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Biomedical subjects

S J Doyle

Publications and source records attributed to S J Doyle.

12 recordsLinked to original sources
PubMed1998

Epithelial debridement for secondary hyperopia following myopic excimer laser photorefractive keratectomy.

BACKGROUND: To evaluate epithelial debridement for the treatment of persistent hyperopia in eyes that had photorefractive keratectomy (PRK). SETTING: Optimax Laser Eye Clinics, Manchester, London, Bristol, England. METHODS: Epithelial debridement was performed on 46 eyes to reduce the hypermetropia following excimer laser PRK. RESULTS: Mean age of the patients was 43 years +/- 9.7 (SD). Mean refractive change was -0.51 diopter (D) +/- 0.76 (range +0.75 to -2.50 D). Mean change in best corrected visual acuity (BCVA) was 0.00 Logmar units (range +0.40 to -0.20 units), although 33% of eyes lost one line or more of Logmar BCVA. Mean follow-up after debridement was 61.0 +/- 26.9 weeks (range 26 to 140 weeks). CONCLUSIONS: Epithelial debridement is an unpredictable procedure to treat secondary hyperopia after PRK, producing a small mean change in spherical equivalent with a wide range of results. A significant number of eyes lost one line or more of Logmar BCVA. We therefore do not advocate epithelial debridement after PRK.

Adult↗
PubMed1998

Emmetropisation, axial length, and corneal topography in teenagers with Down's syndrome.

AIM: To study the refractive status and corneal topography in Down's syndrome. METHOD: A matched cohort subgroup of 50 individuals with Down's syndrome in the Manchester area aged 15-22 years was studied by refraction, corneal topography, A-scan biometry, slit lamp examination, and orthoptic examination. RESULTS: (1) A linear relation was found between axial length and spherical equivalent refraction. There was no statistical relation between keratometry and the axial length. (2) 80% of the group had a hyperopic refraction (mean +2.46 D, range +0.5 to +7.5 D); 18% were myopic (mean -2.75 D, range -0.5 to -8.0 D); and 2% were emmetropic (within plus or minus 0.5 D of zero). The overall mean spherical equivalent refraction was +1.43 (SD 2.86) D. 63% of eyes could see 6/12 or better and 66% of the individuals had a binocular vision of 6/12 or better. (3) Corneal topography was generally of a regular "bow tie" pattern, but there was a high incidence of oblique cylinders. Mean cylinder strength was 1.14 (1.15) D. (4) The prevalence of overt keratoconus was 2%. 6% had corneal topography with inferior steepening which may be a preclinical keratoconic process. CONCLUSIONS: In this cohort of late teenagers with Down's syndrome, emmetropisation has failed to occur in most individuals. In a similar aged group of non-disabled individuals one would expect about 83% emmetropic (plus or minus 0.25 D), 13% myopic, and 4% hyperopic. The wide spread of oblique cylinders and the small proportion of with the rule astigmatism is probably related to this failure of emmetropisation. The prevalence of 2% keratoconus in Down's syndrome compares with that found by other authors of between 5.5 and 15%. The 6% with inferior steepening on topography will be followed up over the next few years to see if there is any development of clinical keratoconus. Hence we will see if corneal topography is useful as a screening tool for preclinical keratoconus in this high risk group.

Adolescent↗
PubMed1998

Comparison of 18% ethanol and mechanical debridement for epithelial removal before photorefractive keratectomy.

PURPOSE: To assess the safety of alcohol compared to mechanical debridement for epithelial removal prior to photorefractive keratectomy (PRK). METHODS: Forty-one second eyes of 41 patients underwent epithelial removal using alcohol prior to PRK with a Nidek EC-5000 excimer laser. The results were compared with the results of the 41 first eyes of the same patients that had mechanical debridement. RESULTS: Initial results showed that the alcohol treated group tended to stay slightly hyperopic but had less haze compared to the mechanical debridement group. The treating surgeons favored alcohol as the preferred method of epithelium removal. CONCLUSION: Alcohol debridement is an effective procedure although algorithms may have to be altered to take into account the slightly different healing process postoperatively.

