Diurnal variation of corneal sensitivity and thickness

PURPOSE: To measure the diurnal variation of central corneal sensitivity and thickness over 24 hours. METHODS: A noncontact pneumatic esthesiometer to measure central corneal sensitivity and an optical pachymeter to measure central corneal thickness were used on 20 noncontact lens wearers. These measurements were performed at 22:00 before 8 hours of sleep and on the following day on eye opening and at hourly intervals between 7:00 and 22:00. RESULTS: Central corneal sensitivity varied by 35% over the 24 hours. Sensitivity was significantly lower by 17.1 +/- 2.1% on eye opening and recovered to the level of the previous night after 4 hours. Corneal sensitivity continued to increase throughout the day but was not significantly higher. Central corneal thickness varied by 3.9% over the 24 hours. The mean overnight corneal swelling was 2.9 +/- 0.31%, and 2 hours after eye opening, the cornea had deswelled to the same thickness as the previous night. The cornea thinned further throughout the day, but there were no statistically significant differences between the values after 14:00. There was a high correlation between corneal sensitivity and thickness over time (r = 0.8; p < 0.05). DISCUSSION: Corneal sensitivity correlated with corneal thickness: both were higher on awakening and then decreased and remained below the levels measured the previous night. This may be due to physiological and/or environmental factors. The lack of significant differences between the values after 14:00 suggests that baseline may be measured at any time from 7 hours after eye opening.     

Corneal volume measures for monitoring contact lens induced corneal swelling: a pilot study

Background: This study investigated the use of corneal volume to monitor the corneal swelling response induced by wearing high plus power contact lenses. Methods: Twelve young non‐contact lens wearers were recruited with one eye fitted with a soft contact lens (Polymacon material, 38.6 per cent water, Dk of 9 and 0.27 mm centre thickness) and the fellow eye served as control. The treated eye was patched for two hours leaving the control eye uncovered. Central corneal thickness (CCT) was measured with non‐contact specular microscopy and corneal volumes (at three, five and 10 mm zones) were measured with a corneal topographer (Pentacam, Oculus Inc, Germany), before eye patching as well as immediately after and every 20 minutes for 100 minutes. Results: Subjects had similar CCT and corneal volumes between the two eyes before treatment. The treatment eyes showed a mean corneal swelling of 8.1 per cent immediately after lens removal. Corneal volume was significantly increased at the three (mean swelling of 5.9 per cent), five (5.6 per cent) and 10 millimetre (3.3 per cent) zones. It took 20 minutes for the corneal volume at the 10 mm zone to return to baseline but required 60 minutes for the three and five millimetre zones to return to the baseline level. The central corneal thickness was still significantly thicker 80 minutes after patching. Conclusion: Corneal volume could be a useful parameter to monitor corneal change when an event affects the entire cornea. Corneal volume combined with central corneal thickness could give more comprehensive information to monitor central corneal swelling.     

Corneal thickness changes following sleep and overnight contact lens wear in the primate (Macaca fascicularis)

Corneal thickness was monitored on seven cynomolgus monkeys (Macaca fascicularis) over a 76 hour period. During this time, corneal thickness measurements were also made on six monkeys after overnight wear of a hydrogel contact lens in one eye. Mean corneal thickness was 417 +/- 12 microns. An overall diurnal variation of 16 +/- 5 microns (3.8 +/- 1.2%) was found. During the first half hour after waking, corneal thickness changes ranged from -9 microns to +14 microns. After overnight contact lens wear, the cornea had swelled an average of 42 +/- 24 microns (9.1 +/- 4.8%). Following lens removal, the cornea returned to normal thickness within approximately 90 minutes. These results are similar to those found in humans and indicate that with respect to contact lens induced corneal thickness changes, the cynomolgus monkey is a suitable model for the physiological response to contact lens wear.     

Topographical corneal oedema

Corneal thickness changes were monitored across the cornea in 10 subjects during 7 days continuous wear of 3 types of hydrogel contact lenses of different back vertex powers. Analysis of topographical corneal thickness changes indicates that the periphery of the cornea swells significantly less than the central cornea. The effect is more dramatic with higher levels of central corneal oedema, and with lenses of higher minus power, in spite of their thicker lens periphery. An anoxic stimulus was also found to produce greater central than peripheral corneal swelling, indicating that tear exchange under the periphery of the contact lens is not a significant factor in limiting peripheral corneal swelling. It was concluded that the topographical swelling profile is not contact lens-related, but reflects a reduced swelling capability of the peripheral cornea, due to physical restraint in the limbal region.     

