Larry J. Davis

Characterization of ocular surface symptoms from optometric practices in North America.

Purpose. This study characterized ocular symptoms typical of dry eye in an unselected optometric clinical population in the United States and Canada. Methods. Self-administered dry eye questionnaires, one for non–contact lens wearers (dry eye questionnaire) and one for contact lens wearers (contact lens dry eye questionnaire), were completed at six clinical sites in North America. Both questionnaires included categoric scales to measure the prevalence, frequency, diurnal severity, and intrusiveness of nine ocular surface symptoms. The questionnaires also asked how much these ocular symptoms affected daily activities and contained questions about computer use, medications, and allergies. The examining doctors, who were masked to questionnaire responses, recorded a nondirected dry eye diagnosis for each patient, based on their own diagnostic criteria. Results. The dry eye questionnaires were completed by 1,054 patients. The most common ocular symptom was discomfort, with 64% of non–contact lens wearers and 79% of contact lens wearers reporting the symptom at least infrequently. There was a diurnal increase in the intensity of many symptoms, with symptoms such as discomfort, dryness, and visual changes reported to be more intense in the evening. The 22% percent of non–contact lens wearers and 15% of contact lens wearers diagnosed with dry eye (most in the mild to moderate categories) reported symptoms at a greater frequency than those not diagnosed with dry eye. Conclusions. Our results show that symptoms of ocular irritation and visual disturbances were relatively common in this unselected clinical population. The intensity of many ocular symptoms increased late in the day, which suggested that environmental factors played a role in the etiology of the symptoms.

Longitudinal changes in corneal curvature in keratoconus.

Purpose: This study was designed to identify factors that predict longitudinal increases in corneal curvature as measured by the First Definite Apical Clearance Lens (FDACL) and flatter keratometric reading (Flat K) in keratoconus. Methods: The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a long-te rm evaluation of the natural history of keratoconus involving 1209 patients. This report uses 8 years of follow-up data from 1032 patients who had penetrating keratoplasty in neither eye at baseline and who provided enough data to compute the slope of the change with time in the FDACL or the Flat K. Outcome measures included the aforementioned slopes and whether the FDACL or the Flat K increased by 3.00 or more diopters (D) in at least 1 eye. Results: At CLEK Study entry, patients were aged 38.9 ± 10.8 years. Overall, 44.3% of them were women, and 69.3% of them were white. The slope of the change in FDACL (0.18 ± 0.60 D/y) and Flat K (0.20 ± 0.80 D) during 8 years translates into expected 8-year increases of 1.44 D in FDACL and 1.60 D in Flat K. Increases of ≥3.00 D in either eye had an 8-year incidence of 24.8% for FDACL and 24.1% for Flat K. Independent predictors of increased FDACL included younger age, poorer baseline high-contrast manifest refraction visual acuity, and non-white race. Younger age and poorer high-contrast manifest refraction visual acuity were independent predictors of a >3.00-D increase for both FDACL and Flat K. Conclusion: CLEK patients exhibited a slow but clear increase in corneal curvature. Younger age and poorer high-contrast manifest refraction visual acuity at baseline predicted the rate of change in corneal curvature.

Repeatability of subjective refraction in myopic and keratoconic subjects: results of vector analysis

This paper evaluates the repeatability of refraction in keratoconus patients and normal myopes, using representations of spherocylindrical power that are theoretically valid. Data consist of test–retest refraction data from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study and similar data from normal myopes. Dioptric powers are transformed to an orthogonal vector representation of dioptric power. The metric of change is the dioptric difference between test and retest. The median difference between test and retest in keratoconus patients is four to six times larger than in normal myopes. Refraction over a rigid contact lens on a keratoconic cornea improves repeatability but remains approximately twice as large as in normal myopes. The methods demonstrated here possess advantages over previous methods and provide a more valid comparison between test and retest and between different subject groups. The repeatability of refraction in keratoconus patients is substantially worse than in normal myopes.

Standardized rigid contact lens fitting protocol for keratoconus

Keratoconus is typically managed by a variety of rigid contact lens fitting techniques and lens designs. The two most fundamental fitting techniques are apical corneal touch (including divided or three-point touch) and apical clearance. In the course of designing a multi-center study of keratoconus patients, a standardized keratoconus fitting protocol was developed. All contact lens parameter options are uniform except for base curve and secondary curve radii, which are determined by interpretation of fluorescein patterns using the CLEK Study trial lens set and protocol. The initial trial lenss base curve is the average keratometric reading; sequentially steeper lenses are applied until definite apical clearance is observed. We have evaluated the feasibility of this standardized fitting protocol on 30 keratoconus patients. Our results suggest that we have developed a standardized contact lens fitting set and fitting protocol to simplify contact lens management in patients with mild to moderate keratoconus.

Visual Acuity Repeatability in Keratoconus: Impact on Sample Size

Purpose. The purpose of this paper is to determine the repeatability of visual acuity measurement in keratoconus and to describe the impact of measurement repeatability on sample size. Methods. Approximately 10% of a 1209 patient sample in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study were selected randomly for a Repeat CLEK Study Visit. Patients were tested at the 15 CLEK Participating Clinics. The test-retest sample consisted of 134 keratoconus patients who met the entry criteria of the CLEK Study. High and low contrast Bailey-Lovie visual acuity was measured with the patients habitual visual correction (entrance visual acuity monocularly and binocularly), and with the best correction monocularly (either the patients rigid contact lens and over-refraction, or with a CLEK Study trial lens and appropriate over-refraction) at two visits separated by a median of 90 days (range 22 to 268 days). Results. The mean absolute differences between the number of letters correct at the two visits ranged from a low of 3.24 ± 3.1 for entrance high contrast binocular acuity to a high of 5.48 ± 5.1 for best corrected low contrast monocular acuity. Intraclass correlation coefficients ranged from 0.757 to 0.853. The visual acuity score was somewhat higher at the Repeat Visit than at the Baseline Visit when the examiners were different between visits. Conclusions. Given the variable vision reported by keratoconus patients, visual acuity in this sample was very repeatable. Repeatability was slightly poorer when different examiners tested visual acuity at the Baseline and Repeat Visits.

