ALDOX/PQ+Alex‡	26	9	35	2.83	0.038	1.06 to 7.57
3: Hydrogen peroxide 3%	12	5	17	3.41	0.048	1.01 to 11.51
4: Polyquad-1(0.0001%)+polyaminopropyl biguanide	11	2	13	1.49	0.633	0.29 to 7.60
5: Oxipol	55	29	84	4.31	<0.001	2.00 to 9.33
6: Rigid gas permeable lens solution	11	5	16	3.72	0.036	1.09 to 12.71
Unknown	8	2	10
Total	213	63	276
CL materials classification: simplified from the ANSI classification§
Groups I+II+III	18	6	24	1.95	0.233	0.65 to 5.83
Group IV	13	7	20	3.15	0.039	1.06 to 9.37
Group VA	76	13	89	Referent
Groups VB+VC	73	29	102	2.32	0.023	1.12 to 4.81
Rigid gas permeable materials	11	5	16	2.66	0.113	0.79 to 8.91
Unknown	22	3	25
Total	213	63	276
Hygiene score: categories split between the top (worst) quartile of the sample and the rest¶
1: Good–moderate (score 1.75–5.08)	174	30	204	Referent
2: Poor (score 5.09–8.08)	39	33	72	4.91	<0.001	2.68 to 8.98
Total	213	63	276
Hand washing before handling CLs
1: No/unsure	27	21	48	3.71	<0.001	1.90 to 7.22
2: Yes	186	39	225	Referent
Unknown	0	3	3
Total	213	63	276
Showering when wearing CLs
1: No	141	25	166	Referent
2: Yes	72	38	110	2.98	<0.001	1.67 to 5.31
Total	213	63	276
Water activity using CL’s: categories combined
1: None	114	20	134	Referent
2: Ocean/sea/river/lake	42	9	51	1.22	0.649	0.52 to 2.89
3: Public or private pool/hot tub	57	31	88	3.10	0.001	1.63 to 5.91
Unknown	0	3	3
Total	213	63	276
Ethnic group: for categories**
4: British (white)	141	54	195	Referent
6: Other	72	6	78	0.22	0.001	0.09 to 0.53
Unknown	0	3	3
Total	213	63	276
Occupation: for categories††
1–3 Professional/director/manager/associate professional and technical/senior officials	163	36	199	Referent
4–9 Combined	50	22	72	1.99	0.029	1.07 to 3.70
Unknown	0	5	5
Total	213	63	276

*ORs are not adjusted for confounding effects of other variables.
†Classification of CL solutions is given in online supplementary table 2.
‡PAI category 2: PQ +ALDOX/PQ +Alex=Polyquad-1 (0.001%)+ALDOX (0.0005%) or Polyquad-1 (0.0003%)+alexidine (0.00016%)—the latter for 4 controls and 1 case only.
§American National Standard Institute (ANSI) standard Z80.20-2016. American national standard for ophthalmics—contact lenses—standard terminology, tolerances, measurements and physicochemical properties (ophthalmic).
¶Hygiene scores were calculated for the 14 hygiene variables listed in online supplementary table 5 using the rules described in that table. The mean score for each patient was then used to divide the patient sample into a simple binary classification for MV analysis in which the worst quartile (the quartile with the highest score) of the sample was categorised as having “Poor” hygiene and compared with the rest categorised as having “Good-Moderate” hygiene. “Good-Moderate” mean scores were 1-75-5.08 and “Poor” mean scores were 5.09-8.08. Hand washing before handling CLs and showering while wearing CLs were kept as separate variables and and analysed as such.
**Ethnic categories (UK census categories): 1: Asian or Asian British (Bangladeshi, Indian, Pakistani); 2:black or black British (African, Caribbean, other); 4: British (white); 6: other.
††Occupation: 1: managers, directors and senior officials; 2: professional occupations; 3: associate professional and technical occupations; 4: administrative and secretarial occupations; 5: skilled trades occupations; 6: caring, leisure and other service occupations; 7: sales and customer service occupations; 8: process, plant and machine operatives; 9: occupations requiring no specific training or skills and student: categorised by parents’ occupation.
AK, Acanthamoeba keratitis; CL, contact lens; MV, multivariate.