Incision depth affects the recovery of corneal sensitivity and neural regeneration in the cat

To assess the effect of incision depth on the recovery of corneal sensitivity and neural regeneration, adult domestic cats underwent either 8-mm circular nonpenetrating keratotomies or penetrating autografts. The contralateral eye served as control. Corneal sensitivity was determined at various intervals after surgery. The depth of incision in the nonpenetrating keratotomies, assessed by optical pachometry, ranged between 49 and 91% of total corneal thickness. The animals were ranked based on the depth of incision and the average sensitivity within the keratotomy over the 1-yr recovery period. A significant negative correlation was found between incision depth and the recovery of sensitivity (Spearman rank-order correlation r = -0.84, P less than 0.05). Some recovery of sensitivity was found in the center and periphery of the incised zone when incision depth was less than 53% of total corneal thickness. With deeper incisions, the center of the incised zone remained insensitive throughout the measurement period, while the periphery of the incised zone showed a slight recovery of corneal sensitivity, proportional to incision depth. The recovery of corneal sensitivity was higher in a small annular region just distal to the incision site. When incision depth exceeded approximately 53%, gold chloride impregnation showed that the resultant reinnervation was confined to single intraepithelial axons or localized regions of irregular epithelial fibers. With shallower incisions, the deeper stromal trunks were spared, resulting in the persistence of a reduced subepithelial plexus and basal epithelial leashes. We have shown that when an incision severs all stromal trunks, the neural regeneration is insufficient for functional recovery of corneal sensitivity at the center of an 8-mm keratotomy.(ABSTRACT TRUNCATED AT 250 WORDS)     

CORNEAL CHANGES FROM HYDROPHILIC CONTACT LENSES*

Corneal thickness and corneal curvature were measured before and after the wearing of hydrophilic contact lenses and it was consistently found that the thickness increased while the curvature virtually remained unaltered. On removal of the lenses the corneal returned to its normal thickness within two hours.     

Relation between optical coherence tomography and optical pachymetry measurements of corneal swelling induced by hypoxia

PURPOSE: To determine the relation between optical coherence tomography (OCT) and optical pachymetry (OP) measurements of corneal swelling induced by hypoxia. DESIGN: Experimental study. METHODS: One randomly selected eye of 20 noncontact lens wearers (10 males and 10 females, age 35.6 +/- 9.6 years) was patched during 3 hours of soft contact lens (SCL) wear while the contralateral eye acted as control. Central corneal thickness of both eyes was measured before and after SCL wear using OCT and OP in randomized order. RESULTS: Baseline central corneal thickness was 523.6 +/- 33.0 microm (mean +/- standard deviation [SD]) measured with OCT and 490.6 +/- 25.5 microm with OP. Immediately after contact lens removal, corneal thickness measured with OCT increased by 13.8 +/- 2.3% compared with 12.1 +/- 1.8% (paired t test: P <.001) measured with OP. Thereafter, corneal thickness decreased at the rate of 5.6% per hour for OCT and 5.4% per hour for OP. The difference in thickness between instruments before lens insertion, which was 33 microm compared with the difference after lens removal (edematous cornea), which ranged from 46 to 41 microm. The difference between instruments decreased during the corneal deswelling period after lens removal. The correlation coefficient between OCT and OP was 0.914 before lens insertion and 0.932 after lens removal. CONCLUSION: This study has demonstrated the difference of corneal thickness measured with OCT and OP. Although both instruments are correlated highly in all conditions tested, OCT may overestimate corneal thickness in normal and edematous corneas.     

正常戴角膜接触镜患者的角膜地形图变化

通过对戴角膜接触镜患者停镜后进行定期角膜地形图观察，发现戴角膜接触镜可引起角膜变形，如中心区不规则散光、缺乏正常角膜的由中心向周围逐渐变扁平和丧失辐射性对称。停镜后角膜恢复正常形态的时间为2～8周，平均为4．07±1．76周。最长时间为12周。停镜2周左右角膜变化较明显。提示屈光性角膜手术前，对戴角膜接触镜患者要定期检查角膜地形图，直至角膜形态恢复正常，才可进行手术治疗。     

Objective measurements of corneal light-backscatter during corneal swelling, by optical coherence tomography