Debridement↗
PubMed1997

Results of excimer laser retreatment of residual myopia after previous photorefractive keratectomy.

BACKGROUND: Nine percent to 30% of all patients who undergo a single excimer laser photorefractive keratectomy (PRK) do not achieve an unaided visual acuity of 20/ 40 or better and may require optical correction to obtain adequate vision. METHODS: The authors performed a retrospective analysis of the records of 164 patients who had undergone retreatment with the excimer laser for residual myopia after a previous PRK. Mean follow-up was 35.5 +/- 15.2 weeks (range, 26-104 weeks). RESULTS: The mean spherical equivalent (MSE) before retreatment was -2.59 +/- 1.36 diopter (D) (range, -0.50 to -7.75 D). The final MSE after reablation was -0.52 +/- 1.36 D (range, 2.50 to -5.50). Of the 164 patients, 107 (65.2%) obtained a final refraction within 1.00 D of emmetropia and 111 (67.3%) achieved an unaided visual acuity of 20/40 or better. Only 10 patients (6.1%) lost more than one Snellen line of best-corrected visual acuity. The final MSE result for the subgroup of patients who had a pre-retreatment myopia of between -0.50 and -1.90 D (-0.31 +/- 1.09 D) was significantly closer to emmetropia than that of the subgroup with a residual myopia of -4.00 to -7.75 D (-1.62 +/- 1.94 D). CONCLUSIONS: Excimer laser retreatment may provide a relatively safe and predictable method of correcting residual myopia after an earlier PRK with a 25% extra correction recommended for residual myopia.

Adult↗
PubMed1997

Astigmatism induced by spherical photorefractive keratectomy corrections.

PURPOSE: The purpose of the study is to evaluate the induced astigmatism after spherical photorefractive keratectomy on the Summit Omnimed (Summit Instruments, Waltham, MA) and the Nidek EC-5000 (Nidek Co. Ltd, Aichi, Japan) excimer lasers. METHODS: A total of 4269 eyes of 3289 patients were treated with a 5-mm optical zone using the Summit Omnimed excimer laser and 1825 eyes of 1303 patients treated with the Nidek EC-5000 excimer laser. The final astigmatic refractive outcome was compared with the initial refraction by vector analysis (Alpin and Jaffe method). RESULTS: Subjective astigmatic refraction for the Summit laser reduced from a mean of -0.39 diopter (D) +/- standard deviation (SD) 0.33 D (range, 0 to -2.50 D) to -0.33 D +/- SD 0.41 D (range, 0 to -3.00 D). Surgically induced astigmatism (SIA) had a mean of 0.42 +/- SD 0.34 D (range, 0 to 2.89 D). Mean SIA increased with increasing preoperative astigmatism by 0.60 D SIA for every 1.00 D of preoperative cylinder. For the Nidek laser, subjective astigmatic refraction changed from a mean of -0.18 D +/- SD 0.21 D (range, 0 to -1.25 D) to -0.30 D +/- SD 0.33 D (range, 0 to -3.00 D). Surgically induced astigmatism had a mean of -0.32 D +/- SD 0.29 (range, 0 to 3.05 D). Mean SIA increased with increasing preoperative astigmatism by 0.47 D SIA for every 1.00 D of preoperative cylinder. CONCLUSIONS: The authors show that spherical photorefractive keratectomy corrections can induce significant astigmatic change, particularly if a large amount of preoperative astigmatism is present.

Astigmatism↗
PubMed1997

Reduction in intraocular pressure after excimer laser photorefractive keratectomy. Correlation with pretreatment myopia.