Repeatability of Refraction and Corrected Visual Acuity in Keratoconus

Purpose. The purpose of the test‐retest phase of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study was to determine the repeatability of the various parts of the CLEK Study protocol. This paper presents the test‐retest parameters of the refraction protocol. Methods. We examined 138 CLEK Study‐eligible patients on two occasions (median, 90 days; range, 22 to 268 days). All patients underwent subjective refraction on two occasions, and contact lens over‐refractions were performed either over the patients habitual rigid contact lenses or over a trial rigid contact lens equal in base curve to the steep keratometric reading in nonrigid contact lens wearers. Results. Mean interoccasion differences ± SD were ‐0.32 ± 2.91 D and ‐0.17 ± 1.39 D for subjective refraction sphere and cylinder power, respectively, and the mean absolute difference for subjective refraction cylinder axis was 18.1 ± 20.2°. The mean interoccasion difference ± SD for high‐contrast visual acuity with subjective refraction was 0.38 ± 10.9 letters correct. Mean interoccasion differences ± SD were ‐0.11 ± 0.81 D and 0.02 ± 0.67 D for contact lens over‐refraction sphere and cylinder power, respectively, and the mean absolute difference for contact lens over‐refraction cylinder axis was 11.6 ± 9.9°. The mean interoccasion difference ± SD for visual acuity with contact lens over‐refraction was 0.50 ± 5.2 letters correct and 0.71 ± 6.9 letters correct for high‐ and low‐contrast visual acuity, respectively. Conclusions. The repeatability of subjective refraction in keratoconus patients is good but somewhat lower than that found in nondiseased eyes. Only 36% of our repeat measures of sphere power from subjective refraction fell within 0.50 D of each other, compared with more than 90% in studies of normal eyes. (Optom Vis Sci 1998;75:887–896)

Complex refractive errors in pediatric patients: cause, management, and criteria for success.

Background. Uncorrected refractive error in children is an important contributor to permanent neurological visual impairment (amblyopia). Spectacles are often inadequate for certain refractive errors that occur in the pediatric population. Therefore, the purpose of this paper is to present the diagnostic and therapeutic considerations of infants and children referred to a hospital specialty contact lens practice during a 30-month period. Methods. A retrospective cohort design was used to study patients 12 years or younger referred to a hospital-based contact lens service and cared for by the author. Sixty patients were first examined during the enrollment period. Follow-up data were collected after a period of no less than 3 years from the initial visit. Success with the prescribed therapy was assessed by comparing the final method of optical correction with that prescribed at the initial presentation. Results. Aphakia and trauma were the two most common causes for referral, representing 57% of the patients younger than age 12. Contact lenses were prescribed for 51 of the 60 patients (85 %) at presentation. Seventy-five percent of patients with unilateral aphakia attributable to congenital cataract were wearing a contact lens at the most recent follow-up examination. This was reduced to 60% with aphakia after trauma and just 50% with bilateral aphakia. The frequency of a visual acuity of 20/40 or better was 67% for bilateral aphakia, 47% after trauma with aphakia, and 25% for unilateral aphakia. Conclusions. The results presented here suggest that patients with unilateral aphakia attributable to congenital cataract have the most consistent contact lens wear, followed by patients with unilateral aphakia attributable to trauma. Patients with bilateral aphakia were more likely to have changed to spectacle lens wear. Patients wearing contact lenses at the most recent follow-up examination were more likely to have good visual acuity.

Feasibility of fitting contact lenses with apical clearance in keratoconus.

ABSTRACT Despite the wide variety of rigid contact lens fitting philosophies for the visual correction of keratoconus, questions remain, including which approach—flat, divided support, or steep—contributes the most toward the preservation of a clear cornea. One goal of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Pilot Study was to determine the feasibility of managing early keratoconus patients with apical clearance rigid contact lenses. Of 30 keratoconus patients identified with at least 1 nonscarred cornea, 17 patients (30 eyes) were randomly assigned to a steep lens fitting protocol. After trial fitting with a standardized lens design demonstrating minimum apical clearance, lenses were dispensed whose base curve was 0.2 mm steeper than the minimum apical clearance lens. Patients were re-evaluated on a quarterly schedule concluding at 12 months. Changes in keratometry between baseline and 12 months identified unequal steepening of the flat and steep corneal curvatures, suggestive of corneal molding. Best corrected rigid lens visual acuity measures illustrated no significant changes over the course of the study. Clinically significant corneal compromise pleting the pilot study and fitted with apical clearance developed mild corneal scarring.

Transient rigid lens-induced striae in keratoconus.

We have observed spontaneous development of striae and an enhanced visibility of them after placing rigid gas permeable contact lenses on six patients suspected of having early keratoconus. These fine folds subside upon removal of the rigid lens. This observation assists clinicians with the differential diagnosis of irregular astigmatism when the definitive biomicroscopic signs of keratoconus are either not present or are so subtle that their presence is questionable. Although these striae may not occur in all patients suspected of having early keratoconus, we find that observation of the posterior cornea in the presence of a rigid lens will often confirm the diagnosis of keratoconus. We have not seen similar striae in patients whose clinical presentation is not consistent with early keratoconus.