PURPOSE: To demonstrate that corneal light-backscatter can be measured objectively during corneal swelling by optical coherence tomography (OCT). METHODS: One eye (randomly selected) of 20 non-contact-lens wearers (10 men and 10 women; mean age, 35.6 +/- 9.6 years) was patched during 3 hours of soft contact lens (SCL) wear. The contralateral eye acted as the control. Central corneal images were captured before and after SCL wear at 20-minute intervals over 100 minutes using optical coherence tomography (OCT) to obtain corneal thickness and light-backscatter profiles. OCT backscattered light of the epithelial layer (decided by the thickness measurements) and 10 equally divided layers of the remaining cornea were analyzed with a custom software program. Two baseline measurements were taken at different visits before lens wear to test the repeatability of light-backscatter measurements. RESULTS: From two baseline measurements, repeated measurements showed good repeatability of normalized backscatter results. Immediately after contact lens removal, total central corneal thickness increased significantly by 13.8% +/- 2.3% (mean +/- SD) compared with baseline (P = 0.0001, paired t-test) and then decreased during the deswelling course. Corneal backscattered light changed significantly (repeated-measures ANOVA [Re-ANOVA]: F((50, 950)) = 2.22, P = 0.0001) after lens wear, and a significant increase in backscatter was found in the epithelial layer (36.4%) and the most posterior corneal layer (35.6%) immediately after lens removal (post hoc test, P = 0.005). There was a strong correlation (r = 0.9375, P < 0.05) between the change in backscatter and corneal swelling during the deswelling period. The backscatter recovery rate was approximately the same for both epithelial and posterior layers after lens removal. CONCLUSIONS: Light-backscattering analysis with OCT seems to be a promising and repeatable method of objectively measuring corneal backscatter. This study has demonstrated that corneal backscattered light increased in the anterior and posterior layers of the cornea during corneal swelling induced by contact lens wear and eye closure.     

Pilot study on the influence of corneal biomechanical properties over the short term in response to corneal refractive therapy for myopia

PURPOSE: To study the short-term corneal response to corneal refractive therapy for myopia and correlate it with corneal biomechanical properties as measured with the ocular response analyzer. METHODS: Eight eyes from 8 young subjects were fitted with a reverse geometry contact lens, attempting a myopic correction of -4.00 D. Corneal resistance factor and corneal hysteresis (CH) were measured before contact lens fitting with the ocular response analyzer. These parameters were correlated with the degree of change in apical curvature, simulated keratometry, and central corneal thickness after 3 hours of contact lens wear (effect) and 3 hours after lens removal (recovery). RESULTS: There was a trend toward a faster effect and faster recovery of the orthokeratologic effect for corneas with less resistance in terms of biomechanical properties. Corneal resistance factor did not correlate significantly, however, with any of the topographic and pachymetric parameters. Conversely, CH was significantly correlated with changes in steep keratometry (0.758; P = 0.029) and central corneal thickness (0.755; P = 0.030) during lens wear and with changes in steep keratometry (-0.835; P = 0.010) during recovery. Overall, higher values of CH meant slower effect and recovery of the orthokeratologic effect. CONCLUSIONS: Short-term response of human cornea to corneal refractive therapy is correlated with the biomechanical properties of the cornea. Of the different theories supporting such involvement of corneal response to reverse geometry contact lenses, the most likely one seems to be the one assuming a faster response and faster recovery for corneas with lower resistance. Larger sample studies would be needed to clarify the involvement of corneal biomechanical properties on corneal response to orthokeratology.     

The measurement of corneal epithelial thickness in response to hypoxia using optical coherence tomography