PURPOSE: The authors relate the observed reduction in intraocular pressure (IOP) after excimer laser treatment to the degree of myopia treated. BACKGROUND: Intraocular pressure, measured by both Goldmann applanation and noncontact tonometry, has been reported to decrease after excimer laser photorefractive keratectomy (PRK). However, IOP readings after excimer laser PRK might be inaccurate as a consequence of changes in both the thickness and curvature of the cornea. METHODS: Baseline IOP readings were measured by noncontact tonometry in each eye of a group of 1320 patients at the time of their initial consultation. These were compared to readings obtained before treatment of the second eye, which took place a minimum of 4 months later. The untreated eyes served as controls. The paired Student's t test was used for statistical analysis. RESULTS: After PRK, a decrease was observed in the IOP of treated eyes that was related to the degree of myopia treated. A significant difference was observed between treated and untreated eyes (P < 0.0000). CONCLUSIONS: The IOP measured after PRK for myopia may be reduced because of changes in corneal thickness (absence of Bowman's membrane and central thinning) and topography. This is of particular relevance when monitoring the IOP of those patients who are given steroid drops to prevent regression. It also may be of importance in the management of any future glaucoma.

Adult↗
PubMed1997

Corneal temperature changes during photorefractive keratectomy.

PURPOSE: Corneal temperature changes in photorefractive keratectomy (PRK) have been implicated in the aetiology of subepithelial haze. This study was undertaken to quantify the temperature change during this surgical procedure. METHODS: Non-contact, colour-coded ocular thermography was performed by using an infrared detection system during PRK on a group of 12 subjects. RESULTS: Mean (+/-SD) central ocular surface temperature (OST) after epithelial debridement was 29.15 +/- 0.39 degrees C. Mean peak OST during PRK was 37.77 +/- 0.67 degrees C, with most of the temperature increase occurring during the first 15 s. Factors such as ablation depth, optical correction, and procedure duration were not demonstrated to have a significant effect on corneal temperature during the procedure, suggesting a complex relation between-PRK parameters and the change in corneal temperature. CONCLUSIONS: Previous work suggested that corneal collagen denatures at approximately 39 degrees C, and it has been demonstrated that corneal temperature may be elevated to this level during routine PRK. Further research is indicated into the effects of preoperative cooling and pausing in treatment to reduce temperature changes.

Collagen↗
PubMed1996

PRK in patients with a keratoconic topography picture. The concept of a physiological 'displaced apex syndrome'.

AIMS/BACKGROUND: Keratoconus is generally held to be an absolute contraindication for photorefractive keratectomy (PRK). Corneas with inferior steepening on corneal topography are widely thought to have subclinical keratoconus. We were not convinced that this is always the case, as there seems to be a group of patients with a stable inferior steepening pattern on topography who show no other characteristics of clinical keratoconus. We thus decided to offer PRK to some of these patients under strictly defined criteria. METHOD: Four myopic patients with a topography pattern of inferior steepening were submitted to PRK. They were selected on the basis of being aged over 35, with a stable refraction, no slit-lamp signs of keratoconus, and a corrected vision of not less than 6/7 (0.9) with a spherical spectacle correction. They gave fully informed consent that this was an experimental procedure. RESULTS: The refractive results at 6 months after operation were within the range one would expect for PRK on corneas with a regular 'bow-tie' topography and similar level of myopia. No unusual problems were encountered. CONCLUSION: We feel that the corneal topography pattern of inferior steepening is not always a contraindication for PRK. The concept of a physiological 'displaced apex syndrome' is discussed and illustrated by corneal topography in different positions of gaze.

Adult↗
PubMed1996

Prediction of refractive outcome in penetrating keratoplasty for keratoconus.

We carried out a retrospective study to evaluate the relationship between vitreous cavity length, graft size, and final spherical equivalent refraction after penetrating keratoplasty (PK) for keratoconus. We found a straight-line relationship between vitreous cavity length and spherical equivalent for a one-surgeon series using the same technique throughout. The use of 0.25-mm undersized grafts shifted the results an average of 2.2 Dioptres in a more hypermetropic direction (p = 0.07 for the whole group, p < 0.01 for paired eyes). Hence the final spherical equivalent following PK for keratoconus can be predicted. Also, by altering the size of the donor graft button, the final refraction can be manipulated to some extent towards acceptable ametropia or to match the refraction of the fellow eye.

Adult↗