Corneal sensitivity recovery after photorefractive keratectomy (PRK)

Ophthal. Physiol. Opt. Vol. 16, No. 3, pp. 250-256, 1996 The College of Optometrists. Published by Elsevier Science Ltd Printed in Great Britain 0275-5408/96 $15.00 + 0.00

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S0275-5408(96) 00002-6

Abstracts Papers presented at the British Congress of Optometry and Vision Science, Bradford University, UK on 5 - 6 September 1995 Sponsor: Carl Zeiss Ltd

PAPER S E S S I O N

I--CLINICAL

OPTOMETRY

the Oxford Modular Cataract Image Analysis System. After the scleral lenses were worn. forward light scatter values increased significantly at all the three angles (3.5°: Fi.t7 = 65.69, P < 0.001; 10°: El.17 = 37.30, P < 0.001; 28°: Fur 7 = 26.66, P < 0.001). Backward light scatter also increased significantly with the presence of corneal oedema (Fl.17 = 4.80, P < 0.001). A significant correlation was found between the differences on forward light scatter recorded at the different angles. However, no significant correlation was found between the increase in forward and backward scatter recorded by the two techniques. We conclude that both forward and backward light scatter can be good indicators of corneal transparency.

Moderator--Professor Alan Tomlinson Morphometric analysis of the corneal endothelium

A. J. Jackson and D. B. Archer Department

of Ophthalmology,

Queen's University, Royal

Victoria Hospital, Belfast, Northern

Ireland

Early developments in specular microscopy and quantitative corneal endothelial image analysis have resulted in the publication of material describing the morphometric appearance of the mosaic in health and disease. A broad range of morphometric parameters, including cell area, diameter, perimeter, form and shape, have been used to describe cellular appearances. In may cases the selection of parameters appears inappropriate and uncoordinated. In this study, the corneal endothelium of 300 normal, traumatised and pathological corneas was photographed using the Keeler Konan Pocklington specular microscope. The morphometric characteristics of endothelial cells were assessed using the Kontron Mop II semiautomated image analysis system. Results indicate that cell density and mean cell area measurements provide the most useful indices of agerelated, post-traumatic and pathological cell loss. Cell perimeter and cell diameter measurements add value in those cases where cellular migration occurs in response to trauma or localised cell loss. The quantification of intercellular cell area variability (polymegethism), and cell shape variability (pleomorphism), provides additional data on the effects of physiological stress. Cell form factors, which exhibit large intercellular variability, prove unhelpful when applied to global populations of cells. The authors conclude that in performing quantitative analysis of the corneal endothelium, specular microscopists should apply informed restraint when selecting parameters for morphometric analysis. The relative merits of a range of morphometric parameters are discussed.

Corneal sensitivity keratectomy (PRK)

~Department University,

of

of

Vision

Glasgow

Sciences,

G4 0BA;

perimental Ophthalmology,

photorefractive

Glasgow

Caledonian

and 2Department

St T h o m a s '

of Ex-

Hospital, London,

UK

Purpose: To establish the pattern of recovery of corneal sensitivity postPRK using a non-invasive aesthesiometer.

Methods: Two studies were undertaken. (1) A longitudinal study monitoring the recovery of corneal sensitivity in 10 patients over one year, following a PRK correction of - 6 D / 6 m m (correction (D)/ablation diameter (mm)). (2) A transverse study examining corneal sensitivity one year postoperative on 68 patients who underwent various correction procedures: - 3 D/5 mm (n = 16), - 3 D/6 mm (n = 13), - 6 D/5 mm (n = 14), - 6 D / 6 m m (n = 12) and -6D/Multizone (n = 13).

Results: (1) Corneal sensitivity showed an immediate drop at week 1

Teresa Matilla, William Douthwaite and Mark Hurst University

after

Paul J. Murphy ~, Melanie C. Corbett 2, David P. S. O'Brart 2, Seema Verma 2, Sudi PateP and John Marshall 2

Forward and backward light scatter measurements in the assessment of corneal oedema Department of Optometry, Bradford BD7 IDP, UK

recovery

(P < 0.05). with a further decline at week 2 (P < 0.05). Sensitivity recovered slowly over the following months. (2) Corneal sensitivity was reduced in the PRK-treated eyes when compared to normal noncontact lens wearing eyes (P < 0.01). No specific procedure effect was found.

Bradford,

As the cornea swells it loses its transparency, thereby increasing both forward and backward light scatter. The purpose of this study was to investigate the changes in corneal transparency by means of scatter assessment. Both forward and backward light scatter measurements were obtained from 18 normal corneas, before and after the induction of corneal oedema with sealed scleral lenses. Forward light scatter was measured at 3.5, 10 and 28 degrees, using a portable straylight meter as developed by van den Berg. Backward light scatter measurements were obtained by computerised linear scanning densitometry of Scheimpflug images using

Conclusions 1. The pattern of sensitivity change occurring is: (a) an initial rapid drop, followed by: (b) a slow recovery over 1 years. 2. At one year, sensitivity is still below both normal and contact lens wear levels. 3. The extent of sensitivity loss is not influenced by the depth of ablation.

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