PURPOSE: To determine if corneal epithelial thickness increases in association with corneal edema induced by wearing soft contact lenses during eye closure. DESIGN: Experimental study. METHODS: One eye (randomly selected) of twenty noncontact lens wearers (10 males and 10 females, age 35.6 +/- 9.6 years) was patched during 3 hours of soft contact lens (SCL) wear and the contralateral eye acted as a control. Corneal and epithelial thickness of both eyes was measured before and after SCL wear using optical coherence tomography (OCT). RESULTS: Immediately after contact lens removal, total corneal thickness was increased significantly by 13.8 +/- 2.3% (mean +/- SD) compared with baseline (P <.0001, paired t test) and after 100 minutes was still 4.5 +/- 2.3% thicker than baseline (P <.0001, paired t test). The control eyes showed no change in total corneal thickness (P >.05, paired t test). Immediately after contact lens removal, corneal epithelial thickness was increased by 1.7 +/- 4.8%, but this change was not statistically significant (P >.05, paired t test). Following contact lens removal, epithelial thickness changed significantly (Repeated measure analysis of variance [Re-ANOVA]: F((7,133)) = 4.91, p(H-F) < 0.001) over the next 100 minutes with thinning recorded at 60, 80, and 100 minutes (P <.05, paired t test). There was no significant change over time in epithelial thickness of the control eyes (Re-ANOVA: F(4, 76) = 0.91, p(H-F) = 0.464). CONCLUSION: OCT demonstrated that corneal epithelial thickness does not increase in response to hypoxia from SCL wear and eye closure, in contrast to a significant increase in total corneal thickness.     

Korneale Veränderungen nach dem Tragen von Orthokeratologie-Kontaktlinsen

BACKGROUND: Wearing orthokeratology contact lenses (OCL, Hecht-see free; Hecht, Germany) overnight can change corneal refraction by up to -4.5 dioptre (dpt) based on corneal adaptation to the double reverse surface of the OCL. This allows a temporary independence on glasses or contact lenses. It is known that the central corneal thickness decreases while the corneal thickness in the periphery probably increases. The aim of this study was to investigate the corneal changes of volunteers wearing OCL with in vivo confocal microscopy. MATERIALS AND METHODS: Five young adults (mean 22.8 years, three female, two male) with low to moderate myopia (range -1.75 to -3.5 dpt; sphere equivalent -2.7+/-0.59 dpt) were fitted with OCL of reverse-geometry design in both eyes. Lenses were worn in both eyes overnight and were removed immediately in the morning. The volunteers were examined with in vivo confocal microscopy using a combination of Heidelberg retina tomograph II and the Rostock cornea module before wearing the OCL and after the 1(st), 3(rd), 5(th), 7(th), 13(th), 20(th) and 25(th) nights. The central and mid-peripheral total corneal thickness as well as the epithelial thickness were examined in the morning between 7.30 am and 9.30 am. RESULTS: The central and the mid-peripheral epithelial corneal thickness was reduced significantly (p<0.05) from day 1 to the 13(th) day. This stabilized later until the the examination was concluded. No significant changes (p>0.05) were found in the central or mid-peripheral total corneal thickness after 25 days of wearing the OCL. CONCLUSION: Wearing OCL leads to a reduction in the central corneal epithelial thickness. Our inability to find an increase in mid-peripheral total and epithelial corneal thickness may be because the expected increase of the mid-peripheral cornea is limited to a defined area, which makes repeated measurements at a particular point difficult.     

Time to resolution of corneal edema after long-term contact lens wear

PURPOSE: To evaluate corneal thickness changes after soft contact lens (SCL) removal in laser in situ keratomileusis (LASIK) candidates. DESIGN: Observational case series. METHODS: A total of 100 eyes daily wearing SCL for at least six months were evaluated. The central corneal thickness (CCT) was measured by pachymetry immediately after lens removal and then repeated daily until it became stable. RESULTS: CCT immediately after lens removal was 557.4 +/- 32 microm, and when edema completely resolved was 521.8 +/- 25 microm. Corneal edema required two to 15 days after discontinuation of SCL wear to resolve. Corneal thickness stabilized in 74% of patients within the first week and in 26% of patients during the second week. Older patients and more primary corneal edema needed longer time to recover (P < .0001). CONCLUSION: Discontinuing SCL wear at least 15 days before keratorefractive surgery is recommended to achieve accurate pachymetry.     

Age-related modifications of corneal sensitivity

PURPOSE: To evaluate central and peripheral corneal sensitivity (CS) in relation to age. METHODS: Five hundred eyes of 320 healthy subjects (185 males and 135 females) were examined. The age of participants ranged from 20 to 90 years. All subjects were divided into 3 groups according to age. CS was assessed with the Cochet-Bonnet esthesiometer in the central cornea and in 8 peripheral points. The averages were used as the values of central and peripheral CS. RESULTS: In the young population, CS was equal in both examined zones (p > 0.05); although, with respect to the periphery after the fifth decade, it was significantly higher in the centre (p < 0.05). Both central and peripheral sensitivity decreased with age (p < 0.05), and such variations are represented by parabolic curves. No differences were observed between males and females. CONCLUSIONS: The age-related decrement of CS involves at first the corneal periphery and successively spreads toward the central zone. Topographical distribution and age-related modifications should be considered in clinical investigations of CS, especially in patients who underwent any corneal surgical procedure.     

Efficacy and safety of the soft-shell technique in cases with a hard lens nucleus

PURPOSE: To evaluate the efficacy and safety of the soft-shell technique in reducing corneal endothelial cell damage during cataract surgery in patients with a hard lens nucleus. SETTING: Miyata Eye Hospital, Miyakonojo, Miyazaki, Japan. METHODS: Sixty eyes of 57 cataract patients with a hard lens nucleus (Emery-Little classification grade 3 or higher) had phacoemulsification using the soft-shell technique with Healon((R)) (sodium hyaluronate 1%) and Viscoat (sodium hyaluronate 3.0%-chondroitin sulfate 4.0%) (soft-shell group) or with Healon alone (control group). The visual acuity, intraocular pressure (IOP), flare intensity in the anterior chamber, central corneal thickness, and corneal endothelial cell density were evaluated postoperatively. RESULTS: There were no significant IOP elevations in either group. The mean central corneal thickness in the control group was 539 microm +/- 26.0 (SD) preoperatively and 578 +/- 52.0 microm 1 day after surgery; the increase was significant (P =.0154). There was no significant change in the central corneal thickness in the soft-shell group. There were no statistically significant differences between the 2 groups in uncorrected visual acuity, best corrected visual acuity, IOP, flare intensity in the anterior chamber, and central corneal thickness throughout the follow-up. The rate of endothelial cell loss 3 months after surgery was 6.4% +/- 9.6% in the soft-shell group and 16.3% +/- 9.8% in the control group (P =.0003). CONCLUSION: The results suggest that the soft-shell technique is safe and effective in protecting corneal endothelial cells during cataract surgery in patients with a hard lens nucleus.     

Changes in central corneal thickness after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To evaluate changes in corneal thickness after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) in eyes with the same preoperative refraction, correlate these changes to postoperative refractive outcomes, and compare corneal healing process in a standardized subset of patients. METHODS: Central corneal thickness was measured by contact ultrasound pachymetry in 14 eyes of 8 patients with preoperative myopia of -6.00 D who had LASIK, and in 14 eyes of 8 patients with the same preoperative refractive error who had PRK. Measurements were taken preoperatively, and 1 week, 3, and 6 months after surgery. Data were evaluated and compared using the paired Student t-test and Pearson correlation coefficient. RESULTS: Mean preoperative central corneal thickness in the LASIK group was 549.14 +/- 37.4 microm, and in the PRK group, 552.64 +/- 34.9 microm. At 1-week postoperatively, mean central corneal thickness in the LASIK eyes was 467.28 +/- 29 microm and in the PRK eyes, 473.85 +/- 39.2 microm; at 6 months, central corneal thickness had increased in both groups compared to the 1-week values; LASIK eyes had a mean central corneal thickness of 481.42 +/- 23.0 microm and PRK, 481.50 +/- 35.3 microm. Mean postoperative refraction after 6 months was -0.48 +/- 0.30 D in the LASIK group and -0.67 +/- 0.35 D in the PRK group. CONCLUSION: Increase in central corneal thickness between 1 week and 6 months postoperatively occurred in both LASIK and PRK eyes, but differences were not statistically significant. No statistically significant differences were found in myopic regression between the two patient groups.     

Topographical thickness of the epithelium and total cornea after hydrogel and PMMA contact lens wear with eye closure

PURPOSE: To determine changes in topographical thickness of the epithelium and total cornea after hydrogel (2-hydroxyethyl methacrylate; HEMA or soft lens) and PMMA rigid contact lens wear with eyes closed, as measured by optical coherence tomography (OCT). METHODS: Epithelial and total corneal thickness in 18 neophyte eyes was measured with OCT at intervals of 10 degrees across a 10-mm zone of the horizontal meridian of the cornea, before and after 3 hours of soft and rigid contact lens wear with the eye closed. These measurements were repeated 20 minutes after removal of the lenses. RESULTS: Lens type, time, and location were found to be significant main influences (P < 0.0001) on corneal swelling in patched eyes, by three-way ANOVA, and there was a significant three-way interaction among lens type, time, and location (F((16,272)) = 1.78, P = 0.033). However, there was no significant main effect and interaction of epithelial thickness (F((16, 272)) = 0.33, P = 0.99). Immediately after removal of the lenses, total corneal thickness in the horizontal meridian was significantly greater with both soft and PMMA lenses (P < 0.001) at each location with each lens, compared with the baseline measurements. With both lenses, the increase in actual thickness and percentage of corneal swelling at the center was greater than at each peripheral point (excluding the first 10 degrees points; P < 0.005). HEMA lenses caused greater corneal swelling than the PMMA lenses at each location immediately after removal of the lenses (P < 0.005). CONCLUSIONS: This study shows that corneal swelling is dependent on lens type and corneal location when eyes are closed, but epithelial thickness across the horizontal corneal meridian does not change during lens wear with eyes closed. OCT is an efficient method of measuring topographical corneal and epithelial thickness in response to contact lens wear.     

Effects of phacoemulsification and extracapsular lens removal on corneal thickness and endothelial cell density in the dog

Twenty-one dogs were used to study the effects of phacoemulsification and extracapsular lens removal on corneal endothelium and corneal thickness. Specular microscopy revealed preoperative cell morphology and cell densities similar to man. After surgery endothelial cell counts significantly decreased 22% (central) and 13% (periphery) with phacoemulsification and 34% (central) and 31% (periphery) with extracapsular lens removal. Corneal thickness increased with both procedures. Endothelial cell pathology included cellular enlargement, increased pleomorphism, and focal cellular degeneration. Phacoemulsification time did not correlate with the degree of cell loss. Dog corneal endothelium responds to surgical trauma in a manner similar to man and maintains a functional monolayer via cellular enlargement and migration. The dog, therefore, represents a good animal model for the study of corneal endothelial disease in man.     

The effect of contact lens wear on the central and peripheral corneal endothelium

PURPOSE: To compare central and peripheral corneal endothelial cell morphometry in normal subjects and long-term contact lens wearers. METHODS: Endothelial cell density (ECD), coefficient of variation of cell area (CV), and percentage of six-sided cells were measured by contact specular microscopy in the corneal center and temporal periphery of both eyes of 43 long-term contact lens wearers and in 84 normal subjects who had never worn contact lenses. The latter group included 43 age- and sex-matched controls for the contact lens wearers. ECDs were corrected for magnification changes due to corneal thickness. RESULTS: Central ECD (2,723+/-366 cells/mm2, mean +/- SD) was significantly higher than peripheral ECD (2,646+/-394 cells/mm2) for the normal group (p = 0.01) but not for the contact lens wear group (2,855+/-428 cells/mm2 central, 2,844+/-494 cells/mm2 peripheral, p = 0.84). Peripheral CV was significantly higher than central for normal subjects and contact lens wearers and was significantly higher in both center and periphery in contact lens wearers than in controls. Central percentage of six-sided cells was significantly higher than peripheral for normal subjects and contact lens wearers and was lower in both center and periphery in contact lens wearers than in controls. CONCLUSIONS: Central ECD was significantly higher by 3% than peripheral ECD in normal subjects, but not in contact lens wearers. The results suggest that contact lens wear causes a mild redistribution of endothelial cells from the central to the peripheral cornea. A reversal of this redistribution after contact lens wear is discontinued for refractive surgery could mask mild central endothelial damage from the refractive procedure.     

Photokeratoscopy in fitting contact lens after penetrating keratoplasty.

The formula based on keratometric readings which is generally used is unsatisfactory for fitting contact lenses after penetrating keratoplasty, possibly owing to lack of information on the peripheral corneal toricity. In these studies a photokeratoscope was used to examine the entire graft topography. In all cases the corneal configuration became more normal after suture removal, but a considerable toricity still remained, especially near the graft-host junction. One month after removal of sutures spherical hard contact lenses (polymethylmethacrylate, PMMA) were fitted to 30 patients in accordance with data obtained by computerised analysis of the photokeratograms. Of the 30 patients (contact lens wearers) 27 (90%) obtained a stable vision of better than 20/30 for eight hours daily, and 24 (80%) achieved a stable vision of 20/20 for their full waking hours. After one year the contact lens wearers showed a significant decrease in the extent of astigmatism when compared with the non-contact-lens wearers (10 patients). These results suggest that the photokeratoscope can be more useful than ordinary keratometers in fitting contact lenses after keratoplasty, and that hard contact lenses have moulding effects on the graft topography.